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The impact of chemical to organic fertilizer substitution on soil labile organic and stabilized N pools under intensive farming systems is unclear. Therefore, we analyzed the distribution of soil total N (STN), particulate organic N (PON), microbial biomass N (MBN), dissolved organic N (DON), and mineral N (NO3− and NH4+) levels down to 100 cm profile under wheat–maize rotation system in northern China. The experiment was established with four 270 kg ha−1 N equivalent fertilizer treatments: Organic manure (OM); Organic manure with nitrogen fertilizer (OM + NF); Nitrogen fertilizer (NF); and Control (CK). Results found that the OM and OM + NF treatments had significantly higher STN, PON, MBN, DON, and NO3− contents in 0–20 cm topsoil depths. Conversely, the NF treatment resulted in the highest (p < 0.01) DON and NO3− depositions in 40–100 cm subsoil depths. The NH4+ contents in selected profile depths were significantly highest (p < 0.01) under OM treatment. The correlations between STN and its fractions were positively significant at 0–10 and 10–20 cm topsoil depths. Our results suggest that partial substitution of chemical fertilizer with organic manure could be a sustainable option for soil N management of intensive farming systems.

Plastic mulching (PM) has become an important agricultural practice to improve crop yields worldwide, while there is still a lack of methods to quantify the complex spatial variations of soil water content (SWC) in the PM field. In this study, a methodology for using Electrical Resistivity Tomography (ERT) to get SWC information in the PM field was presented. Its performance in monitoring SWC was validated, and the spatial variation of SWC was analyzed using the ERT results. A simplified Waxman and Smits model was selected to calibrate the pedo-physical relationship, and it showed good performance (coefficient of determination > 0.92). With the calibrated model, the SWC obtained using ERT showed good agreement with soil moisture sensors in different soil layers (RMSE

Ripening of fleshy fruits involves complex physiological, biochemical, and molecular processes that coincide with various changes of the fruit, including texture, color, flavor, and aroma. The processes of ripening are controlled by ethylene in climacteric fruits and abscisic acid (ABA) in non-climacteric fruits. Increasing evidence is also uncovering an essential role for polyamines (PAs) in fruit ripening, especially in climacteric fruits. However, until recently breakthroughs have been made in understanding PA roles in the ripening of non-climacteric fruits. In this review, we compare the mechanisms underlying PA biosynthesis, metabolism, and action during ripening in climacteric and non-climacteric fruits at the physiological and molecular levels. The PA putrescine (Put) has a role opposite to that of spermidine/spermine (Spd/Spm) in cellular metabolism. Arginine decarboxylase (ADC) is crucial to Put biosynthesis in both climacteric and non-climacteric fruits. S-adenosylmethionine decarboxylase (SAMDC) catalyzes the conversion of Put to Spd/Spm, which marks a metabolic transition that is concomitant with the onset of fruit ripening, induced by Spd in climacteric fruits and by Spm in non-climacteric fruits. Once PA catabolism is activated by polyamine oxidase (PAO), fruit ripening and senescence are facilitated by the coordination of mechanisms that involve PAs, hydrogen peroxide (H2O2), ABA, ethylene, nitric oxide (NO), and calcium ions (Ca2+). Notably, a signal derived from PAO5-mediated PA metabolism has recently been identified in strawberry, a model system for non-climacteric fruits, providing a deeper understanding of the regulatory roles played by PAs in fleshy fruit ripening.

Climate change impacts crop productivity as atmospheric conditions and water supply change, particularly in intensive cropping areas. This study used the validated AquaCrop Model, which was run with downscaled daily climate data produced by SDSM and CanESM2. The changes in the potential grain yield of winter wheat and summer maize and water budget during the cropping seasons were estimated for the Huang-Huai-Hai Plain (3H Plain) under RCP4.5 and RCP8.5 scenarios. The results show that the potential yield of winter wheat is increasing with similar spatial patterns in the 2030s, 2050s, and 2080s, with much of the increase is distributed in Shandong and northeastern parts of Henan. During the winter wheat growth period, the water budget deficit will likely improve from −210 mm in the 2030s to −202 mm in 2080s under RCP4.5 and from −206 mm in the 2030s to −191 mm in 2080s under RCP8.5 across the 3H Plain. The water budget during the winter wheat period will continue to be in deficit in the north 3H Plain and improvements are estimated mostly in the lower southern areas of the Plain. The summer maize potential yield is estimated to increase from the baseline period, but yields will decrease by 0.81%, 1.19%, and 2.10% in the 2030s, 2050s, and 2080s, respectively, under RCP8.5 compared to RCP4.5. During the summer maize growth period, the water budget is also estimated to improve from 109 mm in 2030s to 126 mm in 2080s under RCP4.5 and 107 mm in the 2030s to 163 mm in 2080s under RCP8.5. This increase is mainly estimated in the central and south of the 3H Plain. The estimated ETc of winter wheat shows no significant decrease, while the reduction of 6 mm and 13 mm for summer maize is observed under RCP4.5 and RCP8.5, respectively. The study provides scientific evidence to devise adaptation and mitigation climate change strategies for agricultural productivity and water resource management.

Fertigation can improve water use efficiency (WUE) compared with conventional separate supply of water and fertilizers to plants. Yet the mechanisms underlying the improved WUE under fertigation remain largely elusive. Therefore, the impact of water and nitrogen (N) on leaf gas exchange, plant water relations, ABA signaling and WUE as well as leaf δ13C and δ18O were investigated in order to unravel how water and N modulate plant WUE. Results showed that reduced soil water regimes under N fertigation caused partial closure of stomata via decreased plant water status and intensified root-to-shoot ABA signaling, resulting in improved intrinsic WUE (WUEi). Decreased soil water regimes increased plant WUE (WUEp) and leaf δ13C, and the increased leaf δ13C was due to reduced gs and/or higher specific leaf N content enhanced photosynthetic capacity. Leaf δ18O and δ13C further indicated that the significant increase in leaf δ13C under the reduced water regimes was caused primarily by reductions in gs compared with N nutrition. Therefore, gs rather than N nutrition predominated regulation of plant WUE under fertigation. Moderate soil water regimes with sufficient N supply are recommended for fertigation in terms of achieving high fresh fruit yield, WUE and nutrient uptake.

Understanding land–atmosphere interactions in rainfed spring maize fields is important for elucidating land surface processes on the Loess Plateau. In this study, water vapor and energy flux observations were used to investigate the evapotranspiration (ET) partitioning and energy budget in a rainfed spring maize field on the Loess Plateau in 2015 and 2016. Over this 2-year period, the total ET was 851 mm, slightly higher than the total precipitation (847 mm). Plant transpiration (T) accounted for 59% and 56% of ET during the 2015 and 2016 growing seasons, respectively. The most important factor controlling daily ET and soil evaporation was net radiation (Rn), and the most important factor controlling daily T was the green leaf area index (GLAI) during the growing season; Rn also controlled ET during the non-growing season. Downward longwave radiation offset 83% of upward longwave radiation in both years; 19% and 18% of downward shortwave radiation was reflected back to the atmosphere by the land surface in 2015 and 2016, respectively. During the growing season, latent heat flux was the largest consumer of Rn; during the non-growing season, sensible heat flux was the dominant consumer of Rn. Soil heat flux (G) and imbalance energy (Imb) did not exhibit obvious seasonal variation pattern, and G/Rn and Imb/Rn values were relatively low during different periods. Midday evaporative fraction (EF), daily crop coefficient (Kc), midday Priestley–Taylor coefficient (α), and midday surface conductance (gs) increased linearly with increasing GLAI, and the midday Bowen ratio (β) decreased linearly with increasing GLAI during the growing season. Midday EF, daily Kc, and midday α increased exponentially with increasing midday gs, and midday β decreased exponentially with increasing midday gs during the growing season and the non-growing season; the threshold value of midday gs was approximately 8 mm s−1 in the spring maize field.

Polyamines (PAs) participate in many plant growth and developmental processes, including fruit ripening. However, it is not clear whether PAs play a role in the ripening of strawberry (Fragaria ananassa), a model nonclimacteric plant. Here, we found that the content of the PA spermine (Spm) increased more sharply after the onset of fruit coloration than did that of the PAs putrescine (Put) or spermidine (Spd). Spm dominance in ripe fruit resulted from abundant transcripts of a strawberry S-adenosyl-l-Met decarboxylase gene (FaSAMDC), which encodes an enzyme that generates a residue needed for PA biosynthesis. Exogenous Spm and Spd promoted fruit coloration, while exogenous Put and a SAMDC inhibitor inhibited coloration. Based on transcriptome data, up- and down-regulation of FaSAMDC expression promoted and inhibited ripening, respectively, which coincided with changes in several physiological parameters and their corresponding gene transcripts, including firmness, anthocyanin content, sugar content, polyamine content, auxin (indole-3-acetic acid [IAA]) content, abscisic acid (ABA) content, and ethylene emission. Using isothermal titration calorimetry, we found that FaSAMDC also had a high enzymatic activity with a Kd of 1.7 × 10-3 m In conclusion, PAs, especially Spm, regulate strawberry fruit ripening in an ABA-dominated, IAA-participating, and ethylene-coordinated manner, and FaSAMDC plays an important role in ripening.

Numerical solution of the Richards equation with Hydrus-2D model is a low cost and fast way to get information on spatio-temporal soil water dynamics. Previous researches with Hydrus-2D have developed two different approaches to represent the rainfall infiltration in irrigated field with plastic mulching: ‘BP’ – an approach comprised by bare strip boundary and plastic strip boundary without consideration of film side infiltration;‘BP + ’- an approach comprised by bare strip and plastic strip with integrating the process of film side infiltration by increasing the rainfall infiltration amount in bare strip. Nevertheless, the performance of these approaches has not yet been evaluated in rain-fed fields. Considering much more dominant role of rainfall infiltration in rain-fed agriculture, we tested an additional approach which comprised a bare strip, plastic strip and planting hole (BPH) to take into account the effect of the rainfall canopy redistribution and film side infiltration, and we compared its performance to the two existing approaches. Results suggested BP completely failed to reproduce the soil water content (SWC) in all soil layers of plastic strip and in the deep soil layers of bare strip. BP+ overestimated the SWC in 0–20 cm of the bare strip, while the performance of BPH was acceptable in different positions. After that, we compared the soil water distribution between no-mulched field (NM) and plastic mulched field (PM) with approach BPH. Our simulation showed that the highest SWC in PM occurred near the planting hole, SWC in the center zone of plastic strip was lower, while SWC in the bare strip was lowest. PM improves the soil water availability not only in the plastic strip but also in the bare strip as compared to NM.

Based on the standardized Euclidean distance method, an evaluation theory for sustainable agricultural development was constructed, which includes a sustainable agricultural development model, an evaluation function model, a sustainable agricultural development exponent (SADE), a rank of the sustainable agricultural development, an index frame of the sustainable agricultural development, a goal system, and a zero system. Data from Zhenyuan County of Gansu province (ZYC) between 2000 and 2012 was used as a case study of the theory. The SADE of ZYC was [0.34, 0.90], and the agriculture system exhibited low sustainability from 2000 to 2003, mid sustainability from 2004 to 2007, and high sustainability from 2008 to 2012. The results explained the actual ZYC situation, and showed that the Euclidean distance method of sustainable agricultural development is feasible. The innovativeness and merits of the method include: (1) reliable methodology, (2) construction using goal and zero systems, which serve as reference systems of sustainable agricultural development and allow control of the evaluation, and (3) index weights embedded in the evaluation function, which prevents errors or mistakes in the expert scoring method and prevents the reassignment of index weights due to adding or subtracting indicators. The main reasons that the SADE increased in ZYC include suitable chemical fertilization and pesticide application, enhancement of conservation farming areas, soil testing and fertilizer-formulated areas, and drinking water security in rural and non-disaster crop areas. The main problems with increasing the SADE in ZYC include straw application and low farmer income, both of which should be increased.

We estimated ecosystem respiration (Re) and its components in a rainfed spring maize field in the Loess Plateau, China, during the growing seasons of 2012, 2013, and 2014 using measurements of eddy covariance and soil respiration (Rs). The multi-factor equation, which included photosynthetic active radiation, 5-cm soil temperature, 10-cm soil water content, and green leaf area index (GLAI), had goodness-of-fit values of between 0.81 and 0.94 for Re, autotrophic respiration (Ra), and above-ground autotrophic respiration (Raa), and goodness-of-fit values of between 0.50 and 0.67 for Rs, below-ground autotrophic respiration (Rab), and heterotrophic respiration (Rh). The highly significant linear correlations between gross primary production (GPP) and Re and its components indicate that GPP had a strong influence on Re and its components. The growing season Re was dominated by Ra (64–71%), which in turn was dominated by Raa (63–73%). Although Rs was mainly made up of Rh (56–61%), Rs resembled Rab more closely than Rh. The relationships between GLAI and Ra/Re and between GLAI and Rab/Rs were described by logarithmic equations with goodness-of-fit values of between 0.88 and 0.89 and between 0.77 and 0.84, respectively, indicating that GLAI controlled Ra/Re and Rab/Rs.

Crop simulation models play an essential role in evaluating irrigation management strategies for improving agricultural water use in crop production. In this study, the AquaCrop model was used to calibrate and validate the grain yield and biomass of 11 cultivars (9 winter wheat and 2 summer maize) under full and water-saving irrigation practices. The model results were verified with the available data from the published literature. Under the full irrigation practice, widely used by farmers in the region for winter wheat, the Normalized Root Mean Square Error (NRMSE) was found to be between 2.00–9.90% for grain yield, 2.40–10.85% for biomass, and 0.42–19.61% for water productivity. Under water-saving irrigation for winter wheat, the NRMSE range was found to be between 5.80–16.00% for grain yield, 3.70–17.30% for biomass, and 3.80–13.79% for water productivity. For summer maize, the NRMSE was 5.95%, 6.08%, and 16.41% under full irrigation, and 9.51%, 8.41%, and 3.60% under water-saving irrigation for grain yield, biomass, and water productivity, respectively. For winter wheat and summer maize, the simulation accuracy of grain yield was high under full irrigation, with percent deviations under ± 11.00%. In this study, the simulation accuracy for winter wheat was low under water-saving irrigation, while the model simulated the yield and biomass for summer maize to acceptable accuracy. The model can be reliably used as a tool to simulate grain yield and biomass across the NCP region for winter wheat and summer maize. However, the limitations of the model must be considered when simulating winter wheat under water-stressed conditions.

Increasing attention has been paid to the potential of croplands to mitigate rising atmospheric CO 2 concentrations by adopting appropriate cultivation practices. Plastic film mulching with straw returning to promote crop yields is widely used in rainfed agriculture; however, information about the effect of this practice on carbon exchange is limited. Eddy covariance measurements were used to investigate carbon fluxes in a rainfed spring maize cropland under plastic film mulching with straw returning on the Chinese Loess Plateau in 2013 and 2014. Carbon fluxes showed a clear seasonal variation, with the green leaf area index (GLAI) being the dominant control factor. The diurnal and seasonal ecosystem respiration (R e ) values were driven by gross primary productivity (GPP), and the daily R e per unit daily GPP increased by 0.32 g C m − 2 d − 1 . The ecosystem apparent quantum yield (α), ecosystem maximum photosynthetic capacity (P max ), and ecosystem respiration rate at 10 °C (R 10 ) also showed clear seasonal variations, and the mean monthly α, P max , and R 10 per unit mean monthly GLAI increased by 1.44 × 10 − 2 μmol CO 2 μmol PAR − 1 , 1.12 mg CO 2 m − 2 s − 1 , and 2.08 × 10 − 2 mg CO 2 m − 2 s − 1 respectively. The temperature sensitivity of ecosystem respiration was insensitive to GLAI, and ranged from 1.58 to 2.85, with the maximum value appearing in the non-growth seasons. Annual GPP values were 1547 and 1370 g C m − 2 in 2013 and 2014, respectively, approximately 60% of which was lost through R e , which resulted in annual net CO 2 uptakes of 618 and 540 g C m − 2 in 2013 and 2014 respectively. Compared to the non-mulching spring maize field with straw returning, the spring maize field under plastic film mulching with straw returning was a stronger carbon sink (76 and 41 g C m − 2 in 2013 and 2014, respectively). Plastic film mulching with straw returning is recommended as an effective approach to sequester carbon in rainfed spring maize cropland on the Loess Plateau and to mitigate greenhouse effects.

‘One film for 2 years’ (PM2) has been proposed as a practice to control the residual film pollution; however, its effects on grain-yield, water-use-efficiency and cost-benefit balance in dryland sp...

Energy and water exchange processes between the land surface and atmosphere drive photosynthesis, evapotranspiration, sensible heat flux, energy storage in vegetation, and heating of the soil. Thus, understanding of energy exchange and partitioning is of importance for crop model development and water use efficiency improvement in raifed agro-ecosystems. The present study investigated the energy exchange and partitioning over rainfed maize croplands under two cultivation methods—conventional flat planting without mulching (CK) and a furrow-ridge system with plastic film partially mulching (MFR) for two growing seasons through synchronous measurements of eddy covariance system with multi micro-lysimeters on the eastern Loess Plateau of China, the effects of rainfall on the energy partitioning were also discussed. The results indicated that average energy balance closure were 0.89 and 0.84 for CK and MFR at half-hourly, 0.91 and 0.93 at daily interval, respectively. Each energy flux component presented typical diurnal variations during the entire growing stage, which was a single-peak curve. Latent heat flux (LE) showed typical seasonal variation that it increased during May to June, and reach a high value in July, then decreased gradually. However, compared to LE, sensible heat flux (H) and Bowen ratio showed a similar opposite trends, LE became the main consumer of available energy after maize plants grown quickly. LE of spring maize was the main component of net radiation (R n ), followed by H and soil heat flux (G), which accounted for 64.3%, 28.6%, and −0.2% for CK and 68.5%, 29.7%, and 0.1% for MFR in 2011, 56.8%, 20.1%, and 2.8% for CK and 58.0%, 25.5%, and 8.6% for MFR in 2012, respectively. Transpiration was the main component of LE, which accounted for 54.3%–76.6% of LE for the both treatments. Compared to the energy fluxes before rainfall, LE increased significantly while H and G decreased after rainfall in development stage, however in late stage, the changes in soil water content resulted by rainfall didn’t increase LE significantly for the both treatments due to the high canopy cover and senescent maize plants.

Assessing the carbon budget of rainfed agricultural ecosystems is a vital component in the process of estimating the global carbon balance. We used eddy covariance techniques combined with soil respiration measurements to estimate the carbon budget of a rainfed spring maize field where straw returning was practiced, on the Loess Plateau, China, during 2012-2014. Carbon fluxes and their components (except heterotrophic respiration, Rh) exhibited single-peak seasonal patterns, and linear relationships were found between daily gross primary productivity (GPP) and net ecosystem exchange (NEE), and between daily GPP and ecosystem respiration (Re), with goodness of fit value of 0.96 and 0.85, respectively. The green leaf area index was the most important factor controlling seasonal variations in daily NEE, Re, and GPP during the growing season, followed by photosynthetically active radiation and air temperature (Ta). Daily Re was mainly controlled by air temperature during the non-growing season, when Re accounted for only ~17% of the annual Re due to winter temperatures. Growing season plant respiration (Rp) was the most important source of carbon emissions from the maize field, with aboveground plant respiration being the major part of Rp. Rh accounted for ~60% of total soil respiration. Only ~60% of the annual GPP was lost as Re, resulting in an average annual net CO2 uptake of 509gCm-2. Taking into account carbon exported (483gCm-2) and carbon imported (10gCm-2), the average annual net biome productivity was 37gCm-2, indicating that the spring maize field with straw returning on the Loess Plateau was a weak carbon sink.

The ratio of evaporation to evapotranspiration (E/ET) and crop coefficients (Kc) are important parameters for evaluating the water-saving potentials of agronomic technologies and they may vary with different practices of dryland cultivation. This study synchronously investigated changes of E/ET and Kc for three years using two eddy covariance systems and multi-microlysimeters under two cultivation methods—conventional flat planting without mulching (CK) and a furrow-ridge system with plastic film partially mulching (MFR)—on the semiarid Loess Plateau of China. Due to an increase of vapor diffusion resistance at the soil-air interface partially mulched by plastic film, the average E and ET of MFR were lower than those of CK by 38.1% and 9.3%, respectively, for the three growing seasons. Thus, the average E/ET in MFR decreased by 11.2 percentage points compared with CK. E/ET showed a significant logistic function with the green leaf area index (GLAI) under both treatments during the three growing seasons. The seasonal Kc varied with GLAI following a step function curve for both treatments, and was linearly correlated to GLAI with significance levels when GLAI was below the thresholds of 3.0 and 3.2–3.4 for CK and MFR, respectively. Maximum Kc values were 1.01 ± 0.05 and 0.91 ± 0.09 for CK and MFR, respectively, at the middle crop growth stage. These results suggest that MFR can significantly reduce E/ET and maximum Kc, which help to improve yield and water use efficiency in rainfed spring maize fields. Consequently, MFR enhanced the average grain yield and crop water use efficiency by 12.5% and 24.6%, which amounted to 11527 kg/ha and 3.36 kg/m3, respectively. Therefore, MFR promoted crop water productivity and is an effective approach to solve water crises in dryland regions.

Multi-level crop water use efficiency, i.e. ratio of productivity to water use at canopy, ecosystem, biomass, grain yield and net biome production (NBP) levels, is essential for evaluating water productivity and footprints of agronomy technologies and may vary with different methods of dryland tillage. This study investigated their changes under two tillage methods: conventional flat tillage without mulching (CK) and plastic film partially mulched furrow-ridge (MFR) for three years through synchronous measurements of two eddy covariance systems with multi micro-lysimeters on the eastern Loess Plateau of China. Water flux linearly correlated to canopy assimilated CO 2 and net ecosystem CO 2 exchange at half-hourly and daily scales, and also to biomass increments at seasonal scale with significant levels for both treatments for all three years. At canopy level, the slopes for these correlations in MFR were very close to those of CK for three years. However, the absolute slopes for these correlations in MFR were always higher than those of CK at ecosystem and biomass levels. Seasonal water use efficiency significantly changed with green leaf area index (GLAI) at ecosystem but not canopy and biomass levels. During three whole growing seasons, average water use efficiency in MFR were higher by 24.4%, 36.7%, 29.3% and 25.7% than those of CK at ecosystem, biomass, grain and net biome production levels, respectively. These results demonstrated that MFR can significantly enhance water use efficiency at ecosystem, biomass, grain and NBP levels except for canopy level, which should help sustainable crop production with minimum water footprints in water-limited environment.

Drought is an important abiotic stress that seriously restricts crop productivity. An understanding of drought tolerance mechanisms offers guidance for cultivar improvement. In order to understand how a well-known wheat genotype Jinmai 47 responds to drought, we adopted the iTRAQ and LC/MS approaches and conducted proteomics analysis of leaves after exposure to 20% of polyethylene glycol-6000 (PEG)-induced stress for 4 days. The study identified 176 differentially expressed proteins (DEPs), with 65 (36.5%) of them being up-regulated, and 111 (63.5%) down-regulated. DEPs, located in cellular membranes and cytosol mainly, were involved in stress and redox regulation (51), carbohydrate and energy metabolism (36), amino acid metabolism (24), and biosynthesis of other secondary metabolites (20) primarily. Under drought stress, TCA cycle related proteins were up-regulated. Antioxidant system, signaling system, and nucleic acid metabolism etc. were relatively weakened. In comparison, the metabolism pathways that function in plasma dehydration protection and protein structure protection were strongly enhanced, as indicated by the improved biosynthesis of 2 osmolytes, sucrose and Proline, and strongly up-regulated protective proteins, LEA proteins and chaperones. SUS4, P5CSs, OAT, Rab protein, and Lea14-A were considered to be important candidate proteins, which deserve to be further investigated.

Twelve winter wheat (Triticum aestivum) genotypes were examined for differences in grain yield, water use efficiency (WUE), and stable carbon isotope composition (δ13C) in flag leaves. The plants were subjected to rain-fed treatment and supplemental irrigation at the jointing and anthesis stages, during the 2015–2016 and 2016–2017 winter wheat growing seasons. The relationships between δ13C with grain yield and WUE were analyzed under two different water environments. The results indicated that there were significant differences in δ13C, grain yield, and WUE among wheat genotypes both under rain-fed and supplemental irrigation conditions. The δ13C values increased with grain-filling proceeding, the δ13C being lower under supplemental irrigation treatment than that under rain-fed treatment. The relationships between the average of δ13C with grain yield and WUE were significantly positive during three measurement periods (R2 = 0.5785 − 0.8258), whether under rain-fed or irrigation environments. This suggests that δ13C might be associated with the grain yield and WUE in winter wheat under rain-fed and supplemental irrigation conditions in the climate region of the northwest Huang-Huai-Hai Plain of China.

Fertigated areas of wheat and maize in the North China Plain (NCP) have grown rapidly during recent years, but little information is available on the effects of different nitrogen (N) fertilizers applied through drip fertigation on wheat and maize. A field experiment was conducted in the NCP during 2012−2016 to evaluate the effects of urea, ammonium nitrate, ammonium sulfate and calcium nitrate applied by drip fertigation (no N as the control, CK) on grain yield, water use efficiency (WUE), N use efficiency (NUE) and N loss in wheat and maize. A total of 250 kg N ha−1 and 205.5 kg N ha−1 were split into six and four applications and applied by drip fertigation at key growth stages during the wheat and maize growing seasons, respectively. The results showed that urea and calcium nitrate produced higher yields (p

Accurately estimating crop evapotranspiration ( ET ) is essential for agricultural water management in arid and semiarid croplands. This study developed extreme learning machine (ELM) and generalized regression neural network (GRNN) models for maize ET estimation on the China Loess Plateau. Maize ET , meteorological variables, leaf area index ( LAI ), and plant height ( h c ) were continuously measured during maize growing seasons of 2011–2013. The meteorological data and crop data including LAI and h c from 2011 to 2012 were used to train the ELM and GRNN using two different input combinations. The performances of ELM and GRNN were compared with the modified dual crop coefficient ( K c ) approach in 2013. Results indicated that ELM1 and GRNN1 using meteorological and crop data as inputs estimated maize ET accurately, with root mean square error (RMSE) of 0.221 mm/d, mean absolute error (MAE) of 0.203 mm/d, and NS of 0.981 for ELM1, RMSE of 0.225 mm/d, MAE of 0.211 mm/d, and NS of 0.981 for GRNN1, respectively, which confirmed better performances than the modified dual K c model. Performances of ELM2 and GRNN2 using only meteorological data as input were poorer than those of ELM1, GRNN1, and modified dual K c approach, but its estimation of maize ET was acceptable when only meteorological data were available.