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Exploring the impacts of CO2 and soil water availability on the photosynthetic performance and water use efficiency of three green manure plants could provide theoretical basis for the adaptive management of grassland ecosystems under future climate change. An experiment was conducted in an artificial climate chamber with precisely controled CO2 concentrations of 400 (natural atmospheric) and 800 µmol · mol-1 (doubled), and four water treatments, 80% field water holding capacity (FC) (full irrigation control group), 55%-60% FC (mild water deficit), 35%-40% FC (moderate water deficit), <35% FC (severe water deficit) to investigate the impacts of increasing CO2 concentration and water deficit on chlorophyll content, gas exchange variables, and water use efficiency (WUE) of oilseed rape (Brassica napus), white clover (Trifolium repens), and alfalfa (Medicago sativa). The results showed that under the same CO2 concentration, when soil moisture was less than 40% FC, the chlorophyll content and gas exchange parameters of three plants were significantly decreased. The treatment of 55%-60% FC did not alter the total chlorophyll content of three species, but reduced the photosynthetic rate (Pn) and transpiration rate (Tr) of white clover and alfalfa by 6%-25% and did not affect their WUE. Compared with atmospheric CO2 concentration, the doubled CO2 concentration significantly decreased the Pn of oilseed rape by 21.5% under the full irrigation treatment, increased the Pn of three species under mild water deficit, increased the Pn of oilseed rape and alfalfa under moderate water deficit, but only improved the Pn of alialfa under severe water deficit. The doubled CO2 concentration significantly increased WUE of white clover and alfalfa under all water deficit conditions, but only increased WUE of oilseed rape under mild water deficit. Increasing CO2 concentration and water deficit significantly interacted to affect Pn of three species and the WUE of oilseed rape. In summary, the three species differed in their responses to doubled atmospheric CO2 concentration and different levels of water deficit. Our results suggested that elevated CO2 concentration could improve the adverse effects of mild water deficit on photosynthetic performance and WUE of three species, but only improve the photosynthetic performance of alfalfa under severe water deficit. [ABSTRACT FROM AUTHOR]

The leal distribution in intercropping canopy is usually laterally and vertically heterogeneous, which makes continuous measurement ol light interception very difficult. In order to quantily the light interception by wheat/maize intercropping during different growth stages, a geometrical model was developed in this study to simulate photosynthetically active radiation (PAR) transmission in this system. Measured PAR values in field experiments were used to validate the geometrical model. Results showed that the geometrical model efficiently simulated the PAR transmitted on soil surface under intercropping canopy. The determination coefficients ol linear regression between estimated and measured values were 0.947 and 0.950 for 6:2 intercropping (I62) and 12:4 intercropping (I124), respectively. The values of PAR intercepted by I62 intercropping system in 2012 and 2013 were 1061.4 and 924.3 MJ . m-2, respectively, which were the highest among all cropping systems. The radiation caption ratios (RCRs) of I62 and I124 relative to sole crops were 1.29 and 1.19 during 2012 growing season, and 1.21 and 1.16 during 2013 growing season, respectively. [ABSTRACT FROM AUTHOR]

Soil moisture is a key factor affecting jujube growth in the semiarid Northern Shaanxi Province. The impacts of different engineering and mulching measures on soil moisture were investigated via in situ measurements in a typical dryland jujube orchard. The results showed that the mean soil moistures (0-180 cm) of scale-like pit + branch mulching, scale-like scale + straw mulching, and soil moisture of scale-like pit with no mulching were increased by 14. 2% , 9. 4% , and 4. 8% than control, respectively. Different measures, especially for the scale-like pit + branch mulching, significantly increased the soil moisture in the soil surface (0-20 cm) and the main root zone layer (20-100 cm) during the jujube growth stage. Individual precipitation events had great impacts on soil moisture in the 0-100 cm, while its effect on soil moisture in deep layers was not apparent. There was no significant difference among the soil moistures in different soil depths of scale-like pit with no mulching when compared with the control under high, medium, and low soil humidity conditions. This study indicated that using the clipped jujube branches as mulching could both save materials cost and achieve the goal of reserving more water in dryland jujube orchard in north Shaanxi Province. [ABSTRACT FROM AUTHOR]

The soil water storage, growth development, biomass and yield in maize/ soybean intercropping system under different separation methods were measured to analyze the resource competition of the intercropping crops. The treatments included no shoot or root separation (T1 ), shoot and root separation (T2 ), only root separation (T3 ), and only shoot separation (T4 ). Results indicated that compared to others, the average soil moisture content in the 0-120 cm soil layer decreased by 3. 1% -12. 9% in maize line, and by 2. 8% -12. 5% in soybean line for T1 . Compared to T1 , maize growth stage in T2 , T3 and T4 came late, and the plant height, leaf area and cumulative total biomass, yield and yield components all decreased, while the trends found for soybean were the opposite. In summary, the changes of crop growth and yield in the maize/ soybean intercropping system were driven by the interactions of above- and below-ground parts, and the below-ground part played a more important role. [ABSTRACT FROM AUTHOR]

Background The disproportionate distribution of arable land and water resources has become a bottleneck for guaranteeing food security in China. Virtual water and virtual water trade theory have provided a potential solution to improve water resources management in agriculture and alleviate water crises in water-scarce regions. The present study evaluates the green and blue virtual water content of wheat, maize and rice at the regional scale in China. It then assesses the water-saving benefits of virtual water flows related to the transfer of the three crops between regions. Results The national average virtual water content of wheat, maize and rice were 1071 m3 per ton (50.98% green water, 49.02% blue water ), 830 m3 per ton (76.27% green water, 23.73% blue water) and 1294 m3 per ton (61.90% green water, 38.10% blue water), respectively. With the regional transfer of wheat, maize and rice, virtual water flows reached 30.08 Gm3 (59.91% green water, 40.09% blue water). Meanwhile, China saved 11.47 Gm3 green water, while it consumed 7.84 Gm3 more blue water than with a no-grain transfer scenario in 2009. Conclusion In order to guarantee food security in China, the government should improve water productivity (reduce virtual water content of crops) during the grain production process. Meanwhile, under the preconditions of economic feasibility and land-water resources availability, China should guarantee the grain-sown area in southern regions for taking full advantage of green water resources and to alleviate the pressure on water resources. © 2012 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

Based on the multi-disciplinary researches, and in terms of the transformation efficiency of surface water to soil water, availability of cropland soil water, crop canopy structure, total irrigation volume needed on a given area, and crop yield, this paper discussed the water-saving mechanisms of intercropping system in improving cropland water use efficiency. Intercropping system could promote the full use of cropland water by plant roots, increase the water storage in root zone, reduce the inter-row evaporation and control excessive transpiration, and create a special microclimate advantageous to the plant growth and development. In addition, intercropping system could optimize source-sink relationship, provide a sound foundation for intensively utilizing resources temporally and spatially, and increase the crop yield per unit area greatly without increase of water consumption, so as to promote the crop water use efficiency effectively. [ABSTRACT FROM AUTHOR]

A field experiment was conducted at the Yuzhou Experimental Base of Henan Province to study the effects of different application rates (0, 30, 60, and 90 kg·hm-2) of water-retaining agent (WRA) on the root physiological characteristics, biomass, and grain yield of two winter wheat cultivars Zhengmai-9694 and Aikang-58, aimed to probe into the action mechanisms of WRA on the root system of winter wheat at its different growth stages. The application of WRA decreased the root membrane permeability and soluble sugar content, and increased the root vigor. After the application of WRA, the Zhengmai-9694 at its different growth stages had a greater decrement of root membrane permeability, compared with Aikang-58. In all treatments except 90 kg·hm-2 of WRA, the root vigor of Aikang-58 was obviously higher than that of Zhengmai-9694. At booting and grain-filling stages, the root soluble sugar content of Zhengmai-9694 decreased much more than that of Aikang-58. In the whole growth period of the two cultivars, their root membrane permeability and soluble sugar content were the lowest in treatment 60 kg·hm-2 of WRA, and no significant differences were observed between treatments 60 and 90 kg·hm-2 of WRA. The root vigor of Zhengmai-9694 increased remarkably with the increasing rate of WRA application, while that of Aikang-58 was the highest in treatment 60 kg·hm-2 of WRA. The application of WRA also increased root biomass, and at jointing and booting stages, the root biomass of Aikang-58 was much higher than that of Zhengmai-9694. However, at grain-filling stage, the biomass of Aikang-58 in treatments 60 and 90 kg·hm-2 of WRA was lower than that of Zhengmai-9694. Treatment 60 kg·hm-2 of WRA had the highest grain yield of the two cultivars. It was concluded that WRA had more significant effects on Zhengmai-9694 than on Aikang-58, and applying 60 kg·hm-2 of WRA could obtain the best effect. [ABSTRACT FROM AUTHOR]

To clarify the desiccation effect of deep soil and water footprint of crop production in two typical dry-farming apple orchards on the Loess Plateau of China, with Luochuan County in semi-humid region and Mizhi County in semi-arid region as two typical apple planting areas, we used the WinEPIC model to quantitatively simulate and analyze the variations of soil moisture from 0 to 15 m and water footprint of apple production during 1980-2020. The results showed that annual yield of mature orchards in Luochuan and Mizhi followed an "S" curve, with the average annual values being 24.64 and 18.42 t·hm -2 , respectively. The average annual evapotranspirations of Luochuan and Mizhi were 623.82 and 458.97 mm, the average annual drought stress days of Luochuan and Mizhi were 20.4 and 52.73 days, and the water overconsumption were 167.94 and 121.15 mm, respectively. The available soil water contents in Luochuan and Mizhi showed a sharp decline from 1 to 25 years old and from 1 to 23 years old, respectively, with average annual soil desiccation rates being 64.6 and 68.03 mm·a -1 , respectively. The dry layer of deep soil for the orchards of Luochuan and Mizhi appeared at the 13th and 7th years, and would be stable after 23 and 22 years, respectively. The formation and stability time of the soil dry layer in the area with high precipita-tion was later than that with low precipitation. Long-term soil moisture deficit would result in irreversible soil dry layer. Water footprint of apple production in Luochuan and Mizhi were low in the early stage and high in the later stage, with the average annual values being 0.187 and 0.194 m 3 ·kg -1 , respectively. Both apple yield and production water footprint were affected by precipitation. To ensure the sustainable and healthy development of apple industry, it was recommended that the optimal planting age of apple trees is about 23 years on the Loess Plateau where water sources is limited, and the maximum should not exceed 25 years.

In recent decades, extreme climate occurred frequently on the Loess Plateau. It is thus particularly important to study and predict the occurrence of extreme climate. Available researches on extreme climate mainly focus on the changing characteristics of the event itself, but ignore the correlation between average temperature and its changing trend. We used linear trend estimation, Mann-Kendall test, sliding t test and Pearson correlation analy-sis to study the variation trend of extreme temperature and its correlation with average temperature on the Loess Plateau based on the daily maximum temperature, minimum temperature and average temperature data of 79 meteo-rological stations from 1986 to 2019. The results showed that the extreme warmth index in the Loess Plateau region showed a significant upward trend, the extreme cold index showed a significant downward trend, and the frequency of extreme high temperature events increased. Most of the extreme temperature indices had abrupt changes in the middle and late 1990s and in 2012, and the extreme temperature showed a downward trend from 1998 to 2012, which better responded to the phenomenon of global warming hiatus. The increasing trend of mean temperature in the gully region, the rocky mountain region and the valley plain region was more obvious than that in other regions. The stations with large trend of extreme temperature index almost all occurred in the region with large increases of mean temperature. The increases of average temperature in small increments increased the frequency of extreme high temperature event, with the change range of extreme low temperature and its rate being greater than the extreme high temperature. Climate warming on extreme temperature index had a different effect, small changes in the average temperature in the Loess Plateau made the climate transfer towards the direction of more frequent heat.

Exploring the impacts of CO 2 and soil water availability on the photosynthetic performance and water use efficiency of three green manure plants could provide theoretical basis for the adaptive management of grassland ecosystems under future climate change. An experiment was conducted in an artificial climate chamber with precisely controled CO 2 concentrations of 400 (natural atmospheric) and 800 μmol·mol -1 (doubled), and four water treatments, 80% field water holding capacity (FC) (full irrigation control group), 55%-60% FC (mild water deficit), 35%-40% FC (moderate water deficit), &lt;35% FC (severe water deficit) to investigate the impacts of increasing CO 2 concentration and water deficit on chlorophyll content, gas exchange variables, and water use efficiency (WUE) of oilseed rape ( Brassica napus ), white clover ( Trifolium repens ), and alfalfa ( Medicago sativa ). The results showed that under the same CO 2 concentration, when soil moisture was less than 40% FC, the chlorophyll content and gas exchange parameters of three plants were significantly decreased. The treatment of 55%-60% FC did not alter the total chlorophyll content of three species, but reduced the photosynthetic rate ( P n ) and transpiration rate ( T r ) of white clover and alfalfa by 6%-25% and did not affect their WUE. Compared with atmospheric CO 2 concentration, the doubled CO 2 concentration significantly decreased the P n of oilseed rape by 21.5% under the full irrigation treatment, increased the P n of three species under mild water deficit, increased the P n of oilseed rape and alfalfa under moderate water deficit, but only improved the P n of alfalfa under severe water deficit. The doubled CO 2 concentration significantly increased WUE of white clover and alfalfa under all water deficit conditions, but only increased WUE of oilseed rape under mild water deficit. Increasing CO 2 concentration and water deficit significantly interacted to affect P n of three species and the WUE of oilseed rape. In summary, the three species differed in their responses to doubled atmospheric CO 2 concentration and different levels of water deficit. Our results suggested that elevated CO 2 concentration could improve the adverse effects of mild water deficit on photosynthetic performance and WUE of three species, but only improve the photosynthetic performance of alfalfa under severe water deficit.

The WinEPIC model was used to simulate the dynamics of soil moisture and water productivity in the deep layer of the dry farm apple orchard of Changwu in the Loess Plateau from 1980 to 2018, aiming to provide a scientific basis for the sustainable development of apple production in the area. The results showed that the average annual yield of apple orchards in Changwu area was 27.37 t·hm -2 , the average annual evapotranspiration was 673.66 mm, and the average annual water productivity was 4.07 kg·m -3 . The number of water stress days in adult apple trees was mainly affected by rainfall. The average number of stress days in the late stage of apple tree growth was 46.46 d. The soil water content in deep layer began to approach withering humidity as early as 9-year-old apple trees. Water supply in the whole growing season of Changwu area was the dominant factor impacting the yield of orchards. The reduction of effective soil water content in deep soil was the main factor restricting yield enhancement in the middle and late growth stages of apple trees. When there was no sufficient precipitation, apple trees would use soil water from deeper soil layer. Excessive precipitation could not be used by apple trees but could be converted into shallow soil moisture and evaporation if the deep layer had less available water. For the mature apple trees, less than 500 mm or higher than 700 mm of annual water supply would cause a decline in production. For apple orchard at different growth periods, water management strategy should be adjusted according to rainfall conditions in different years. Supplementary irrigation, rainwater retention, covering, and pruning of branches could be used to reduce the unproductive and luxury water consumption of apple trees, delay the appearance of deep dry layer of soil, and avoid the waste of water resources while ensuring the growth of apple trees.

To investigate the effects of intercropped rape and film mulching on soil water content in dryland apple orchards during the low-water consumption period on the Loess Plateau, soil water content and soil water storage were measured with in situ field observations. The results showed that at the sprout period of apple trees, mean water content in 0-200 cm soil layer under apple trees with film mulching + intercropping 50% width rape (PR 1 ) and apple trees with film mulching + intercropping 100% width rape (PR 2 ) treatments increased by 7.9% and 6.9% compared with the control (apple trees without film mulching+row clearing), respectively. At the blossom period of apple trees, mean soil water content under these two treatments increased by 3.5% and 6.9%, respectively. At the sprout period of apple trees, soil water competition between apple trees and rape occurred in both PR 1 and PR 2 treatments, with the competition being most severe at the boundaries. At the sprout period, competition in the PR 1 treatment was less intense than that in the PR 2 treatment. At the blossom period, competition in the PR 1 treatment was not obvious, but the competition in the PR 2 treatment was significant. Moreover, at the sprout and blossom period, a low-soil-water-content zone was observed in the PR 2 treatment. Compared with the control, both PR 1 and PR 2 treatments increased soil water storage in 0-80 cm layer, and soil water was not deficit in the 0-200 cm layer. In conclusion, the implementation of PR 1 model is conducive to improve soil water availability in the dryland apple orchard on the Loess Plateau during the low-water consumption period.

Soil water availability is a key factor restricting the ecological construction and sustainable land use in the loess hilly region. It is of great theoretical and practical significance to understand the soil moisture status of different land use types for the vegetation restoration and the effective utilization of land resources in this area. In this study, EC-5 soil moisture sensors were used to continuously monitor the soil moisture content in the 0-160 cm soil profile in the slope cropland, terraced fields, jujube orchard, and grassland during the growing season (from May to October) in the Yuanzegou catchment on the Loess Plateau, to investigate soil moisture dynamics in these four typical land use types. The results showed that there were differences in seasonal variation, water storage characteristics, and vertical distribution of soil moisture under different land use types in both the normal precipitation (2014) and dry (2015) years. The terraced fields showed good water retention capacity in the dry year, with the average soil moisture content of 0-60 cm soil layer in the growing season being 2.6%, 4.2%, and 1.8% higher than that of the slope cropland, jujube orchard, and grassland (all P<0.05). The water storage of 0-160 cm soil profile was 43.90, 32.08, and 18.69 mm higher than that of slope cropland, jujube orchard, and grassland, respectively. In the normal precipitation year, the average soil moisture content of 0-60 cm soil layer in jujube orchard in the growing season was 2.9%, 3.8%, and 4.5% lower than that of slope cropland, terraced fields, and grassland, respectively (all P<0.05). In the dry year, the effective soil water storage of 0-160 cm soil profile in the jujube orchard accounted for 35.0% of the total soil water storage. The grey relational grade between the soil moisture in the surface layer (0-20 cm) and soil moisture in the middle layer (20-100 cm) under different land use types was large, and the trend for the similarity degree of soil moisture variation followed terraced fields > grassland > slope cropland > jujube orchard. The slope cropland in this area could be transformed into terraced fields to improve the utilization of precipitation and promote the construction of ecological agriculture. Aiming at resolving the severe water shortage in the rain-fed jujube orchard for the sustainable development of jujube orchard in the loess hilly region, appropriate water management measures should be taken to reduce the water consumption of jujube trees and other inefficient water consumption.

Water scarcity is a critical factor influencing rain-fed agricultural production on the Loess Plateau, and the exploitation of rainwater is an effective avenue to alleviate water scarcity in this area. This study was conducted to investigate the spatial and temporal distribution of soil moisture in the 0-300 cm under a 21-year-old apple orchard with the rainwater collection and infiltration (RWCI) system by using a time domain reflectometer (TDR) probe on the Loess Plateau. The results showed that there was a low soil moisture zone in the 40-80 cm under the CK, and the RWCI system significantly increased soil moisture in this depth interval. Over this depth, the annual average soil moisture under RWCI 40 , RWCI 60 and RWCI 80 was 39.2%, 47.2% and 29.1% higher than that of bare slope (BS) and 75.3%, 85.4% and 62.7% higher than that of CK, respectively. The maximum infiltration depth of water under RWCI 40 , RWCI 60 and RWCI 80 was 80 cm, 120 cm and 180 cm, respectively, and the soil moisture in the 0-60, 0-100 and 0-120 cm was more affected by RWCI 40 , RWCI 60 and RWCI 80 , respectively. Over the whole growth period of apple tree, the maximum value of soil moisture content in the 0-300 cm existed in the RWCI 80 treatment, followed by the RWCI 40 and RWCI 60 treatments. Overall, the RWCI system is an effective meaning of transforming rainwater to available water resources and realizing efficient use of agricultural water on the Loess Plateau.

Soil moisture variation in dryland sloping jujube. orchard was investigated after introducing two economic crops, i.e., feed Brassica napus (JR) and Hemerocallis fulva (JH) planted between jujube rows. Jujube tree without inter-row crop was set as control (CK). The results showed that mean soil moisture for JR and JH in the 0-180 cm soil layer increased by 6.2% and 10.1% compared with CK, respectively. Soil moisture changed mainly in the 0-60 cm soil layer in growth stage of Jujube trees. Soil moisture in JR and JH treatments significantly increased in the 0-60 cm soil layer, which could meet the demand in water resource of jujube plantation. The water consumption of jujube trees also mainly concentrated in the 0-60 cm soil layer. There was a significant decay exponential relationship between the soil moisture in the 0-20 cm layer and the drought duration after rainfall. During the 18-day dry period after rain, the soil moisture contents of JR and JH were apparently higher than that of CK. In conclusion, the jujube-crop intercropping system improved the soil moisture condition. It was an effective measure to overcome the seasonal drought in jujube orchards on the loess hilly region.

The leaf distribution in intercropping canopy is usually laterally and vertically heterogeneous, which makes continuous measurement of light interception very difficult. In order to quantify the light interception by wheat/maize intercropping during different growth stages, a geometrical model was developed in this study to simulate photosynthetically active radiation (PAR) transmission in this system. Measured PAR values in field experiments were used to validate the geometrical model. Results showed that the geometrical model efficiently simulated the PAR transmitted on soil surface under intercropping canopy. The determination coefficients of linear regression between estimated and measured values were 0.947 and 0.950 for 6:2 intercropping (I62) and 12:4 intercropping (I124), respectively. The values of PAR intercepted by I62 intercropping system in 2012 and 2013 were 1061.4 and 924.3 MJ · m(-2), respectively, which were the highest among all cropping systems. The radiation caption ratios (RCRs) of I62 and I124 relative to sole crops were 1.29 and 1.19 during 2012 growing season, and 1.21 and 1.16 during 2013 growing season, respectively.

The soil water storage, growth development, biomass and yield in maize/soybean intercropping system under different separation methods were measured to analyze the resource competition of the intercropping crops. The treatments included no shoot or root separation (T1), shoot and root separation (T2), only root separation (T3), and only shoot separation (T4). Results indicated that compared to others, the average soil moisture content in the 0-120 cm soil layer decreased by 3.1%-12.9% in maize line, and by 2.8%-12.5% in soybean line for T1. Compared to T1, maize growth stage in T2, T3 and T4 came late, and the plant height, leaf area and cumulative total biomass, yield and yield components all decreased, while the trends found for soybean were the opposite. In summary, the changes of crop growth and yield in the maize/soybean intercropping system were driven by the interactions of above- and below-ground parts, and the below-ground part played a more important role.