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Atmospheric carbon‐dioxide concentration ([CO2]) is increasing rapidly, but its interactions with nitrogen (N) and phosphorus (P) fertiliser on wheat grain quality are not well understood. We investigated the effects of ambient CO2 (aCO2; ∼410 ppm) and elevated CO2 (eCO2; 760 ppm) on crop harvest index (CHI), nutrient harvest index (NuHI), shoot macro‐nutrient content and grain macro‐nutrient concentration of wheat grown under two contrasting amounts of N (0.5 and 6 mol m−3 NO3− N) and P (10 and 250 mmol P m−3) fertiliser supply (low and optimum, respectively). Our results highlighted interactions between [CO2] and N and P fertiliser supply for the shoot biomass at anthesis and straw biomass at harvest maturity. This was because biomass yield did not respond to CO2 level when fertiliser was deficient. However, shoot and straw yield increased (10.0–‐34.0%) with increasing [CO2] at optimum fertiliser rates. Across experiments, grain yield increased (15.6%) with increasing [CO2], which resulted in grain nutrient concentration decreasing (3.0–‐13.0%) with increasing [CO2]. This was attributed to nutrient 'dilution' due to increased carbohydrate content in the grain. Overall, fertiliser supply impacted crop responses more than CO2 treatments, and the impact was greater under N than P deficiency. This was reflected through conservative values for CHI, thousand grain weight and NuHIs suggesting plants allocated biomass and nutrients at similar rates for vegetative and reproductive organs independent of [CO2]. [ABSTRACT FROM AUTHOR]

Criteria for N diagnostics have been developed for a range of agricultural crops. The Nitrogen Nutrition Index (NNI) is a widely used indicator of N status. The NNI represents the relationship between above-ground N concentration and an estimated critical N concentration (N c ), which is the minimum N concentration allowing maximum crop growth rate at a given above-ground biomass (W). Although the NNI has been determined for a wide range of agricultural crops, the conceptual basis that explains N dilution patterns have not yet been validated in crops with large storage organs such as fodder beet ( Beta vulgaris L. ssp. vulgaris ). In this study, we assessed the validity of the N c and the NNI for fodder beet based on two field datasets with a wide range of N treatments (0–200 kg ha −1 ) and water supply (rain-fed and irrigated) conditions in New Zealand. The N c and NNI concepts were shown to be valid for crops with large storage organs. A pattern of N dilution, similar to other agricultural crops, was represented by N c = 4.9 W −0.52 (R 2 = 0.97) for biomass (W) ranging from 1.1 to 28 t W ha −1 . The dynamics of N dilution was explained by a simultaneous relative increase in the biomass of storage roots, which have the lowest N concentrations, and a decline in N concentration of all organs (leaves, petioles and storage roots) as W increased. The NNI values calculated from the N c curve ranged from 0.6 to 1.74 with relative biomass declining at NNI < 1. Water stressed crops showed luxury N uptake (NNI up to 1.74) highlighting need for careful interpretation of NNI values depending on growth conditions. These results can be used to manage N supply in fodder beet, and to support analysis and modelling of physiological responses to N supply in crops with large storage organs. [ABSTRACT FROM AUTHOR]

Fodder beet is a highly productive forage crop of expanding use in livestock production systems in temperate regions, notably in Europe and New Zealand. The main determinant of fodder beet productivity is the amount of light intercepted by the crop canopy, which is regulated by temperature and the availability of water and nitrogen (N) for plant development and growth. The quantitative understanding of canopy formation processes under constraining growth conditions is an essential step for the development of biophysical simulation models of new crops for research and predictive purposes. In this study, we provided the first estimates of key canopy formation parameters in fodder beet both under optimum and water- and N-limited supply, in two field experiments in Lincoln, Canterbury, New Zealand. Specifically, the base temperature for leaf appearance in fodder beet was estimated as 0 °C. The range of the critical LAI (c. 90–95% of light interception) was 3–4 m 2 /m 2 . The phyllochron was 48–53 °Cd/leaf in unstressed crops and 60 °Cd/leaf in water stressed crops, with no effect of N supply. Leaf senescence rates varied widely (from 42 to 260 °Cd/leaf) depending on water availability and canopy cover. Leaf expansion, appearance and senescence rates fully recovered following a period of water stress to values similar to those observed in unstressed crops in response to late season rainfall events. Leaf area expansion rates (LAER) ranged from 0.0012 to 0.0034 m 2 /m 2 /°Cd and was reduced both by limited water and N supply. Leaf area senescence rates (LASR) ranged from 0.0005 to 0.0019 m 2 /m 2 /°Cd, with low values recorded during drought periods when crop growth was negligible. Canopy architecture, characterised by the extinction coefficient ( k ), was less sensitive to water stress than canopy expansion or senescence with a conservative value of 0.74. This first quantitative description of fodder beet canopy forming processes can assist the development of predictive approaches, such as biophysical simulation models, for application in research, extension and teaching. [ABSTRACT FROM AUTHOR]

Crop growth is related to radiation-use efficiency ( RUE), which is influenced by the nitrogen ( N) status of the crop, expressed at canopy level as specific leaf N ( SLN) or at plant level as N nutrition index ( NNI). To determine the mechanisms through which N affects dry-matter ( DM) production of forage kale, results from two experiments ( N treatment range 0-500 kg ha−1) were analysed for fractional radiation interception ( RI), accumulated radiation ( Racc), RUE, N uptake, critical N concentration ( Nc), NNI and SLN. The measured variables ( DM, RI and SLN) and the calculated variables ( NNI, Racc and RUE) increased with N supply. RUE increased from 0·74 and 0·89 g MJ−1 IPAR for the control treatments to 1·50 and 1·95 g MJ−1 IPAR under adequate N and water in both experiments. This represented an increase in RUE of 52-146% for the range of N treatments used in both experiments, whilst Racc increased by 9-17%, compared with the control treatments. Subsequently, the total DM yield of kale increased from 6·7 and 8 t DM ha−1 for the control treatments to ≥ 19 t DM ha−1 when ≥150 kg N ha−1 was applied. The DM yields for the 500 kg N ha−1 treatments were 25·5 and 27·6 t DM ha−1 for the two experiments. RUE increased linearly with SLN, at an average rate of 0·38 g DM MJ−1 IPAR per each additional 1 g N m−2 leaf until a maximum RUE of 1·90 g MJ−1 IPAR was reached in both experiments. There were no changes in RUE with SLN of > 2·6 g m−2 and NNI >1, implying luxury N uptake. RUE was the most dominant driver of forage kale DM yield increases in response to SLN and NNI. [ABSTRACT FROM AUTHOR]

Winter grazing of forage kale (Brassica oleraceavar.acephalaL.) has been linked to environmental pollution and negative animal health issues. An experiment with seven nitrogen (N) fertiliser application rates (0–500 kg N ha−1) was carried out at Lincoln, Canterbury, New Zealand to investigate N uptake, partitioning, apparent N use efficiency (aNUE) and nutritive value of forage kale. Final harvest dry matter (DM) yield increased four-fold to 25.5 t ha−1when 500 kg N ha−1was applied compared with the 0 kg N ha−1crops, and N uptake by five-fold to 425 kg ha−1. The inability of the crops receiving ≤100 kg N ha−1to attain critical leaf area index and critical level of specific leaf nitrogen content resulted in lower DM yield compared with the higher N fertiliser application rates. The aNUE decreased from 111.6 kg DM kg−1N for the 50 kg N ha−1crops to 37.5 kg DM kg−1N for the 500 kg N ha−1crops. Nitrogen fertiliser application rate had no systematic effect on the crude fibre content of the kale crops. The crude protein content was unaffected by N supply, and ranged between 7.7% and 10.5%. Under conditions of optimal water and nutrient supply on deep soils with high water-holding capacity and long growing season (c. 7 months), it is recommended that N fertiliser is applied at 300 kg N ha−1to achieve a yield of about 22 t ha−1and aNUE of ≥51 kg DM kg−1N applied. [ABSTRACT FROM AUTHOR]

Nitrogen fertilizer is applied to supplement soil nitrogen supply to maximize forage brassica crop dry-matter production. However, nitrogen fertilizer applications in excess of that required to maximize growth result in potentially toxic nitrate-nitrogen ( NO3-N) concentrations in grazeable plant tissues. Three experiments, two for forage kale at Lincoln ( Canterbury) and one for forage rape at Hastings ( Hawke's Bay) in New Zealand were grown under different rates of nitrogen (0-500 kg N ha−1) to determine the effect of different rates of nitrogen on NO3-N content of different plant parts of the crops. One of the kale experiments was grown with either full irrigation or no rain and no irrigation over summer, hereafter referred to as summer drought. The NO3-N concentration on a whole plant (weighted average) basis increased from 0·1 mg g−1 dry matter for the control plots to 2·30 mg g−1 for the 500 kg N ha−1 plots for forage kale. It increased from 0·99 for the control plots to 3·37 mg g−1 for the 200 kg N ha−1 plots for forage rape crops. However, NO3-N concentration increased with N supply under the summer-drought plots from an average of 0·33 mg g−1 when ≤120 kg N ha−1 was applied to 2·30 mg g−1 for the 240 kg N ha−1 treatments but was unaffected by N supply under irrigation. The NO3-N concentrations were higher in the stems and the petiole (which included the midrib of the leaf) than leaves in all three experiments. The NO3-N concentration was highest at the bottom of the kale stem and decreased towards the top. We recommend N application rates based on soil tests results, and for conditions similar to the current studies up to 300 kg N ha−1 under irrigation and adjusted lower N rates for regions prone to dry summers. [ABSTRACT FROM AUTHOR]

Accuracy of determining radiation interception, and hence radiation use efficiency, depends on the method of measuring photosynthetically active radiation intercepted. Methods vary, from expensive instruments such as Sunfleck ceptometers to simple methods such as digital photography. However, before universal use of digital photography there is need to determine its reliability and compare it with conventional, but expensive, methods. In a series of experiments at Lincoln, New Zealand, canopy development for barley, wheat, white clover and four forage brassica species was determined using both digital photographs and Sunfleck ceptometer. Values obtained were used to calculate conversion coefficient (K f/K i) ratios between the two methods. Digital photographs were taken at 45° and 90° for barley, wheat and white clover and at only 90° for brassicas. There was an interaction of effects of crop and cultivar for the cereal crops. Barley closed canopies earlier than wheat, and 'Emir' barley and 'Stettler' wheat had consistently higher canopy cover than 'Golden Promise' and ' HY459′, respectively. Canopy cover was consistently larger at 45° than 90° for cereals. However, for white clover, the angle of digital photography was not important. There was also an interaction between effects of species and method of determining canopy cover for brassicas. Photographs gave higher cover values than ceptometer for forage rape and turnip, but the relationship was variable for forage kale and swede. K f/K i ratios of 1.0-1.10 for cereals, white clover and forage rape and turnip show that digital photographs can be used to estimated radiation interception, in place of Sunfleck ceptometer, for these crops. [ABSTRACT FROM AUTHOR]

Nitrogen (N) supply needs to be closely matched to crop demand to achieve optimum N use efficiency (NUE). Sub-optimal N supply can lead to poor yields, whereas excess N application may cause nitrate leaching and environmental pollution. An experiment with five rates of N: 0, 25, 50, 100 and 200 kg ha−1, was carried out at Lincoln, Canterbury, in New Zealand to define the effects of N supply on growth, N uptake and define how derived NUE may influence nutritive value of fodder beet production. Both dry matter (DM) yield and N uptake increased with N supply, by 39% and 129%, respectively, when 200 kg N ha−1was applied, compared with the control plots. Leaf area index (LAI) also increased with N supply. However, the control crop did not attain critical LAI (LAIcrit) and those receiving 25 and 50 kg N ha−1attained LAIcritfor only a short period of time compared with crops supplied with ≥100 kg N ha−1. This meant that they intercepted less radiation and subsequently had lower DM yield than the high N treatments. The specific leaf nitrogen increased 13% to 2.34 g N m−2leaf when ≥50 kg N ha−1was applied, compared with the control plots. The NUE decreased by 64% from 93 kg DM kg−1N for the 25 kg N ha−1plots compared with the 200 kg N ha−1plots. Nitrogen rate had no effect on the nutritive value of fodder beet. The results suggest 100 kg N ha−1was adequate for optimum DM production and N was important for canopy development and subsequent DM accumulation. [ABSTRACT FROM PUBLISHER]

Establishing the radiation-use efficiency ( RUE) of forage brassica crops will aid our understanding of their photosynthetic performance. The concept of RUE has been developed for cereals and legumes, but there is limited information for forage brassica crops. Three experiments defining the influence of different sowing dates on 'Gruner' kale ( Brassica oleracea acephala L.) dry matter production were conducted at Hastings (Hawkes Bay) and Lincoln (Canterbury) in New Zealand between 2002 and 2009. These trials were also evaluated for radiation interception and RUE. Delayed sowing increased RUE in two out of three experiments across sites: from 1·93 g MJ−1 photosynthetically active radiation ( PAR) for December-sown crops to 2·72 g MJ−1 PAR ( P < 0·001) for January-sown crops at Hastings and from 1·50 for September-sown crops to 2·00 g MJ−1 PAR ( P < 0·001) for November-sown crops at Lincoln. The different sowing dates and years of experimentation provided a range of mean temperatures (from 13 to 16°C) during the vegetative period. Across years and sowing dates, RUE was strongly correlated with mean temperature (R2 = 0·81) and sowing date (R2 = 0·64), but weakly correlated with season length (R2 = 0·11) and dry matter (R2 = 0·002). There was also a strong correlation (R2 = 0·83) between sowing date and mean temperature. The increase in RUE with delayed sowing was therefore mainly attributed to increased mean temperatures. Radiation-use efficiency increased at about 0·41 g MJ−1 for each 1°C increase from 13 to 16°C. [ABSTRACT FROM AUTHOR]

Previous research has shown that the application of fertilizer nitrogen (N) can lead to an accumulation of nitrate nitrogen (NO3-N) in forage brassicas, particularly when N application rates exceed that required to obtain maximum crop yield. However, there are no data examining the effect of timing of fertilizer application on NO3-N accumulation. An experiment was established in 2009 with four forage brassica crops (turnips, rape, kale and swedes) and three N fertilizer treatments (early N, late N and double N) at Lincoln, Canterbury, New Zealand. The N treatments, which differed among crops depending on crop duration, consisted of rates and timings of N fertilizer. For the turnips and rape, the early N treatment consisted of 200 kg N/ha applied 16 days after sowing; the late N treatment consisted of 200 kg N/ha applied 40 days after sowing; and the double N treatment consisted of 200 kg N/ha applied 16 days after sowing and a further 200 kg N/ha applied 40 days after sowing. For the kale and swedes, the early N treatment consisted of 400 kg N/ha applied 16 days after sowing; the late N treatment consisted of 400 kg N/ha applied 72 days after sowing; and the double N treatment consisted of 400 kg N/ha applied 16 days after sowing and a further 400 kg N/ha applied 72 days after sowing. There were differences in yield between species that reflected their growth duration but no yield differences between N treatments. Averaged across all species, plant NO3-N content was greater in crops that received the double rate of N than either the early or late N treatments. Importantly, the late N treatment (3.7 mg/g) accumulated almost double (P < 0.001) the plant NO3-N content of the early N treatment (2.0 mg/g). Averaged across all N treatments, the leafy crops (rape and kale) (5.5 mg/g) had nearly double (P < 0.001) the NO3-N content of the bulb crops (turnip and swedes) (2.9 mg/g). In general, the stems had the highest NO3-N content across all crops, followed by the bulbs. Leaves had the lowest NO3-N content. Overall, these results indicate that early application of fertilizer N could be used to minimize NO3-N accumulation in forage brassicas. [ABSTRACT FROM PUBLISHER]

Defining the critical nitrogen concentration (Nc; g N kg−1) for maximum growth of forage brassicas will aid in the fertilizer management of these crops. Typically, the Nc value decreases with increasing crop biomass. In this paper, we used a nitrogen (N) response experiment with kale ( Brassica oleracea) to define a critical N dilution (Nc = 55·3 × biomass−0·47). However, at biomass <3·4 t ha−1, a constant NC of 31·2 g N kg−1 was found. This N dilution curve compared favourably with published data sets for a range of forage brassicas but was substantially different from the established N dilution curve for oilseed rape ( Brassica napus). This study also found a strong relationship ( R2 = 0·81) between the nitrogen nutrition index (NNI) and the NO3 content of forage brassicas from a range of data sets. The NNI is the actual N concentration of the shoot as a ratio of the Nc from the established curve. The relationship between NNI and NO3 contents was significantly different between leafy forage brassica crops and root forage brassicas. For each 0·1 increase in NNI, the proportion of total N that was in the form of NO3 increased by 2·7% for leaf/stem brassicas and 0·60% for root crop brassicas. The critical dilution curve defined in this study can be used to manage fertilizer N in forage brassica crops, so that growth can be maximized but the risk of high NO3 concentrations in the forage can be minimized. [ABSTRACT FROM AUTHOR]

The growing importance of fodder beet ( Beta vulgaris subsp. vulgaris var. alba L.) as stock feed in recent years has created the need to develop a crop model to help assess crop yield potential across environmental growth conditions. This paper describes the development of a biophysical model for simulating fodder beet growth and development. The model was developed using the Plant Modelling Framework (PMF) within the next generation Agricultural Production Systems sIMulator (PMF-APSIM). The model was parameterised/calibrated and validated using independent datasets from field experiments conducted in the Canterbury region of New Zealand. A sensitivity analysis was conducted to explore yield response to variation in the extinction coefficient and the air temperature. The results show that canopy-related variables (leaf appearance, leaf senescence, leaf area index and light interception) were the most accurately simulated. Dynamic dry matter (DM) and nitrogen (N) accumulation in different plant organs were simulated with intermediary accuracy. Reduced accuracy was mainly observed in the earliest (September) and latest (December) sowing dates. This suggests that responses to seasonal environmental drivers, such as day length and threshold temperatures, are areas that require further research. Similarly, more mechanistic representations of carbon and N partitioning to different plant organs may improve simulation accuracy. The sensitivity analysis showed that DM production was responsive to temperature and the extinction coefficient. This initial development and testing of the fodder beet model in APSIM has helped to identify key knowledge gaps in the understanding of the physiology of the crop and provides new directions for model development. [ABSTRACT FROM AUTHOR]