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BACKGROUND Limited and erratic precipitation with inefficient irrigation scheduling often leads to an unstable crop yield and low water-use efficiency (WUE) in semi-arid and semi-humid regions. A 2-year field experiment was conducted to evaluate the effect of three irrigation strategies (conventional irrigation (CK), full-drip irrigation (FI), based on crop evapotranspiration and precipitation forecast, and deficit drip irrigation (DI) (75% FI)) on photosynthetic characteristics, leaf-to-air temperature difference (∆T), grain yield, and the WUE of summer maize. RESULTS The results showed that the daily average net photosynthetic rate (Pn) of DI and FI increased by 25.4% and 25.8% at jointing stage in 2018, and 26.3% and 26.5% at grain-filling stage in 2019 compared with CK, respectively. At jointing stage in 2018 and grain-filling stage in 2019, the transpiration rate (Tr) of DI was significantly lower than that of FI (P 0.05). The ∆T between 12:00-14:00 of DI and FI was significantly lower than that of CK at jointing stage in 2018 and grain-filling stage in 2019 (P

A field experiment was carried out to investigate effect of nitrogen (N) supply method on root growth and its correlation with the above-ground parts in maize (Zea mays L.) under alternate partial root-zone irrigation (APRI) at Wuwei, northwest China in 2012 and 2014. The treatments included alternate N supply, conventional N supply and fixed N supply under APRI (designated AN, CN and FN, respectively), with an additional CN fertilizer treatment coupled with conventional irrigation (CK). Ridges were built in a west-east direction. Root weight density (RWD) in the 0–100 cm soil layer and shoot biomass at the V6, V12, VT, R2 and R6 stages, and grain yield and yield components at the R6 were determined. Results showed that RWD around the plant (i.e. under the plant, south and north of the plant) in the 0–40 cm soil layer varied among different treatments at the VT, R2 and R6 stages. The RWD north and south the plant were comparable during maize growth stages for AN, CN and CK, while FN significantly decreased the RWD of its no N supply side at the three stages and markedly decreased the RWD of its N supply side at the VT. AN and CN significantly increased the RWD, shoot biomass at the three stages, and grain yield compared with FN and CK. Grain yield was positively correlated with RWD in the 0–40 cm soil layer at the three stages. These results suggested that AN and CN produced a relatively uniform distribution of roots and a greater root biomass, which contributed to the enhanced shoot biomass and grain yield of maize under APRI.

Mango (Mangifera indica L.) is one of the widely grown fruit crops and brings remarkable economic benefit in the xerothermic regions of southwest China. However, mango yield and quality can not be guaranteed due to the severe seasonal drought, low precipitation and extensive management of water and fertilizer. To investigate the effects of irrigation amount and fertilizer regime on mango yield, fruit quality, water use efficiency (WUE) and partial fertilizer productivity (PFP), an orthogonal experiment [L9(3)4] was conducted on mango under drip fertigation during 2018–2019. The four factors were irrigation amount (IA) and fertilization rate at the flowering (FⅠ), fruit expansion (FⅡ) and fruit ripening (FⅢ) growth stages. There were three irrigation amounts, i.e., full irrigation (FI: 100%ETc), mild deficit irrigation (DIM: 75%ETc) and severe deficit irrigation (DIS: 50%ETc), and three fertilization rates, i.e., 75 (F75), 50 (F50) and 25 (F25) kg ha−1 using a compound water-soluble fertilizer (N:P2O5:K2O=20%:20%:20%). The results showed the order of factors influencing fruit yield and WUE in terms of their importance was IA, FⅡ, FⅠ and FⅢ, that influencing water, vitamin C and carotenoid contents in fruit was IA, FⅢ, FⅡ and FⅠ, and that influencing soluble solids and total sugar contents was IA, FⅢ, FⅠ and FⅡ. The WUE of DIMFⅠ50FⅡ75FⅢ25 was highest. FIFⅠ25FⅡ75FⅢ50 achieved the highest fruit yield, PFP and contents of soluble solid, vitamin C and carotenoid. DIMFⅠ25FⅡ50FⅢ75 had the highest total sugar content and the lowest titratable acid content. Based on the comprehensive scoring method, DIMFⅠ50FⅡ75FⅢ25 achieved the optimum score in terms of fruit yield and water–fertilizer use efficiency, while FIFⅠ25FⅡ75FⅢ50 was optimum for fruit quality. Further, the TOPSIS method indicated DIMFⅠ50FⅡ75FⅢ25 had the optimal comprehensive benefit. To obtain high yield, quality and water–fertilizer use efficiency, the recommended water and fertilizer scheduling was irrigation with 75% ETc and fertilization with 50, 75 and 25 kg ha−1 at the flowering, fruit expansion and fruit ripening stages, respectively. The research results provided a scientific reference for identified optimum combination irrigation and fertilizer in the xerothermic environment of southwest China.

The winter wheat-summer maize rotation system is one of the most successful intensification agricultural systems in China, but low and unstable grain yield (GY) and high soil nitrate-N leaching caused by erratic precipitation and inefficient management of irrigation and fertilization have attracted wide attention. A two-year (2018–2020) field experiment was carried out to evaluate the effects of four water and nitrogen management strategies (a conventional irrigation and fertilization (CK) and three drip fertigation treatments (rain-fed: RF, deficit irrigation: DI and full irrigation: FI)) on soil water, soil nitrate-N residual, GY, water productivity (WP), nitrogen use efficiency (NUE) and net income in a winter wheat-summer maize rotation system. The results indicated that water and nitrogen management strategies had significant effects on soil water content in the 0–320 cm soil profile. More than 90 mm soil water in the 0–320 cm soil layer was consumed by winter wheat, and the soil water consumption followed the order of RF > DI > CK > FI. The soil water consumption can be replenished by irrigation and precipitation during the summer maize season, but the soil water in 180–260 cm under RF was significantly lower than that in the other treatments, which could not be fully replenished. There was no significant difference in the nitrate-N residual in the 0–180 cm soil layer among the treatments at harvest, but the nitrate-N residual rate of CK (less than 40% and 30% at winter wheat and summer maize harvest) was significantly lower than that of drip fertigation (more than 50% and 40% at winter wheat and summer maize harvest) in the 0–60 cm soil profile, but significantly higher than that in the 60–180 cm soil profile. These results indicate that drip fertigation had a lower risk of nitrate leaching compared with CK treatment. GY and NUE of DI and FI treatments were significantly higher than those of CK and RF treatments, but DI used 25% less irrigation water than FI, resulting in higher WP. The WP of DI was increased by 6.8–7.4% and 4.2–16.0% for winter wheat and summer maize compared with FI, respectively. From the perspective of winter wheat-summer maize rotation system, the two-year average net income of DI was increased by 2.8%, 37.9% and 59.9% compared with FI, RF and CK, respectively. Therefore, deficit irrigation with nitrogen fertigation was recommended as a sustainable fertigation strategy for achieving higher grain yield, nitrogen use efficiency, water productivity and net income and reducing the risk of soil nitrate-N leaching in the winter wheat-summer maize rotation system.

Drip fertigation is beneficial to improve crop grain yield (GY), water productivity (WP) and nitrogen use efficiency (NUE), but it is not clear whether drip fertigation can improve economic benefit and how much water and nitrogen should be applied for wheat-maize rotation system in semi-humid and drought-prone regions. A two-year (2018–2020) winter wheat-summer maize rotation field experiment (including twelve drip fertigation treatments (complete combination design of three irrigation (RF: rain-fed, DI: deficit irrigation, 75% ETc, and FI: full irrigation, 100% ETc) and four nitrogen levels (N0: no nitrogen, N1: 85 kg ha−1 for wheat and 90 kg ha−1 for maize, N2: 170 kg ha−1 for wheat and 150 kg ha−1 for maize) and N3: 255 kg ha−1 for wheat and 210 kg ha−1 for maize)) and a conventional practice (Con)) was conducted to explore the response of GY, NUE, WP and net income to different water and nitrogen levels in the Guanzhong Plain of China. The results showed that water and nitrogen application levels had significant effects on GY, NUE, WP and net income of winter wheat and summer maize. For winter wheat, DIN2 (the combination of irrigation and nitrogen) achieved the highest GY (9.2 t ha−1, two-year average), WP (2.11 kg m−3) and net income (11 839 CNY ha−1). For summer maize, the highest GY (11.1 t ha−1), WP (2.32 kg m−3) and net income (14 859 CNY ha−1) were observed at DIN3, RFN3 and DIN2, respectively. For winter wheat-summer maize rotation system, the highest GY (20.2 t ha−1, winter wheat + summer maize, two-year average) and net income (26 698 CNY ha−1) were observed at DIN2; and the highest WP of 2.15 kg m−3 was obtained at RFN3, but had insignificant difference with DIN2 (2.13 kg m−3) (P > 0.05). Therefore, deficit irrigation coupled with 320 kg N ha−1 (170 kg ha−1 for wheat, 150 kg ha−1 for maize) was considered as the best drip fertigation strategy for achieving high GY, WP and net income in winter wheat-summer maize rotation system. Moreover, the response surface methodology was used to determine the optimal water consumption and nitrogen application rate based on binary quadratic regression analysis. The results showed that the GY and net income can synchronously achieve 95~100% maximum values when the water consumption ranged from 434 to 496 mm and 458–500 mm, and the nitrogen application rate ranged from 165 to 211 kg ha−1 and 187–250 kg ha−1 for winter wheat and summer maize, respectively.

Understanding the response of spike density (SD), grain number per spike (GN), and thousand kernel weight (TKW) to the application amount of nitrogen and irrigation, and clarifying the contribution of nitrogen and irrigation to the increased yield are vital for achieving high grain yield (GY), water and nitrogen use efficiency (WUE and NUE) in precision agriculture. A two-year (2018–2020) drip fertigated winter wheat experiment was conducted with three irrigation levels (rain-fed (RF), deficit irrigation (DI, 75% ETc) and full irrigation (FI, 100% ETc)) as main plot and four nitrogen levels (0 (NN), 85 (N3), 170 (N2) and 255 (N1) kg N hm−2) as subplot in Northwest China. The results showed that the tillers per plant (TP) significantly increased with increasing nitrogen application amount (0–255 kg hm−2), but the SD had insignificant difference between N1 and N2 levels due to lower effective spike rate (ESR) of N1. The GN firstly increased and then decreased with increasing nitrogen application amount. However, the TKW continued to decrease with increasing nitrogen application amount. Irrigation significantly increased SD and GN, but the impact on TKW showed uncertainty during two growing seasons. The structure equation model showed that both irrigation and nitrogen indirectly affect GY by affecting yield components, and nitrogen had the stronger influence to SD, GN and TKW than irrigation in this study. The highest GY (9.10 and 9.28 t hm−2 in 2018–2019 and 2019–2020, respectively) was observed at DIN2, which increased by 200% and 277% in 2018–2019 and 2019–2020 growing seasons compared with RFNN treatment, respectively. And among these increased yield, more than 65% and approximately 20% were contributed by the application of nitrogen and irrigation, respectively. In addition, DIN2 also obtained the highest WUE and higher NUE due to lower actual evapotranspiration and nitrogen application amount. Therefore, deficit drip irrigation (75%ETc) coupled with 170 kg N hm−2 was the best management strategy of irrigation and nitrogen under drip fertigation in Northwest China.

A pot experiment was conducted to investigate the effect of potassium (K) fertilization on tomato quality, plant K uptake, water and K use efficiency (WUE and KUE) under deficit irrigation regime. During fruit development stage of the first cluster of fruit, irrigation regimes were comprised of three levels, i.e. 80–90% field capacity (θf) (W1), 70–80% θf (W2) and 60–70% θf (W3); and K fertilization rates were also consisted of three different rates, i.e. 0 g K2O kg−1 soil (K1), 0.46 g K2O kg−1 soil (K2) and 0.92 g K2O kg−1 soil (K3). The result showed that deficit irrigation as well as increased K fertilization significantly improved quality of fruit where, soluble sugar, titratable acid and content of vitamin C were positively correlated to K concentration of leaf ([K]leaf), indicating that [K]leaf may have a role to improve fruit quality. The highest plant WUE was observed in W1 plants, which consumed the most water and produced the highest dry mass. K fertilization had no effect on WUE based on biomass, but had positive effect on K concentration and K accumulation in each tissue, hereby increased total K uptake, while decreased KUE.

Facing with the scarcity of water resource and irrational fertilizer use, it is highly important to supply plants with water and fertilizer in a coordination pattern to improve yield with high water use efficiency (WUE). A field experiment was conducted in 2012 and 2014 to investigate the effect of N supply methods on biomass accumulation and distribution, yield components and WUE of maize (Zea mays L.) under different partial root-zone irrigations in the Hexi corridor of Northwest China. Three irrigation methods included alternate furrow irrigation (AI), fixed furrow irrigation (FI) and conventional furrow irrigation (CI). Three N supply methods included alternate N supply (AN), fixed N supply (FN) and conventional N supply (CN), were applied in combination with each irrigation method. Leaf area index (LAI), shoot biomass and root length density at different growth stages, yield components, biomass distribution in different shoot organs and WUE of maize were determined. Results showed that, LAI at the R1, R2 and R4 stages, shoot biomass at the R6 stage, grain yield, harvest index (HI) and WUE of maize were significantly increased by AN or CN compared to FN in each irrigation method as well as by AI compared to CI and FI in each N supply method. Compared to CI coupled with CN (CICN), AI coupled with AN or CN (AIAN or AICN) significantly increased the LAI, shoot biomass, grain yield and WUE of maize. The biomass distribution proportion in kernel and contribution rate of the biomass transfer from other shoot organ to grain were also increased by AIAN and AICN, resulting in significantly higher HI. These increased shoot biomass accumulation and WUE were related to the enhanced LAI and root growth. AIAN and AICN also achieved a greater kernels number per cob and 1000-kernel weight compared to CICN. Thus, AI coupled with CN or AN are proposed as a better pattern of irrigation and nitrogen application with positive regulative effects on shoot biomass accumulation and distribution and WUE in the Hexi Corridor area of Northwest China and other regions with similar environments. These results can also provide a basis for in-depth understanding of the mechanism of biomass accumulation and growth responses to nitrogen supply methods.

Antioxidation responses of maize roots and leaves to water deficit and rewatering under partial root-zone irrigation (PRI) were investigated using a pot system. Plants were cultured using three irrigation methods, i.e. conventional irrigation (CI), alternate PRI (APRI) and fixed PRI (FPRI) with three different water regimes including W1 (70% field capacity, FC), W2 (50% FC) and W3 (35% FC). Compared to CI, root peroxidases (POD) activity was enhanced in the irrigated root zone of FPRI and both root zones of APRI during mild water deficit. After rewatering, POD activity was increased in the dry root zone under FPRI but reduced in the roots under APRI. Roots in the dry zone and leaves under FPRI remained high superoxide dismutase (SOD) activity after rewatering. In contrast, SOD activity decreased in the roots and leaves under CI and APRI. Malondialdehyde (MDA) contents were increased in leaves and two sub-roots under FPRI during water deficit and remained higher after rewatering compared to those under CI and APRI. MDA contents in the tissues under APRI showed similar levels to those under CI. Compared to CI, APRI showed the same biomass production, achieving significantly higher water use efficiency under mild water deficit. The results suggested that plants under APRI experienced less oxidative stress or damage induced by water deficit.

To investigate the dynamic change of plant nitrogen (N) absorption and accumulation from different root zones under the partial root-zone irrigation (PRI), maize plants were raised in split-root containers and irrigated on both halves of the container (conventional irrigation, CI), on one side only (fixed partial root-zone irrigation, FPRI), or alternatively on one of two sides (alternate partial root-zone irrigation, APRI). And the isotope-labeled 15N-(NH4)2SO4 was applied to one half of the container with (14NH4)2SO4 to the other half so that N inflow rates can be tracked. Results showed that APRI treatment increased root N absorption in the irrigated zone significantly when compared to that of CI treatment. The re-irrigated half resumed high N inflow rate within 5 days after irrigation in APRI, suggesting that APRI had significant compensatory effect on N uptake. The amount of N absorption from two root zones of APRI was equal after two rounds of alternative irrigation (20 days). The recovery rate, residual and loss percentages of fertilizer-N applied to two zones were similar. As for FPRI treatment, the N accumulation in plant was mainly from the irrigated root zone. The recovery rate and loss percentage of fertilizer-N applied to the irrigated zone was higher and the residual percentage of fertilizer-N in soil was lower if compared to those of the non-irrigated zone. The recovery rate of fertilizer-N in APRI treatment was higher than that of the non-irrigated zone but lower than that of the irrigated zone in FPRI treatment. In total, both FPRI and APRI treatments increased N and water use efficiencies but only consumed about 70% of the irrigated water when compared to CI treatment.

A field experiment was carried out to investigate the effects of different supply methods of nitrogen (N) fertilizer and irrigation on the spatial distribution and dynamics of soil NO3-N for maize (Zea mays L.) grown in northwest China in 2012 and 2014. In 2012, there were three irrigation methods: alternate furrow irrigation (AI), fixed furrow irrigation (FI) and conventional furrow irrigation (CI). Three N supply methods: alternate N supply (AN), fixed N supply (FN) and conventional N supply (CN), were applied at each irrigation method. In 2014, the fixed treatments were excluded. Soil NO3-N in horizontal direction was measured to 100 cm soil profile. For 2012, at filling stage, compared to CI, AI increased soil NO3-N concentration under the plant by 4.5 to 7.4% in 0-40 cm soil profile and decreased that by 9.9 to 14.4% in 40-80 cm for three N supply methods. NO3-N concentration between two sides of the ridge was comparable for AN and CN coupled with AI or CI. When compared to CI, AI reduced soil NO3-N concentration in 60-100 cm by 4.8 to 8.7% from 12 collars stage to maturity over different positions when coupled with CN. Soil residual NO3-N at maturityin 0-100 cm was the lowest in AI coupled with CN or AN. The 2014 experiment verified the above results. Therefore, alternate furrow irrigation coupled with conventional or alternate N supply brought an optimum spatial distribution of soil NO3-N during maize season, resulting in little soil residual NO3-N at maturity.

Effects of partial root-zone irrigation (PRI) on the hydraulic conductivity in the soil-root system (L(sr)) in different root zones were investigated using a pot experiment. Maize plants were raised in split-root containers and irrigated on both halves of the container (conventional irrigation, CI), on one side only (fixed PRI, FPRI), or alternately on one of two sides (alternate PRI, APRI). Results show that crop water consumption was significantly correlated with L(sr) in both the whole and irrigated root zones for all three irrigation methods but not with L(sr) in the non-irrigated root zone of FPRI. The total L(sr) in the irrigated root zone of two PRIs was increased by 49.0-92.0% compared with that in a half root zone of CI, suggesting that PRI has a significant compensatory effect of root water uptake. For CI, the contribution of L(sr) in a half root zone to L(sr) in the whole root zone was ∼50%. For FPRI, the L(sr) in the irrigated root zone was close to that of the whole root zone. As for APRI, the L(sr) in the irrigated root zone was greater than that of the non-irrigated root zone. In comparison, the L(sr) in the non-irrigated root zone of APRI was much higher than that in the dried zone of FPRI. The L(sr) in both the whole and irrigated root zones was linearly correlated with soil moisture in the irrigated root zone for all three irrigation methods. For the two PRI treatments, total water uptake by plants was largely determined by the soil water in the irrigated root zone. Nevertheless, the non-irrigated root zone under APRI also contributed to part of the total crop water uptake, but the continuously non-irrigated root zone under FPRI gradually ceased to contribute to crop water uptake, suggesting that it is the APRI that can make use of all the root system for water uptake, resulting in higher water use efficiency.