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In several crop species, the harvested part of the crop (primary product) must be processed to extract the economically useful part (final product). The standard evaluation of new technology in these crops is normally based on the quantity of final product per unit land area (final production), which is the product of primary production and the proportion of final product that is extracted from the primary product (extracted product). This may be valid in terms of biological productivity, but in terms of commercial viability it is not satisfactory. Costs of harvest transport and initial processing of the primary product are normally more closely related to total primary production than to final production. Identical values for final production may be obtained through high primary production combined with low extracted product or vice versa. In the latter case, where primary production is less, the costs of harvest, transport and initial processing per unit final product will be less. The standard evaluation, which gives equal weightage to primary production and extracted product, does not detect these differences in costs. A simple model is developed for sugar production from cane to make valid comparisons between the profitability of different treatments. The model can readily be adapted for other crops such as sugar beet, oil palm and cassava.

Thirteen cultivars of elephant grass (Pennisetum purpureum) were grown in the wet tropics over a period of 30 months for evaluation as a source of paper pulp. The first five ratoon harvests were at 3-month intervals, and the following two ratoon harvests at 6-month intervals. Mean annual yields were similar under both harvest regimes. At 3-month harvest intervals four cultivars were consistently high yielding and averaged 69.5 t ha−1 of total dry matter and 47.1 t ha−1 of stem dry matter, but at 6-month intervals yield rankings were less consistent due to variable lodging. Limited pulping studies suggested that cultivars did not differ greatly in pulping characteristics. Crude protein content ofleaves averaged 15% and quality was generally adequate for direct feeding to cattle. In crops harvested at intervals of 3 months mean temperature was the environmental variablwe mostclosely associated with total dry matter yield.

International audience; The nitrogen economy of the crop is a critical driver of biomass and grain production, and its importance is reflected in a large, worldwide research effort to link nitrogen, growth and yield. Particular research questions require measurement of specific traits, hence the need to quantify multiple, often complementary traits including crop nitrogen uptake, nitrogen use efficiency and its components, nitrogen concentration in the crop and its parts, down to relevant enzymes (e.g. nitrate reductase) and other products of gene expression. Nitrogen uptake, however, is co-regulated by both soil nitrogen availability and crop biomass accumulation; hence, crop nitrogen uptake or shoot nitrogen concentration reflect univocally crop nitrogen status only if comparisons are made at similar biomass. Although the allometric relationships between biomass and nitrogen uptake have been established for over two decades, many studies still report results in terms of nominal treatments, e.g. high vs low nitrogen, which are uninformative; curves relating yield and fertiliser rate, which are of local interest but provide little insight on the underlying processes and have low generic value; and nitrogen-related traits that are incomplete or inadequate to quantify crop nutrition status. Often, the allometric relationships between nitrogen and biomass are overlooked. In this opinion paper, we summarise the already well established concepts of dilution curves and nitrogen nutrition index, outline the standard partitioning of nitrogen use efficiency, and highlight the confounded effects in nitrogen use efficiency when the allometric relationship between nitrogen uptake and biomass is ignored. A sample of recent papers is used to survey the most common approaches to characterise nitrogen related traits. We illustrate the application of dilution curves and nitrogen nutrition index in the assessment and interpretation of crop responses to agronomic practices and comparisons of wheat cultivars and maize hybrids.

a b s t r a c t Maize provides an important source of forage for the maize-dairy farmers in Kenya. However, due to small farm size, maize cannot supply all the feed needed for dairy cattle and forage is in short supply in the dry seasons. This paper examines practices to increase the health and use of maize and increase forage quality and quantity. The paper uses data from participatory on-farm research on cultural management practices of maize and on-station field trials in which plants were artificially infected with maize streak virus disease (MSVD) in the intensive maize-dairy production systems in central Kenya. Findings showed that smallholder farmers have deliberately changed the maize management practices by planting densely and systematically thinning the crop to obtain both fodder and grain. They perceived MSVD to have the greatest effect on forage yields and to be a difficult disease to control. Maize management trials showed that increasing plant density increased forage yields by up to 41% but decreased grain yields by up to 17% when specific thinning regimes were applied fairly late in the growth of the crop. However, grain yields were maintained when maize was planted at high density and then progressively thinned for forage during the growing season according to the crop situation or need for forage. The on-station research is the first study on the impacts of MSVD on maize forage and was carried out to increase production of forage during the wet seasons through use of resistant cultivars and agronomic interventions with a view to mitigating forage shortages during the dry seasons. MSVD infection was achieved with artificially infected leafhoppers (Cicadulina mbila (Naude) (Hem.: Cicadellidae). In the 2001 short rainy season (SRS), early infection (14 days after crop emergence) reduced thinning yields by 43% in the susceptible cultivar, H511, compared to only 22% in a tolerant one, KH 521. Stover yields were reduced by 24% in H511 while there were no significant losses in KH 521. Interestingly, the local landrace, Gikuyu, was tolerant of MSVD in terms of grain yield but not thinnings. Forage from crops infected 35 and 56 days after crop emergence did not differ significantly from the uninfected controls. In the 2002 long and short rainy seasons, early infection with MSV again reduced thinning and stover yields whereas fertilizer and plant density did not significantly affect the influence of MSVD on either maize forage or grain yields. Use of tolerant cultivars provided insurance against forage and grain yield losses caused by early infection by MSV, but yield benefits varied with season. With respect to forage quality, MSVD had a beneficial effect on susceptible cultivars (H511 and H614) due to the higher crude protein (CP) and lower neutral detergent fibre (NDF) concentrations of infected material in the early stages of growth. However, the reduced yields due to MSVD negate any advantage of increase in CP in infected material of susceptible maize cultivars. Further, the benefit of breeding for high NDF concentrations as a defense mechanism against disease effects is disadvantageous to improving quality of maize forage.

Several papers reported that the incorporation of Bt genes into rice caused morphological and physiological changes. In this paper, we try to reveal whether the incorporation of a Bt gene ( cry1C * or cry2A *) into Minghui63 (MH63) and Shanyou63 (SY63) will affect the yield performance, and its agronomic and physiological mechanism underlying the yield differences. Field experiments were conducted in 2009 and 2010 at Zhangbang village, Wuxue city (29°51′N 115°33′E) and Dongshantou village, Xiaonan county (30°56′N 113°54′E), Hubei Province, China from May to October. Treatments were arranged in a randomized complete block design with three replications, and each replication contained three genotypes in 2009 and six genotypes in 2010. No significant differences in grain yield, biomass, leaf area index (LAI), nitrogen accumulation and growth-promoting phytohormones content were observed between MH63 ( cry2A *) and MH63, except that MH63 ( cry2A *) had significantly lower grain yield than MH63 at Wuxue city in 2009. MH63 (cry 1C *) had lower grain yield than MH63 and MH63 ( cry2A *) at all site-years, and the yield reduction was mainly ascribed to the reduced grain filling percentage. Growth analysis revealed there were no differences in biomass production and nitrogen accumulation between MH63 ( cry1C *) and MH63. The incorporation of cry1C * brought a significant reduction in the content of growth-promoting phytohormones in the superior spikelets, which highly correlated with grain filling percentage of MH63, MH63 ( cry1C *) and MH63 ( cry2A *). There were no significant differences on grain yield and growth performance among all the three hybrids by crossbreeding MH63, MH63 ( cry1C *) and MH63 ( cry2A *) with Zhenshan 97A. More endeavors are encouraged to examine the physiological and genetic mechanisms behind the variations.

Even though planting cotton early in the season is advantageous, the cold sensitivity of cotton seedlings and low germination rates, especially in the areas experiencing low temperatures, are the main obstacle for the early seasonal planting. A total of 106 genotypes from three different species; Gossypium hirsutum L., G. barbadense L., and G. herbaceum L. were screened for cold tolerance using three different approaches. Furthermore, the best screening method to differentiate between the genotypes for cold tolerance, and to predict their field emergence rates was also determined. In detail, optimal germination percentages were measured at 30 °C with the results ranging from 61% to 99%. On the other hand, cold temperature germination rates and emergence percentages ranged from 8% to 82% in paper test and from 8% to 88% (the 7th day after planting) in sand test at 18 °C, and field emergence percentages ranged from 44% to 77% at 28 days after planting. A significant difference between cotton species in terms of their tolerance to cold was observed. That is, G. barbadense genotypes had higher germination rates than the other two species in the three methods used. There was no correlation between optimal germination rates and field emergence percentages. Among cold temperature germination methods, the 18 °C paper test was better in predicting of field emergence percentage, in differentiating between genotypes in terms of their cold tolerance and in determining seed vigor. G. hirsutum cultivars; 8106-2, AYDIN-110, CORINA, DP-388, DPL-50, DPL-5614, NAZILLI-342 and one G. barbadense cultivar, GIZA 70 were more cold tolerant among all the cotton cultivars screened in this study.

The paper investigates management and cultivar type effects on pearl millet stover yield and fodder quality. Sixteen pearl millet cultivars available to farmers in India were selected to represent three cultivar types: (1) traditional landrace germplasm from the arid/semi-arid millet production zones, (2) improved dual-purpose (grain and stover) open-pollinated varieties incorporating differing amounts of traditional landrace germplasm and (3) commercial, grain-type F1 hybrids, bred for use in the arid/semi-arid zone. The cultivars were grown for 2 years (2000 and 2001) at high fertility (HF: 65 kg N ha −1 and 18 kg P ha −1 ) and low fertility (LF: 21 kg N ha −1 and 9 kg P ha −1 ). Within each fertility level high (HP) and low (LP) plant population densities were established by varying sowing rate and then thinning to the target populations (HP: 11 plants m −2 and LP: 5 plants m −2 ). Stover fodder quality traits (nitrogen concentration, sugar content, in vitro digestibility and metabolizable energy content) were analyzed using a combination of conventional laboratory analysis and near infrared spectroscopy. In general, fertility level and cultivar type had strong effects on grain and stover yields, and on a range of stover nutritional quality traits, but with significant year interactions. In contrast, the effect of population density on these variables was largely insignificant. Higher fertilizer application significantly increased grain and stover yields and stover nitrogen concentration, in vitro digestibility and metabolizable energy content. As a result, fertilization resulted in significant increases in the yields of both digestible and metabolizable stover. Landrace cultivars as a group produced higher quality fodder than modern hybrids, but at a significant cost in grain yield. Dual-purpose, open-pollinated cultivars were generally intermediate between the landraces and hybrids, in terms of both stover quality and grain yield, but produced the highest yields of both digestible and metabolizable stover. The paper discusses the implications of these findings for Indian pearl millet farmers with various resource levels and farming objectives.

Whereas the concept that availability of resources drives seed production is sound in principle, it is incomplete as there are many solutions to the allocation of resources that derive from the trade-off between number and size. This paper examines evolutionary aspects of this trade-off in annual grain crops. The analysis is centred on the working hypotheses that, for a given species and environment, allocation of resources to reproduction involves (H1) high plasticity in seed number, which allows for variable resource availability, and (H2) a relatively narrow range of seed size that results from evolutionary and agronomic selection. Comparisons between crops and fish are used to highlight common evolutionary elements in taxa where parents provide little or no care to their offspring, with the consequence that both number and early survival of offspring, hence fitness of parents, are partially related to embryo size and reserves. The plasticity of seed number in relation to availability of resources is analysed against the established relationship between offspring number and parent growth rate during critical stages. The notion that seed size is under stabilising selection is analysed against three conditions: (1) mean seed size is conservative for a given species and environment, (2) seed size affects fitness, and (3) seed size is heritable. Databases from published papers were compiled to analyse the relative variability of seed size and number, and the heritability of seed size. Evidence for and against the link between seed size and parental fitness is revised using the Smith–Fretwell model as framework (Am. Nat., 108, 499–506). The proposal of high plasticity of seed number and narrow variability of seed size resulting from stabilising natural selection is generally consistent with evolutionary and genetic considerations. Agronomic selection may have reinforced natural selection leading to relatively narrow seed size in species such as wheat and soybean, where cultivated types retained high plasticity for seed number. In contrast, selection for one or few inflorescences in crops like sunflower and maize may have morphologically reduced seed number plasticity and increased variability of seed size and its responsiveness to resource availability in relation to their wild ancestors.

Cotton (Gossypium hirsutum L.) cultivars containing the cryIAc gene accounted for 81% of South Africa's cotton production in 2004. Current research on Bt cotton in developed countries has revealed that this transgenic crop provides a key means for enhancing yields and boosting profits. Our study was designed to assess the agronomic efficiency of Bt cotton particularly in South African commercial (Paper 1) and small-scale (Paper 2) farming systems. Over several consecutive years, we compared yield boll distribution patterns (using a plant mapping analysis) of a Bt cultivar (NuOpal) with a conventional nearly isogenic line (DeltaOpal). Compared with the non-Bt cultivar, Bt cotton had better early boll retention rates at the first and second positions on the fruiting branches. Beyond the third position this trend was reversed, indicating that non-Bt cotton varieties offset losses occurring at the first two positions by producing fruits at further positions. Bt cotton thus had a higher average boll weight, shorter vegetative cycle, earlier boll opening, and 13% higher yield potential on average than the conventional control. These results indicate that using the transgenic variety provided better protection against bollworm as compared to chemical treatments—which are likely not effective at the onset of bollworm infestation and do not protect the first bolls. These observations demonstrate the advantage of transgenic Bt cotton when grown under near optimal conditions.

Global change poses major challenges for research in fields ranging from crop improvement to water and fertilizer management. Plant genomics is often promoted as a likely source of breakthroughs in understanding plant response to temperature and water stress. This special issue includes papers that range from consideration of gene-to-phenotype associations to papers at the system scale that examine successes and problems with linking physiology and genomics for global change research. Key themes covered include “How genomics can contribute to global change research,” “Genomics and basic understanding of crop responses to the environment,” and “What can field-level physiology bring to genomic research?”. Extrapolation from the model species arabidopsis [Arabidopsis thaliana (L.) Heynh.] has proven more problematic than anticipated, but new techniques and advances in gene sequencing of crop species helps compensate for such difficulties. Physiological research complements genomics by bringing an understanding of the response of the whole plant or crop to differing environments. Physiology also leads to an appreciation of how macro-scale processes such as photosynthesis and partitioning add biological meaning to genotype-by-environment interactions that are significant statistically but otherwise are not meaningful. Furthermore, physiologists have traditionally measured phenotypes in careful detail, and they have a clear role in adding precision to research on gene-to-phenotype associations. Research on crop response to global change has much to gain from strengthened collaboration between genomics and field-level crop physiology.

Tillering is an important adaptive feature of pearl millet (Pennisetum americanum [Pennisetum glaucum]) to the unpredictable growing conditions of dry areas of the semiarid tropics. Yet, this feature has largely been ignored in the development of simulation models for pearl millet. The objective of this paper is to parameterize and validate a leaf area module for pearl millet, which dynamically simulates crop leaf area from the leaf area of individual axes through simulating inter-axis competition for light. To derive parameters for the model, four cultivars (BJ 104, WRajPop, HHB 67 and RCB-IC 911), contrasting in phenology and tillering habit, were grown under well-watered and well-fertilized conditions across a range of plant densities in three experiments at two locations in India (Patancheru, Andhra Pradesh and Jodhpur, Rajasthan) during 1996 and 1997. For selected plants, observations on the number of primary basal tillers and on the number of visible, fully expanded, and senesced leaves on each axis were made twice a week throughout the growing season. Occurrence of panicle initiation (PI) was observed in two experiments only, but data were complemented by published and unpublished data, obtained for comparable cultivars. Parameters were obtained for the time from emergence to PI as a function of daylength, leaf initiation rate, ate of leaf and tiller appearance, and the leaf senescence rate. Parameters for leaf size were determined in a previous paper. Our parameter estimates compared well with published data and were, with the exception of time to PI and leaf size, mostly independent of cultivar, axis and density. Genotypic effects on productive tiller number could be attributed to differences in main shoot leaf size. Validation of the leaf are module showed that the module adequately reproduced the effects of density, photoperiod and genotype on the leaf area of individual axes and on productive tiller number. This was despite the fact that the reduction in leaf area of non-productive tillers was achieved in the module through a reduction in leaf size, whereas the crop reduced leaf area through a reduction in leaf number. Our results indicate that leaf area index (LAI) of a tillering crop can be simulated adequately by simulating LAI from individual leaf area and incorporating the effects of competition for light

Pearl millet (Pennisteum americanum L.) is an essential crop in farming systems of the dry areas of the semi-arid tropics and its tillering habit is an important adaptive feature. This is the first paper in a series aiming at developing and validating a pearl millet simulation model that recognises tillers as functional entities, analogous to intercrops. The objective of this paper is to quantify the effects of total leaf number per axis (TLN), cultivar, plant density and axis number on parameters that are used to simulate potential leaf area per plant. Four cultivars with different phenology and tillering habit were grown under well-watered and well-fertilised conditions at two locations in India, covering a range of daylengths and plant densities. For selected plants, the area of fully expanded leaves was measured non-destructively. A bell-shaped function adequately described the relationship between individual leaf area and leaf position on an axis. Its shape was determined by the position (X0) and area (Y0) of the largest leaf and by the breadth and skewness of the leaf area profile curve. TLN affected all four parameters, although the association with Y0 was weak. Cultivar only affected Y0, suggesting that parameterising new cultivars is straightforward. The observed density effect confirmed that competition for light between axes started during stem elongation. The results highlighted the consistent differences between leaf area profiles of main shoots and tillers. For a high-tillering crop like pearl millet, modelling leaf area dynamics through individual leaves is justified, as this approach can potentially deal with cultivar and environmental effects on tillering.

This paper discusses the modifications needed to be made to the biometrical breeding method proposed for single crosses in a previous paper ( Lawrence and Senadhira, 1998 ) when used with pedigrees founded on three-way and double crosses. It is suggested that, if the S0 and S2 generations of the latter replace the F1 and F3 generations of the pedigrees of single crosses, it is possible for breeders to evaluate three- and four-parent crosses in the same programme as single crosses.

This paper reviews the origins and general botany of Phaseolus vulgaris , the different cropping systems used for bean production, the agronomic and biological factors which most limit crop yield, and the strategies for improvement in this crop. While the common bean originated in the Americas, it is now grown widely in both the old- and the new world and in Africa, with the most suitable ideotype, and the disease and insect resistance factors needed for a particular production area, dependent on local conditions. Marked color and seed-type preferences further complicate the breeding and adoption of new varieties. The paper considers both conventional approaches and marker-assisted methods for breeding in this crop. The common bean is a crop with multiple disease and insect pests, and the ability to quickly and effectively select plants carrying multiple or different types of resistance gene is essential to an orderly and efficient processing of progeny.

The study reports achene germination under varying laboratory conditions, transplantability, survival of seedlings in saline soils, and a field cultivation trial of Grindelia camporum (gumweed) in a semi-arid and hot climate. Achenes placed under a thin layer of soil, on wet filter paper, or in water, at ambient temperature and a diffuse daylight/night cycle germinated at 75%, 69% and 65% respectively. In total dark at ambient temperature compared with 8°C, the achene germination in water was 41% and 48%, respectively. During the 2-step procedure of a cool pretreatment at 8°C in the dark for 4 days followed by a shift to ambient temperature and diffuse daylight/night cycle, however, germination rose to 74%. Achenes germinated in water or on wet filter paper survived well when transplanted to soil whereas those germinated under a thin layer of soil, when uprooted, did not withstand transplantation. Survival of seedlings in saline soils having electrical conductivity of 4, 8, 12 and 16 mmho/cm was, respectively, 31%, 18%, 7% and zero as compared with 91% in the normal soil (3 mmho/cm). During the growing season of 363 days, two crops were harvested yielding 1.36 kg m −2 year −1 biomass and 128 g m −2 year −1 crude resin.

Rainfed crop production in the subtropics is a risky enterprise due to high rainfall variability. When planting opportunities occur, farmers face risky choices because the consequences of decisions made at planting are uncertain. This paper presents a general approach to generating the information required to assistt in making planting decisions in climatically variable subtropical environments. The approach involved coupling a sorghum growth simulation model to long-term sequences of climatic data to provide probabilistic estimates of yield for the range of decision options, such as planting time and cultivar maturity, for a range of soil conditions. The likely change in the amount of stored soil water with delay in planting was also simulated to account for the decision option of waiting for a subsequent planting opportunity. The approach was applied to three locations (Emerald, Dalby and Roma) in subtropical Australia. Production risk varied with location, time of planning, soil water storage, and cultivar phenology. Yield responses to these factors were associated closely with differences in leaf area development and degree of depletion of the water resource. The probabilistic estimates of yield and change in stored soil water provided in this paper can assist decision-makers with risky choices at planting in subtropical environments. Such information can be used in decision analysis or in computerized decision support, where decision-makers, and their risk preferences, can interact directly with the information.

The papers in this special issue are mainly about intercropping research with the aim of increasing our understanding of processes determining yields of component crops and overall intercrop productivity. It is necessary to conduct adaptive research which would benefit farmers directly by providing management options available to them in a particular location. This paper outlines a procedure for conducting such adaptive research in intercropping. Seven steps are identified. They are: 1. 1. Problem identification and/or clarification of expected agronomic and economic impact at farmer level. 2. 2. Determination of crop responses to the several major limiting factors. 3. 3. Choice of crops. 4. 4. Determination of competitiveness between component crops under a standard cultural practice. 5. 5. Adjustment of competitiveness of component crops by agronomic methods. 6. 6. Choice of cultivars. 7. 7. Evaluation of a new intercropping system, or new components, in the farmers' fields.

This is the third paper in a series that examines the genotypic and environmental controls of leaf area dynamics in grain sorghum. In this paper, genotypic variation in leaf area senscence was firstly quantified both at the whole plant level and at the level of individual leaves. Green leaf area was then simulated at both levels, and predictions were compared with independent data on crop leaf area index. At the whole plant level, senesced plant leaf area (SPLA) was modelled as a logistic function of thermal time after emergence, where the asymptote of the relationship is determined by maximum leaf area produced per plant. At the level of individual leaves, where leaf size was predicted, SPLA was simulated by a constant rate of senescence of individual leaves. The relationship at the two levels of simulation were both affected by different leaf numbers per plant. While there were genotypic differences in the senescence of sorghum leaf area, the genotypic control of sorghum leaf area dynamics was generally less influential than the effect of the environment. Relationships to predict SPLA were added to those to predict total plant leaf area (TPLA), previously developed in this series, to enable prediction of green leaf area development of sorghum crops. There was little difference in the accuracy with which the models at the whole plant and individual leaf levels simulated independent data. The model at the whole plant level was simpler and required less initial information. The model at the level of individual leaves was more complex and needed greater information, but provided a more detailed treatment of leaf area dynamics. The choice between the two approaches will depend to a large degree on the demands of the study for which a sorghum leaf area model is to be applied.

Leaf area dynamics are controlled by genotypic and environmental influences. In this series of papers, general models of leaf area dynamics of uniculm and tillering sorghum ( Sorghum bicolor (L.) Moench) at the whole plant and individual leaf levels were developed to examine and quantify both genotypic and environmental controls. Green leaf area was modelled by examining leaf area production and senescence separately. Data from field experiments involving broad ranges of hybrids and environments were collated and analysed. Crops were grown with adequate water and nutrient supply. In this paper, a general framework to model leaf area production at the whole plant level is presented. Accumulation of total plant leaf area (TPLA) (without losses due to senescence) was simulated using a logistic function of thermal time (TT) from emergence and it increased to its maximum value (TPLA max ) shortly before flowering. To calculate TT, base optimum and maximum temperatures of 11, 30 and 42° C respectively were derived by examining the effect of temperature on rate of appearance of fully expanded leaves. Hence, TT incorporated the major effect exerted on TPLA by temperature. Most remaining genotypic and environmental variation in TPLA was related to variation in TPLA max . Values of TPLA max were predicted from total leaf number on the main culm (TLN) and fertile tiller number per plant (FTN) by allowing for a curvilinear increase in TPLA max with TLN and a sequential decrease in total leaf area produced by successive surviving tillers relative to that on the main culm. The potential genotypic and environmental controls on TPLA, introduced via factors affecting TLN and FTN, were considered. Frr seven hybrids grown in eight environments (locations and times of planting), this simple general model accounted for 93% of observed variation in TPLA with time, with a root mean square deviation of 664 cm 2 for observed values of TPLA ranging from 161 to 11 302 cm 2 .

Routines controlling development of leaf area in the CERES-Maize model have been misinterpreted in recent papers, owing to an inaccuracy in parameter definition in the published documentation of the model. This paper provides the correct description of functions for leaf-area development in CERES-Maize, and tests the performance of these functions. Given the correct definitions of the variables cumph , as the cumulative number of visible leaf tips, and xn as the next leaf which will emerge on the plant, CERES-Maize simulates leaf-area expansion per plant as a function of the number of emerged leaf tips. A test of the leaf-canopy routines in CERES-Maize indicated that constants, used in the functions describing both rate of appearance of leaf tips and rate of leaf-area expansion per plant, needed calibration for predicting leaf-area development of the tropically adapted hybrid maize Dekalb XL82.

Birch, C.J., Carberry, P.S., Muchow, R.C., McCown, R.L. and Hargreaves, J.N.G., 1990. Development and evaluation of a sorghum model based on CERES-Maize in a semi-arid tropical environment. Field Crops Res., 24: 87-104. This paper reports on the development and evaluation of a grain sorghum model (CERESSorghum ( SAT ) ) for use in the semi-arid tropics. The model was developed from a version of CERESMaize, previously adapted for use in this climatic zone. Functions for phenology, leaf growth, leaf senescence, assimilate accumulation and grain growth were modified using a small subset of sorghum data and validated against a much larger field-data set. When tested with cultivar De Kalb DK55 at Katherine, Northern Territory, the model successfully predicted grain-yield with a root mean square deviation of 0.972 to ha- ~ over a range of sowing dates and water regimes resulting in observed yields ranging from 1.56 to 6.28 t ha -~. Deviations of predicted from observed yields were no greater than those of maize predictions by the parent model. Prediction of components of yield and biomass were also satisfactory. Calibration required 28 changes to the CERES-Maize(SAT) model, of which 15 were changes to coefficients in equations rather than substantial changes to the model. Because of the ease of conversion and the time-use efficiency found in these analyses, the techniques used in this paper could have application where locally calibrated models are required.

The paper compares food and straw fodder traits in wheat lines of 6 different CIMMYT wheat trials tested across 32 environments of South Asia (India, Nepal, Bangladesh and Pakistan). Experiments were conducted in the main spring wheat season with sowing time of mid-November to mid-December and harvest between March to April. Investigated and compared were grain yield (GY), straw yield (SY), straw nitrogen (N) content, neutral (NDF) and acid (ADF) detergent fiber, acid detergent lignin (ADL), and in vitro organic matter digestibility (IVOMD). Highly significant (P 60%), considerable (45%) for HI and straw N (40%), moderate for ADL (18%), and minor for NDF, ADF, and IVOMD ( Across all cultivar types only ADF was significantly (P 0.05) relationships were observed between N, ADF and IVOMD and SY. Among cultivars consistent relationships were only observed between N and GY which were significantly (P = 0.03 to 0.009) inversely correlated in five out of the six cultivar types. Within cultivars types ADF varied by at least 2.3% units in HTNM and 1st DRYT and up to 4.9% units in ESWYT. By extrapolation such cultivar-dependent differences will matter at wheat straw trading.

High throughput phenotyping of canopy senescence based on Normalized Difference Vegetation Index (NDVI) could be useful in plant breeding. The aim of this paper was to assess the association between grain yield and canopy senescence quantified with NDVI in oat lines selected for grain yield and milling quality. Sixteen lines were grown in four winter-rainfall environments where logistic curves between NDVI and thermal time from anthesis (GS60) were fitted to return five traits: maximum NDVI, NDVImax; minimum NDVI, NDVImin; thermal time to 50% senescence, x50; rate of senescence, rate; and the area under the NDVI curve, area. Across sources of variation, residuals of yield after removing the effect of phenology correlated with area (r = 0.69), NDVImax (r = 0.67), x50 (r = 0.57), NDVImin (r = 0.51) and rate (r = −0.30), all significant at P

International audience; Soybean is prone to weed infestations and yield variability. With the proposition of using intercropping to overcome these problems, this study explored the effects of combinations of different associated crop species and spatial arrangements on grain production and weed control.In a two-year field experiment in western France, soybean was intercropped with buckwheat, lentil, sorghum and sunflower in two spatial arrangements: within-row intercropping and alternate-row intercropping, to investigate their effects on weed control and soybean production.The results showed that the highest soybean yield occurred in the intercropping with lentil, followed by sorghum and sunflower, and finally buckwheat, but this effect varied by year. The opposite species order was obtained for weed control, revealing a trade-off between soybean production and weed control. We also demonstrated that associated species height was related to soybean yield and weed control. Alternate-row intercropping helped to increase soybean production without compromising weed control for sorghum and buckwheat, which have small height difference with soybean.Finally, our paper showed that combining associated species choice and spatial arrangement allows farmers to manage the trade-off between soybean yield and weed control.

Reducing the fertiliser nitrogen (N) requirement of oilseed rape (Brassica napus L.) whilst maintaining yield will be beneficial for both growers and the environment. The aim of this paper was to identify differences in fertiliser N requirement between varieties and investigate simple in-field methods to rapidly identify varieties that can maintain high yield whilst requiring lower optimal N rates (‘HYLO’ varieties) to aid breeding for lower N fertiliser requirement. Four field experiments were conducted in the UK during seasons 2011-12 or 2012-13 on a range of soil types. Each experiment included 21 elite open pollinated and hybrid varieties. Each variety was grown at seven levels of N fertiliser ranging from zero to super-optimal (340 or 400 kg N/ha). Measurements of seed yield and seed oil content were combined to calculate gross output yield, i.e. seed yield adjusted for oil content. Linear plus exponential yield response curves were fitted to calculate the economically optimum N rate (Nopt) of each variety and the associated nitrogen use efficiency (NUE) was calculated at the Nopt. Across varieties, gross output yield responses to optimum N fertiliser, compared with yields at nil N rates, were significant, ranging from 1.3 to 2.7 t/ha between sites. Nopt ranged from 117 to 286 kg N/ha between sites giving experimental average yields at Nopt (Yopt) of 3.0 to 4.6 t/ha. Varietal yield ranges at Nopt within each experiment ranged from 0.6 to 1.7 t/ha, and there was a positive trend for yield to increase with date of variety introduction by 0.24 t/ha per decade. Significant variety x N fertiliser rate interactions were measured for gross output yield in two out of four experiments and significant varietal differences in Nopt were measured in one experiment ranging from 195 kg N/ha to 296 kg N/ha. There was no correlation between Nopt and Yopt indicating that improving varietal yield potential will not necessarily increase N requirement. Significant varietal differences in NUE were measured at Nopt ranging from 13.5 to 15.9 kg of gross output yield per kg of N supply from soil residues and fertiliser. Seed with low N and high oil content, and high biomass harvest index could be useful indicators of high NUE. However, no single trait correlated consistently with varietal variation in NUE. The yield difference between sub- and super-optimal N rates was positively correlated with Nopt. Further research is required to develop new experimental approaches for measuring yield at more than one N level on small experimental plot areas and to investigate a wider range of genotypes.

The correction of soil fertility constraints is necessary for the successful production of sugarcane. Inhibition of potassium (K) uptake by sugarcane plants in the presence of high concentrations of calcium (Ca) and magnesium (Mg) has been reported, with some sugarcane-growing countries adjusting K fertiliser recommendations accordingly. Although the depressive effect of K on Ca and Mg uptake is well documented for other crops, this phenomenon has not been widely recognised in sugarcane, and is not taken into account when making Ca and Mg recommendations. The interactions between K, Ca and Mg were therefore investigated on two contrasting soil types (Oxisol and Inceptisol) on the east coast of KwaZulu-Natal, South Africa, in factorial-designed field trials. Trials at each site included the plant crop (first crop after planting) and two ratoon crops (crops which regrow following harvest). This paper deals with the impact of the treatments on leaf nutrient levels and crop yields. Potassium treatments (0, 100, 200 and 300 kg K ha−1, as KCl) resulted in significant (P

Seasonal dynamic of forage quality and yield has a major impact on livestock production. A sound evaluation on quality and quantity of forage is useful for cost-effective utilization of forage. However, forage quality and yield can vary with forage species, harvest seasons and yearly climate conditions. To improve forage use efficiency, a field experiment (2008–2010) was conducted in Swift Current, Saskatchewan, Canada. Dry matter yield and quality indicators (fiber, protein, digestibility and minerals) were measured for nine cool-season grasses harvested in June, August and October. The interrelationships and attributes among quality indicators were determined by principal component analysis (PCA) and the weights of quality indicators were calculated by entropy weight (EW) method. To synthesize different attribute indicators into a comprehensive index that reflects quality ranking of different forage species, an integrated multi-index decision analysis method, i.e., PCA-based TOPSIS with EW, was used in this paper. The evaluation process and results showed that the interrelation patterns and positive or negative attributes for quality indicators were consistent with years and harvest seasons, whereas the rankings of most grasses in yield and comprehensive quality varied with years and harvest seasons. According to the yearly and seasonal rankings of forage quality and yield, flexible production tactics and adaptive management techniques should be considered within the western Canadian prairie region. For instance, Northern wheatgrass (Agropyron dasystachyum) can be recommended to be mixed with high quality forages due to its high yield in any harvest season. Meadow bromegrass (Bromus Riparius) can be recommended to be mixed with high yield forages due to its high quality in summer and fall. These findings will provide valuable information for forage breeders, and livestock and forage managers to maximize grass utilization efficiency while balancing yield and quality.

Lack of irrigation water for flooded cultivation and low temperature during the reproductive phase are factors limiting rice production in the Riverina region of New South Wales, Australia. While cold tolerant genotypes are available for flooded conditions, the consistency of cold tolerance under different growing conditions including non-flooded conditions remains unknown. The objective of this paper was to determine genotypic consistency in cold tolerance under different water and soil nutrition conditions. Three experiments were conducted in which genotypes from a Kyeema//Kyeema/Norin PL8 population were exposed to low air temperature (21/15 °C day/night) for 14 days at the booting stage. Genotypic variation in spikelet sterility existed within the population and the ten most tolerant (22.8%) and susceptible (73.2%) genotypes were identified. Generally, the genotypes grown under non-flooded conditions and low temperature ranked similarly to those in the flooded and low temperature (r = 0.90**), with tolerant genotypes consistently identified as tolerant even under high nitrogen flooded (r = 0.97**) conditions. N application increased tillering and spikelet number per plant, leading to increased spikelet sterility under low temperature. Spikelet sterility negatively correlated with grain yield/plant but some genotypes with low spikelet sterility also had low grain yield, due to inherently low spikelet number per panicle. The genotypic consistency in cold tolerance under different growing conditions suggest that it may be possible for genotypes to be screened for low temperature tolerance under flooded conditions and identify genotypes appropriate for use in non-flooded conditions, thus minimising resources required to screen for low temperature tolerance and non-flooded conditions in a two-step process. However, to confirm this, testing in the field with larger population numbers from diverse genetic backgrounds is required.

Dual-purpose crops are grazed during the vegetative phase by cattle, goats and sheep in many dryland farming systems. After grazing, these crops continue to grow until maturity when they are harvested for grain. The process of grazing depletes crop nitrogen (N) content. Yield and grain protein concentration may therefore be more N-limited in grazed than in grain-only crops. This paper reviews 14 field experiments in south-eastern Australia, 12 of which were on farms, to measure the responses to N fertilizer by wheat, barley or canola crops defoliated by mowing or grazing with sheep. In five experimental comparisons of defoliated and grain-only crops, the average nitrogen use efficiency (NUE) of fertilizer N applied soon after defoliation, as is typically practiced, was 18 %, while NUE of grain-only crops fertilized at the same time and N-rate was 41 %. Applying N fertilizer to defoliated crops at this stage was usually unprofitable. In one experiment comparing responses of grazed and grain-only crops to time of N application post-grazing, a delay of two weeks after grazing increased yield of grain-only crops and NUE of both grazed and grain-only crops, compared with application soon after grazing. Our explanation of these results is the low N demand by small, defoliated crops and increased N demand as they regrew after defoliation. Additional evidence for the N-demand explanation came from a positive relationship between NUE of grazed crops and the yield of grain-only crops. The results suggest that delaying N application for two weeks after grazing and retaining more biomass after grazing can increase N demand, yield and NUE of grazed crops.

Genetic improvement has been given high priority in rice research for development in sub-Saharan Africa (SSA). This paper provides an overview of historical efforts of genetic improvement in SSA focused on improving rice productivity. It further describes yield gain of new rice varieties evaluated in recent field experiments in four selected breeding target domains, and summarizes adoption studies on rice varieties. Efforts to develop rice varieties adapted to diverse rice production systems in SSA have been made by several research organizations, including national agricultural research institutes, bilateral organizations, and three CGIAR centers. The efforts have resulted in the release of around 570 rice varieties in 10 major rice-producing SSA countries by 2020. Among these varieties, the most well-known are interspecfic upland rice varieties “New Rice for Africa (NERICA)” that were developed from crosses between improved Oryza sativa tropical japonica and Oryza glaberrima varieties. However, recent field assessements demonstrated that upland rice yield can be further improved through introduction of upland indica materials from Asia. In contrast, lowland interspecific rice varieties out-yielded the previously released improved O. sativa varieties in selected SSA countries. Field assessments in Senegal and Madagascar did not demonstrate the yield advantage of the recently-developed varieties including hybrids over best performing ones released before. The adoption level of improved varieties in terms of share of area occupied by improved varieties in 18 SSA countries was 40 % in 2008 with old varieties that were released before 2000 being dominant and 7% of the total rice area occupied by NERICA varieties. Especially in irrigated and rainfed lowland rice systems, the majority of dominant varieties were still those introduced from Asia. Panel data between 2002 and 2019 from the Senegal River Valley also confirmed this, and Sahel 108, which was introduced from Asia and released in Senegal in 1994, accounted for >70 % of the total rice area in both the wet and dry seasons in 2019. The implications of this review for future rice genetic improvement and varietal replacement in SSA are discussed.

The use of controlled release fertilisers (CRF) is being promoted in the Australian sugarcane industry to improve nitrogen (N) use efficiency and reduce N losses through better matching of N release with crop N demand. Little is known, however, about the required synchrony due to limited information on both N uptake patterns of sugarcane and N release patterns from CRF under different crop growing conditions. This paper uses APSIM scenario modelling to characterise N uptake patterns of sugarcane plant and ratoon crops in response to seasonal variability and different climatic and management conditions (e.g. level of water and N input, time of planting/ratooning) at five sites within the Australian sugarcane growing region. The results showed considerable variations in crop N uptake patterns across seasons, sites and under different management scenarios. However, for a given site, crop N uptake patterns during the early crop growth stage varied little between seasons (

Frost, during reproductive developmental stages, especially post head emergence frost (PHEF), can result in catastrophic yield loss for wheat producers. Breeding for improved PHEF tolerance may allow greater yield to be achieved, by (i) reducing direct frost damage and (ii) facilitating earlier crop sowing to reduce the risk of late-season drought and/or heat stress. This paper provides an economic feasibility analysis of breeding options for PHEF tolerant wheat varieties. It compares the economic benefit to growers with the cost of a wheat breeding program aimed at developing PHEF tolerant varieties. The APSIM wheat model, with a frost-impact and a phenology gene-based module, was employed to simulate direct and indirect yield benefits for various levels of improved frost tolerance. The economic model considers optimal profit, based on sowing date and nitrogen use, rather than achieving maximum yield. The total estimated fixed cost of breeding program was AUD 1293 million, including large scale seed production to meet seed demand, with AUD 1.2 million year −1 to run breeding program after advanced development and large scale field experiments. The results reveal that PHEF tolerant varieties would lead to a significant increase in economic benefits through reduction in direct damage and an increase in yield through early sowing. The economic benefits to growers of up to AUD 4841 million could be realised from growing PHEF tolerant lines if useful genetic variation can be found. Sensitivity analyses indicated that the benefits are particularly sensitive to increases in fixed costs, seed replacement, discount rate, and to delays in variety release. However, the investment still remains viable for most tested scenarios. Based on comparative economic benefits, if breeders were able to develop PHEF tolerant varieties that could withstand cold temperatures −4 °C below the current damage threshold, there is very little further economic value of breeding total frost tolerant varieties.

ORYZA version 3, as the successor to ORYZA2000, is an ecophysiological model that can simulate rice growth and development for targeted yield with different nitrogen (N) fertilizer rates and planting densities in a given rice production system. Currently, there is little published information on the application of ORYZA (v3) and ORYZA2000 in simulating high-yielding rice cultivars under different N rates and planting density schemes in central China. This paper combines field experimentation with ORYZA (v3) to calibrate the crop growth characteristics of widely grown high-yielding inbred and hybrid rice cultivars. The calibrated model was applied to simulate yields under different N rates, planting densities, and seedlings per hill, using historical weather data from 1986 to 2015. ORYZA (v3) reliably simulated the dynamics of crop biomass and leaf area index, and seasonal yield, with relatively small normalized root mean square error (RMSEn) and high adjusted linear correlation coefficient (R2), but slightly over-estimated leaf N concentration. Scenario analyses indicated that the maximum differences in simulated yields were 72.1 kg ha−1 due to planting density, 112.8 kg ha−1 due to seedlings per hill, and 3266.2 kg ha−1 due to N rates. The simulations demonstrated that further field experiments are crucial in investigating the effects of rice genotype, N management and their interactions on yield for optimal crop management.

In order to understand the regulation of source-sink relationship on leaf senescence in maize, we investigated the effect of pollination prevention on leaf senescence, post-silking dry matter and nitrogen accumulation and remobilization in different vegetative organs in one landrace and ten representative maize hybrids released between 1973 and 2000 in China. When pollination was prevented by covering silk with paper bags at silking stage, leaf senescence of Nongda 60, Yedan 13, Shendan 7 and Zhengdan 958 was delayed as shown by the remaining green leaf area per plant at maturity. However, pollination-prevention did not have obvious effect on the leaf senescence of Baimaya, Danyu 6, Yedan 2 and Xianyu 335. By contrast, pollination-prevention accelerated the leaf senescence of maize hybrids Zhongdan 2, Danyu13 and Yedan 4. It was found that leaf senescence of the late-released (since 1985) Chinese hybrids tended to be delayed by pollination-prevention, except XY335. From silking to physiological maturity, nitrogen content increased in the stem (plus the sheath, cob, husk, and tassel) and root of the non-pollinated plants. However, there was still a net reduction in leaf nitrogen content. We also found that pollination-prevention reduced leaf nitrogen remobilization efficiency, with genotypic difference and variation between the two years of testing. The results suggested that the response of leaf senescence to pollination-prevention is at least partially due to the change of leaf nitrogen remobilization efficiency. Leaf senescence tended to be delayed if leaf nitrogen remobilization efficiency is highly reduced by pollination-prevention.

Maintaining grain quality of wheat under climate change is critical for human nutrition, end-use functional properties, as well as commodity value. This paper reviews the current knowledge of high temperature and elevated atmospheric CO2 on whole-grain and functional properties of wheat. It also considers the utility of contemporary crop models for investigating the impacts of climate change on wheat quality; and discusses opportunities for advancing model capability. Under elevated CO2 wheat yield can increase by up to 36%, but universally grain protein concentration decreases and a shift in composition translates to reduced functional properties. High temperature during the post-anthesis period of crops can cause a step change reduction in grain-set, grain size and milling yield. Numerous crop models including APSIM-Nwheat, CropSyst, Sirius, GLAM-HTS account for high CO2 effects through modification of RUE, TE or critical leaf-N concentration and high temperature by accelerated leaf senescence, grain number, potential grain weight or HI modifications. For grain quality, however, crop models are typically restricted to predicting average grain size and grain-N content (concentration), although the SiriusQuality model accounts for the major storage proteins, gliadin and glutenin. For protein composition, high temperature stress reduces the glutenin/gliadin ratio and limits the synthesis of the larger SDS-insoluble glutenin polymers which causes wheat dough to have weaker viscoelasticity properties. This link provides an opportunity to model high temperature effects on grain functional properties. Further development and testing, utilizing grain quality data from global FACE programmes will be particularly valuable for validating and enhancing the performance of such models. For whole-grain characteristics, a single-spike model approach, which accounts for intra-spike variation in assimilate deposition may provide an opportunity to predict grain size distribution and associated screenings percentage and milling yield. Taken together expanding the predictive capability of our crop models to grain quality is an important step in providing a powerful tool for developing adaptation strategies for combating the impacts of climate change to global crop production and grain quality.

An understanding of genotype × environment (G × E) interactions for phenological adaptation in crops can help identify traits that facilitate genetic improvement and cultivar selection. Such understanding is also necessary to identify environments that facilitate identification of cultivars with better environmental adaptation. Process-based crop simulation models including APSIM are valuable tools to investigate G × E interactions and traits conferring adaption to particular conditions. However cultivar parameters relating to crop phenology in crop model are difficult to determine directly through field experiments. Within this paper, we present a simulation study to explore the environmental and genotypic control of time to flowering and maturity in lupin and its grain yield, by using the APSIM model. In the model, lupin cultivar parameters were optimized by combining prior knowledge and PEST (Parameter ESTimation), a model-independent parameter optimiser. The parameterisation was for nine lupin cultivars with contrasting maturity (early vs late) and vernalization requirement (non-responsive vs responsive) across 13 sites × years across Australia. We showed that phenological differences among the cultivars were well explained by the optimized set of parameters, mainly reflected in vernalization response and photoperiodic sensitivity before flowering. Simulated flowering days and grain yield agreed well with the observations, with RMSEs (root mean squared error) of 4 days and 0.34 t ha−1 for all cultivars together. The simulation results showed that lupin yield was significantly affected by temperature and water availability. An early-maturity cultivar would yield better than the late-maturity one at the warm and low rainfall region, while at high rainfall or long-season regions, cultivar types should be chosen tactically based on the climatic conditions for that season. Thus, lupin breeding in Australia should therefore focus on temperature regimes and rainfall gradients. These results indicate that the parameter-optimized APSIM model could be used to explore the adaptation of genotypes to a particular environment to provide guidance for a more efficient breeding program and develop optimal agronomic management practices.

Natural selection does not lead to optimal solutions due to trade-offs and environmental variation, genetic and developmental constraints, and historical contingency. In this paper we propose that constraints like these also often apply to the improvement of both crop varieties and management practices, creating a dual biological and agronomic barrier for the optimisation of crops. We discuss constraints on optimisation of 1) crop ancestors, by natural selection, 2) crop traits, by artificial selection and biotechnology, and 3) crop management. We outline how trade-offs and environmental variation make single-factor optimisation (e.g. “optimum leaf angle” or “optimal fertiliser rate”) impossible. Definitions of “optimal” that recognise trade-offs and variability can help, but we argue there are major constraints on even those forms of optimality. Optimality theory may be useful to formulate null hypotheses, however, as divergence between actual traits and theoretical optima can highlight constraints that are biologically interesting and agronomically relevant. Understanding the nature and size of these constraints can help us map more likely pathways for future improvements in agriculture.

Senescence in cotton is a gradual deterioration process that terminates plant growth and development and ultimately leads to plant death. Maturity performance refers to the senescence appearance of cotton during the boll-opening stage, which is the manifestation and result of senescence. Maturity performance categories include premature senescence, late maturity and normal maturity. Premature senescence and late maturity are anomalies of cotton growth caused by genotype and environment interactions. They result from differential expression of a large number of senescence-associated genes during late growth and development stage. In this paper, we review and summarize research progress on the physiology, ecology, and molecular basis of cotton senescence and maturity performance. Strategies for achieving normal maturity performance with maximum cotton yield and quality should include development of optimized varieties, rational application of plant growth regulators, and use of agronomic measures to regulate cotton growth, development and senescence.

In our previous study, an early season rice restorer line B2A68 expressing Cry2Aa# gene was obtained. In order to evaluate the performance of B2A68’s hybrids, a total of six hybrids from crossing B2A68 with six thermo-sensitive genic male sterile (TGMS) lines of early season rice were compared for expression level of Cry2Aa protein, as well as in insect resistance, agronomic traits and grain quality with their non-Bt null controls. Our results showed that the highest Cry2Aa protein content among B2A68's hybrids was detected in leaf, where the Cry2Aa content was nearly three times of that in stem. The Cry2Aa content of B2A68 was significantly higher than those of its derived hybrids, indicating the Cry2Aa# gene was incompletely dominant in hybrids. The hybrids with Cry2Aa# gene exhibited higher plant protection against rice leaf roller than the hybrids without Cry2Aa# gene in field. Significant differences were observed in plant height, panicle length, number of grains per panicle, seed set, 1000-grain weight and yield per plant between hybrids with Cry2Aa# gene and hybrids without Cry2Aa# gene in 2013 or 2014. There were significant differences in chalky grain rate and chalkiness degree between paternal lines B2A68 and D68, and between hybrids with Cry2Aa# gene and hybrids without Cry2Aa# gene. All of the differences in agronomic traits and grain quality varied among parental lines and hybrids. In this paper, three hybrids with high lepidopteran resistance, high yield, elite agronomic traits and acceptable grain quality was selected out, that could serve as elite resistant hybrids to control lepidopteran pests in early season rice production.

In a previous paper (Field Crops Res. 203, 114-127), we showed that the difference in yield potential between a contemporary and a traditional cultivar was due to differences in fruiting efficiency, likely derived from differences in spike fertility (fertile florets per spike) while having similar spike dry weights at anthesis. In this study, we determined the mechanistic bases of these genotypic differences in spike fertility analysing the initiation of all floret primordia per spike (up to 8), the maximum number of florets initiated per spikelet, and the associated floret developmental rates and their fate to become fertile florets under contrasting photoperiod (natural vs extended) and nitrogen availability (50 or 200 kg N ha−1) during the stem elongation phase. Under potential growing conditions (natural photoperiod, high nitrogen availability), the contemporary cultivar owed its higher spike fertility to the improved rate of floret development, which mainly determined an improved level of floret primordia survival to produce fertile florets. The sensitivity of the floret developmental patterns to faster development due to exposure to an extended photoperiod and, to a larger extent, a reduction in N availability was similar for both cultivars, providing a basis for the consistent differences in spike fertility across a range of environments. The response again determined a main effect through increasing floret mortality reducing therefore the level of fertile florets per spikelet in these conditions. Funding was provided by project AGL2009-11964 granted by the Spanish Ministry of Science and Innovation. AF held a FPU scholarship from the Spanish Government.

Growth and reproductive structure retention in cotton (Gossypium hirsutum) is dependent on light intensity, which is often irregular in tropical environments due to shading from cloudiness associated with the monsoon. The objective of this study was to evaluate the potential effects that cloudiness-induced reproductive organ abscission and compensatory responses might have on cotton growth, partitioning and conversion of radiation to biomass (radiation use efficiency RUE) as this was unknown for the monsoon tropics. Cotton cultivars representing different morphology were sown in field experiments at closely timed intervals during the early monsoon over 5 seasons to expose crops to varying amounts of cloud-related shading, creating a matrix of crop responses. In paper I, final boll number was strongly linked with lint yield, and boll retention on the early and late flowering sympodia and yield were correlated with the radiation environment during flowering. Grouping sowing time treatments that had a similar intra-canopy distribution of bolls at maturity provided a mechanism to compare yield recovery post boll loss and consider causal factors. Maximum crop biomass ranged from 1232−1933 g m−2. Lint yield was correlated with the fraction of total biomass present as bolls (P Differences in biomass partitioning between cultivars were minor. When cloud cover abated, extended concurrent vegetative and reproductive growth enabled yield recovery. Greater LAI was a consequence of compensatory processes following fruit loss. Faster development of LAI in response to the monsoon during early flowering could further shade lower canopy fruiting sites, exacerbating fruit abscission and impacting yield compensation. RUEg (glucose equivalent) of 2.35 & 2.63 g MJ−1 PAR was comparable with cotton grown in temperate environments but declined when lower canopy fruit abscission followed by extended concurrent growth altered the ratio of vegetative vs reproductive biomass partitioning. Cloudiness poses a dichotomy of challenges for crop management during the tropical monsoon season. After cloudiness-induced fruit loss, extended concurrent growth when the radiation environment improves must be encouraged to enable the initiation of new fruiting sites for yield recovery. However, expansionary canopy growth in response to cloud and fruit loss may exacerbate detrimental shading of the lower canopy and detract from later yield recovery. Therefore management tactics including the use of irrigation, nutrient and growth regulant inputs must achieve an appropriate balance between vegetative and reproductive components during compensatory growth.

There is considerable interest in assessing genetic gain from breeding efforts, as well as trends from non-genetic sources such as climate change. Long-term data from official variety trials provide an ideal opportunity to do so. Whereas past work on the subject was mainly focussed on trends in mean performance, little attention has been paid to yield stability. The purpose of the present paper therefore is to provide a framework for assessing trends in stability and to exemplify this using long-term data from German variety trials. Specifically, trends in the mean and variance of winter wheat and winter rye yields associated with genotypic, spatial, and climatic covariates were investigated based on a long-term series of multi-environment trials from 1983/1985 to 2016. Yield stability is assessed based on the variance of yield. For climatic covariates, trends were investigated using growth stage-specific covariates which were obtained by dividing the total growth period into five or ten growth stages within which covariates were aggregated. The analysis was done by linear mixed models and forward selection served to identify trends in mean and variance. Specifically, trends in the mean were selected based on a coefficient of determination, R 2 , while variance trends associated with a covariate were selected based on the change in variance attributable to the covariate. For spatial covariates, mean yield increased with the field capacity in up to one meter soil depth in case of rye. For both crops, mean yield was negatively affected by a deficit in available water during the development of vegetative parts while water deficit towards the end of the growth period was positively associated with mean yield. Trends were also selected accounting for interactions of climatic covariates and genotypic groups (wheat: quality type; rye: breeding type), revealing that R 2 generally increased when interactions were taken into account. The responses to covariates were similar for the different groups, meaning the increase in R 2 is mainly attributable to the main effects of the genotypic groups. Variance trends associated with the calendar year were identified for both crops, revealing yield variance slightly increased with time. Based on the selected model, a coefficient of variation was obtained for each year to assess relative yield stability, showing a decrease for wheat and an increase for rye.

Improving grain yield and adaptation is achieved by synchronising crop phenology with the environment. Phenology research is complex and encounters analytical challenges in characterising genotype x environment (GxE) interactions. This paper presents a simple approach that helps to explain the environmental drivers of phenology. Photoperiod and temperature are major environmental cues for expression of crop developmental genes, and sensitivity to photoperiod is thought to be the major cause of maturity differences among Australian spring barley varieties. However, temperature and photoperiod show similar seasonal trends and strong autocorrelation makes it difficult to distinguish their relative importance in crop development. Partial Least Squares regression (PLS) was developed to handle large data sets with many correlated explanatory variables and only one dependent variable. Across 35 environments encompassing a wide range of temperature and photoperiod regimes in southern Australia, a PLS model described more than 90 % of the phenotypic variation in time to anthesis of three adapted barley cultivars. The PLS outputs defined the critical periods when photoperiod and temperature were most influential, and revealed that temperature effects are of equal or greater importance than photoperiod in determining anthesis date, which is a new finding for genotypes adapted to Australian environments. Insight into the previously elusive differential responses to changes in daily average, maximum, and minimum temperatures will assist in developing flowering models for growers that are more accurate, and assist breeders in the genetic dissection of phenology for target environments.

Machine transplanting is an alternative establishment method to replace manual transplanting that reduces labor inputs in rice production. It is important to reduce the seed rate in mechanical transplanting, especially for hybrid rice with expensive seeds. Printed sowing (PS), i.e. pasting seeds to paper, is a new sowing method for reducing the seed rate. This study was conducted to compare seed rate, grain yield, and yield attributes in machine-transplanted hybrid rice between PS and manual sowing (MS). Field experiments were conducted in the early and late seasons of 2017 and 2018 in Yongan Town, Hunan Province, China. Seed rates under PS were 9.6–19.8 kg ha–1, which were lower by 2.73–5.65 times than under MS. PS produced 11 % higher grain yield compared to MS. The higher grain yields under PS compared to MS were mainly due to higher seedling quality, larger panicle size, higher spikelet filling percentage, higher aboveground biomass, and higher harvest index under PS than under MS. The better performance of yield attributes under PS compared to MS could be explained by improvements in morphological and physiological traits including number of vascular bundles and leaf photosynthetic capacity. Our study suggests that PS is a feasible method to reduce seed rate and increase grain yield in machine-transplanted hybrid rice production.

Yield potential studies can assist in identifying the production constraints in any cropping system and economics at the farm level dictate a continual need to increase yield and profit for most crops. Cotton is a tropical indeterminate perennial grown as an annual crop for fibre (lint), oil and meal for animal feed. Its growth habit means a production season can have a long duration up to 180 days. Here we define yield potential as yields that can be obtained with current cultivars and systems under ideal conditions in the absence of poor weather, disease, soil or nutritional constraints with management and genetics optimised. This paper aims to review yield potential in cotton and particularly identify factors, such as climate, soil health, nutrition, water, weeds, pests and diseases which affect yield. Worldwide, average cotton lint yield is about 800 kg/ha and is increasing at rates of 10–20 kg/ha/year, especially where irrigation is available. Under irrigated conditions, lint yield of 3500 kg/ha is now being obtained and we use this value for yield potential under full season irrigated conditions. Yield potential for raingrown cotton production systems depends on soil water storage and rainfall but is about 800 kg lint/ha. Thus, yield potential is not a fixed value but it is increasing through time as crop management and genetics are improved—but it is also strongly affected by local conditions. We derived the theoretical yield of cotton from potential growth or photosynthesis and respiration rates by growth analysis, from radiation use efficiency or by simulation modelling. All three methods indicated theoretical yield to be about 5000 kg lint/ha. To achieve this yield, a long season is required, possibly with slower initial fruit set so canopy size is not restricted by high fruit load. Estimates of resource requirements for lint yields of 5000 kg/ha indicated that nutrient uptake of 384 kg/ha N and K and 83 kg P/ha would be a more challenging constraint than the 10.7 Ml/ha of total evapotranspiration required. Future research opportunities were identified in crop agronomy (nutrient uptake and use efficiency), plant physiology (modelling fruiting dynamics), breeding (longer season plant types with slower initial fruit setting) and biotechnology (increased photosynthesis).

Lodging lowers the productivity of sugarcane through a reduction in radiation use efficiency and stalk damage. However, there are few reports of experiments specifically designed to quantify effects of lodging in sugarcane. Efforts to model onset and progression of lodging, and the impact on crop productivity, have not been attempted. The objectives of this paper were to quantify effects of lodging on sugarcane and to develop modeling capability in terms of predicting lodging onset, progression and impact. Field experiments with irrigated ratoon crops were conducted at Pongola, South Africa. In one treatment the cane in each plot was allowed to grow through bamboo frames that prevented lodging. In the other treatment, the cane was not supported and could lodge at any stage. The degree of lodging was captured weekly by a rating that ranged from 1 to 9, where 1 = fully erect cane and 9 = completely lodged cane. At harvest estimated recoverable crystal percent (ERC %) of stalks and yield (cane and ERC) was measured for each plot. Lodging resulted in decreased ERC yields of up to 20.6%. An algorithm for simulating lodging when aboveground biomass (including rainfall and irrigation water retained on it) exceeds a variety-specific threshold, and which also considers wind speed and soil water content, was evaluated for predicting the extent and impact of lodging in the Pongola experiments, as well as for four deficit irrigation treatments of a field experiment conducted in Komatipoort, South Africa. The study showed that the onset of lodging was simulated reasonably well for various soil/crop/atmospheric conditions, while the extent of lodging at harvest was simulated very accurately for all crops. Simulated lodging was primarily driven by crop size and lodging events were triggered by rainfall that added weight to the aerial mass of the crop, and reduced the anchoring ability of the soil through saturation of the top soil. More accurate simulation of lodging, and its impacts on yield, will improve the accuracy of yield predictions by crop models, increasing their value in applications such as crop forecasting, climate change studies and exploring crop improvement and management options.

Wheat has been cultivated in China for at least 4000 years, but it took until 1914 in Nanjing before crossbreeding programs commenced. Wheat breeding has made substantial contribution to China's wheat production capacity over the years. Data on more than 1850 Chinese wheat varieties from the 1920s to 2014 (categorized into north winter wheat, south winter wheat and spring wheat varieties) were collected in order to (1) better understand progress in agronomic performance, (2) analyze the evolution of yield-related traits, and (3) formulate strategies for future breeding. Since the 1920s, average grain yield has increased annually by 1.29% for north winter wheat, 1.5% for south winter wheat and 0.52% for spring wheat. For north and south winter wheat, kernel number per spike and 1000-kernel weight (TKW) have increased significantly, with no change to spike number per unit area. Spike number per m2 has not changed significantly in any of the three major agro-ecological production zones. Average plant height of north winter wheat declined from the 1950s to 2000s to stabilize at 80 cm; south winter wheat declined from the 1930s to 1990s to stabilize at 86 cm; and spring wheat decreased from the 1960s to 1990s to stabilize at 89 cm. Seedling density in both north and south winter wheat has significantly reduced, with no significant changes for spring wheat. Variability of varieties in yield and agronomic traits has declined since the 2000s. Breeding programs for wheat varieties have contributed to food security in China. Yields for north and south winter wheat have steadily increased since the 1920s, following the rule of thumb to increase TKW and kernel number per spike without changing spike number per unit area. For spring wheat, average grain yield has increased annually significantly since the 1920s, and reached its peak in the 1980s but has since decreased. Future increase in yield may be achieved through improvement in kernel size and kernel number per spike. This paper comprehensively evaluates the historical development of wheat varieties in three main agro-ecological regions of China, and will act as a guide for future wheat breeding and production technology.

Night temperature (NT) increases faster than day temperature with global warming and this may have strong implications for crop yield. One of the assumptions is the increase in night respiration and thus the increase in carbon losses over time. Some rice cultivars (indica, aus and japonica types) were grown in the field in the Philippines and in heated greenhouses in Montpellier, France, to quantify the response of respiration to increased NT and its implication at crop level. Increased NT by 3.8 and 5.4 °C over the whole crop cycle in two greenhouse experiments and by 1.9 °C in the field from 33 days after transplanting up to maturity using a free-air-controlled enhancement increased night respiration rate significantly. Overall, the cost in CH 2 O of night respiration over crop duration was 17 to 20% (field) and 8 to 18% (greenhouse) of the potential shoot dry matter (including that lost by respiration). Additional respiratory burden due to increased NT was only 1 to 7% of the potential shoot dry matter at maturity, and was not associated with significant loss in additional dry matter. The absence of any dry matter reduction with increased NT within indica cultivars questions the assumptions of recent papers.

Rice is one of the most important cereal crops, feeding more than 50% population of the world. To meet the demand of increasing population, rice production has to be improved continually. As a very important part of rice plant, root system plays multiple roles in rice growth: anchorage of the plant, acquisition of water and nutrient elements, and biosynthesis of amino acids and hormones, etc. Almost all of the hot spots about rice research are associated with rice root: drought tolerance, lodging resistance, and efficient use of nutrition, the goal is to increase the grain yield with desirable seed quality. Although the understanding about rice root has been expanded in the last decades, there remain much to be done about root morphology and physiology, especially in root genetics. Rice root research is an exciting and focusing field in recent years. More and more researches on rice root genetics have been made. There is a close relation between above ground traits and underground roots, providing an alternative approach for rice genetic improvement. A number of genes associated with root architecture and physiological functions have been identified, or cloned. It provides an opportunity to further improve rice based on molecular assisted selection. Root traits improvement should be taken into account in future breeding programs in rice. However, root research is still a consuming and difficult work, because it was largely influenced by the complex underground environment. This paper reviewed the progress in rice root genetic research, and discussed its prospects.

The main objectives of this paper were to explore effective ways of improving the lodging resistance of high-yield rice populations and the lodging resistance capacity responses of different rice populations to nitrogen. Field experiments were conducted at the following two eco-sites: Taoyuan (a special high-yield eco-site) in Yunnan province and Danyang (representative eco-site of the middle and lower Yangtze) in Jiangsu province, China in 2011 and 2012. A super indica hybrid rice called ‘Y Liangyou 2’ was grown at each eco-site under different N levels. The lodging index at Taoyuan was significant lower than that at Danyang. The heavier dry weight per cm of leaf sheath and higher proportion of cellulose and lignin in the basal stems enhanced the stem strengths at Taoyuan, in spite of the smaller culm diameter and thinner wall thickness. The shorter elongated internodes of the basal stems were responsible for the lower plant height and the height of center of gravity. In addition, the lodging index at Taoyuan was affected significantly by nitrogen. With increasing nitrogen, the plant height, the height of the center of gravity, dry weight per centimeter (cm) of basal stems (culms and leaf sheaths), bending stress and carbohydrate content were more susceptible to nitrogen. At Danyang, the responses of morphological and physiological parameters to nitrogen tended to level off, the lodging resistance was primarily related to the morphological characteristics of the basal stem. These results suggested that an improvement in the lodging resistance of high-yield rice populations could be achieved by the suitable plant height with the optimum configuration of internodes, namely, shorter basal stems and a longer peduncle, and by increasing stem stiffness, which was primarily attributed to higher proportions of structural carbohydrates (e.g., cellulose and lignin) and greater plumpness of the leaf sheaths.