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Highlights: [•] ET c of summer maize showed a significant downward trend during 1960–2009 in the HHH farming region. [•] The variation of ET aw did not drop significantly due to yearly fluctuation of the effective rainfall in the growing season. [•] ET c was higher in the eastern regions and lower in the western in the HHH farming region. [•] The decrease of solar radiation contributed most to the decrease of the summer maize ET c . [Copyright &y& Elsevier]

• Cotton ET c showed a significant declining trend during the past five decades in North China Plain. • Rainfall-crop compatibility index in cotton growing season reached 75% with applied irrigation of 122 mm. • The spatially maximum cotton ET c shifted from southern in 1965-1975 to northeastern then western by 2006-2016. • The decline in solar radiation, sunshine hours and wind speed were responsible for the decline of cotton ET c. Climate change directly affects crop evapotranspiration and irrigation demand. The temporal and spatial variation of crop evapotranspiration is crucial to irrigation schedule planning and water resource management. Using 52 years of climate data from 43 stations in the North China Plain, this study examined trends and spatial distributions of the cotton evapotranspiration (ET c) and irrigation requirement (I wr) and revealed the impact of climate variation on cotton ET c change. We found that, annual ET c of cotton in the growing season showed a significant declining trend, which decreased from 606 mm yr−1 in 1965-1975 to 551 mm yr−1 in 2006-2016. Annual effective rainfall (R e) and I wr of cotton's growing season did not show consistency over the 52 year period, which averaged at 451 mm (441∼ 466 mm) and 122 mm (105 ∼ 145 mm), respectively. The 75% of cotton ET c was supplied by rainfall and 25% by irrigation water. This is much better than for winter wheat where 60% must be supplied by irrigation. The location of the spatial maximum cotton ET c shifted during the past five decades. From 1965 to 1975, maximum ET c values were found in the southern part and then shifted to the northeastern part from 1976 to 1985. During the period of 1986 to 2005, maximum ET c occurred in the middle area and shifted to the western part in 2006-2016. During the past five decades, solar radiation, sunshine hours and wind speed decreased significantly resulting in a significant decrease in ET c at −1.1 mm yr−1. This study highlights the indispensable information of water requirements for future irrigation scheduling of cotton in the North China Plain. [ABSTRACT FROM AUTHOR]

Over-irrigation to ensure high crop yields in North China Plain (NCP) has led to a sharp groundwater table decline over the past decades. We conducted a scenario analysis from1980 to 2017 with 12 irrigation strategies from T1W0M0 to T12W3M2 (T is treatment and numbers of irrigation times in wheat (W) and maize (M) seasons, 75 mm each) for the dominant winter wheat-summer maize rotation using the soil-water-atmosphere-plant (SWAP) model in the NCP. After model calibration and validation with 4-year experimental data, we analyzed the long-term simulated annual crop yield, actual evapotranspiration (ET a), water productivity (WP), groundwater table change and economic benefit to the different irrigation practices. The optimized irrigation strategy is based on an integral analysis for different precipitation year-types. Results showed that annual yield and WP increased with increased irrigation until these reached a plateau. Treatment T4W2M1 was the turning point with an annual yield of 15335 kg·ha-1, significantly higher than T2W1M1 (26 %) and T1W0M0 (63 %), but not significantly different from 4 to 5 irrigations in wet and normal years. ET a increased with increased irrigation from 456 to 644 mm yr-1. The annual WP followed a similar trend as annual crop yield for all irrigation schedules. T4W2M1 had an annual WP of 2.47 kg cm-3, significantly higher by 15 % than T2W1M1 and 24 % higher than T1W0M0, with no significant difference seen with 4–5 irrigations. The rainfed treatment mitigated groundwater table decline the best, even reversing the trend during the past four decades to 0.11 m yr-1 rise. This was followed by two irrigation treatments (−0.30 m yr-1), three irrigations (−0.55 m yr-1), four irrigations (−0.72 m yr-1), and five irrigations (−0.86 m yr-1). The latter corresponds to typical farmer practice. Using the productivity indicators, including irrigation WP, marginal benefit and economic index, T4W2M1 showed the best performance. Therefore, we recommend T4W2M1 (two irrigations at pre-wintering and jointing stages for wheat and one irrigation at maize sowing stage) as the best irrigation strategy for the wheat-maize rotation to mitigate groundwater table decline, and sustain grain yields and water productivity in the NCP; another anthesis irrigation for winter wheat is recommended during extreme dry years to sustain grain yield. • Twelve irrigation strategies for wheat-maize from 1980 to 2017 were evaluated. • Three targeted irrigations per year mitigated the groundwater table decline by 40 %. • 225 mm total for three irrigations per year is best to increase water productivity. [ABSTRACT FROM AUTHOR]

Reduced irrigation generally induces the tomato fruit yield reduction but enhance the fruit quality. Elevated CO 2 (eCO 2) injection is a common technique for alleviating water stress while eCO 2 could inevitably lead to the element concentration dilution in the plant organs. Inoculated with photosynthetic bacteria (PSB) are confirmed to form a symbiotic relationship with crop roots, thereby promoting root development, and improving crop root nutrient and water uptake capacity. Yet, it remains unknown whether PSB could mitigate the adversely effect of nutrient dilution under eCO 2 condition and the yield decline under reduced irrigation. To investigate that, two water treatments, including reduced irrigation (RI, plants were irrigated to 75% field water capacity) and full irrigation (FI, plants were irrigated to 90% field water capacity) of tomato plants, were grown under normal ambient CO 2 (aCO 2 , 400 ppm) and elevated CO 2 (eCO 2 , 800 ppm) conditions, respectively. And photosynthetic bacteria were inoculated in half plants. The results showed that inoculation of PSB improved the effectiveness of CO 2 stimulation on biomass and yield in tomato plants grown under reduced irrigation conditions. The stimulation effects have been associated with increased advantages linked to their root system, we have observed that CO 2 and PSB inoculation promoted the root development and antioxidant abilities. These consequently increased nitrogen uptake efficiency under eCO 2 and reduced irrigation conditions, and increased nitrogen accumulation in various organs. Furthermore, eCO 2 and inoculation with PSB individually or in combination ameliorated yield penalties under reduced irrigation conditions. Combined elevated CO 2 and inoculation with PSB resulted in the highest fruit quality. Collectively, the responses of tomato fruit yield and quality to water-reduced irrigation regimes are further enhanced by the combination of eCO 2 and PSB inoculation, and this would be efficacious in greenhouse tomato cultivation and future agriculture production. • The combined effect of PSB and eCO 2 on cherry tomato treated with reduced irrigation were studied. • The combination of PSB and eCO 2 compensated the negative effect on tomato root limitation induced by low water treatments. • The responses of tomato fruit yield and quality to reduced irrigation are enhanced by combination of PSB and eCO 2. [ABSTRACT FROM AUTHOR]

The water-intensive conventional winter wheat–summer maize (WM) double cropping system in the North China Plain (NCP) has significantly decreased the groundwater table. To address this issue, we undertook a two-year field experiment to explore the potential and mechanisms of water-saving and yield increase of five newly designed diversified crop rotations incorporating spring crops (sweet potato, soybean, peanut, spring maize, and millet) into cereal crops compared with the conventional WM (as control). The results revealed that the five diversified crop rotations significantly decreased annual actual crop evapotranspiration by 7–12% and net groundwater use by 21–31% compared to the conventional WM. Sweet potato and peanut-based rotations significantly enhanced annual average equivalent yields up to 32% and economic benefit (+50%, +7%) while improving water productivity by 24–68% compared to WM. Shallow-rooted crops (sweet potato, soybean, peanut, and millet), when used as the preceding crop, improved soil water storage in the 0–180 cm soil layer at the start of the succeeding wheat planting season by 3–9% compared to the conventional WM. These shallow-rooted crops mainly concentrated their root systems in the 0–120 cm soil water, particularly the top 80 cm, complementing the deeper root systems of wheat, which extended down to 180 cm. Consequently, this optimal soil water use regime in diversified crop rotations increased the leaf area index and aboveground biomass of the succeeding wheat and maize crops, increasing total grain yields by 4–11%. Thus, introducing shallowed-root annual crops as preceding crops to the current WM rotation is beneficial for decreasing irrigation inputs, enhancing overall crop productivity, and mitigating groundwater table decline in the NCP. • Diversified crop rotations significantly decreased annual ET a and net groundwater use. • Shallow-rooted crops rotated deep-rooted crops produced soil moisture complementarity. • Diversified preceding crops had a positive 'lag effect' on the grain yield of succeeding cereals. [ABSTRACT FROM AUTHOR]

Agricultural intensification has increased crop productivity but simplified production and reduced cropping system diversity. In recent decades, the intensified wheat–maize rotation in the North China Plain has sharply decreased the groundwater table, with associated environmental and biodiversity issues. Understanding whether increasing cropping system diversity stabilizes productivity, improves resilience, and reduces adverse environmental impacts is critical. This study quantified the water requirements of nine staple crops from 1960 to 2020, established 15 alternative crop rotations, and evaluated the resilience of each rotation in the Cangzhou area, a typical groundwater deletion funnel area. The results showed that reducing cropping density (harvests per year) from 2 to 1.5 decreased the average annual water requirement and irrigation demand by 14 % and 33 %, respectively. Summer soybean alternated with maize and rotated with wheat did not reduce groundwater use but increased profitability and protein production. Spring mung bean–summer millet-based multi-rotations had higher precipitation coupling degrees (8 % in wet years, 17 % in normal years, and 56 % in dry years) and profitability (1.1–2.4 times) than the wheat–maize rotation. The spring potato–summer millet rotation in one year had the greatest profitability, the highest equivalent yield to wheat, and the highest water use efficiency (WUE), while spring maize rotated with winter wheat–summer soybean performed best for protein content, energy output, and WUEs. This study identified 11 alternative rotations with a higher comprehensive evaluation index than the conventional wheat–maize rotation based on entropy-TOPSIS considering 12 indicators. Spring mungbean is not suitable for inclusion in the crop rotation when solely cultivated in one year due to mismatched rainfall. Beyond wheat and maize, soybean, millet, and potato are promising crops for innovative multi-year multi-crop rotations to enhance crop diversification, maximize system outputs, and minimize groundwater and energy depletion. This study's analysis could be extended to develop robust and diverse crop rotations with multiple co-benefits in other water-stressed agricultural regions. • Water requirements of nine staple crops from 1960 to 2020 was quantified. • 15 diversified crop rotations were redesigned and established. • Multi-dimensional outcomes of each rotation were evaluated for synergies and tradeoff. • Reducing cropping density mitigated groundwater table decline. • Wheat-maize rotations involving soybean, millet and potato achieved multiple co-benefits. [ABSTRACT FROM AUTHOR]