Taisheng Du

Deficit irrigation and sustainable water-resource strategies in agriculture for China’s food security

More than 70% of fresh water is used in agriculture in many parts of the world, but competition for domestic and industrial water use is intense. For future global food security, water use in agriculture must become sustainable. Agricultural water-use efficiency and water productivity can be improved at different points from the stomatal to the regional scale. A promising approach is the use of deficit irrigation, which can both save water and induce plant physiological regulations such as stomatal opening and reproductive and vegetative growth. At the scales of the irrigation district, the catchment, and the region, there can be many other components to a sustainable water-resources strategy. There is much interest in whether crop water use can be regulated as a function of understanding of physiological responses. If this is the case, then agricultural water resources can be reallocated to the benefit of the broader community. We summarize the extent of use and impact of deficit irrigation within China. A sustainable strategy for allocation of agricultural water resources for food security is proposed. Our intention is to build an integrative system to control crop water use during different cropping stages and actively regulate the plants growth, productivity, and development based on physiological responses. This is done with a view to improving the allocation of limited agricultural water resources.

Scaling Up Stomatal Conductance from Leaf to Canopy Using a Dual-Leaf Model for Estimating Crop Evapotranspiration

The dual-source Shuttleworth-Wallace model has been widely used to estimate and partition crop evapotranspiration (λET). Canopy stomatal conductance (Gsc), an essential parameter of the model, is often calculated by scaling up leaf stomatal conductance, considering the canopy as one single leaf in a so-called “big-leaf” model. However, Gsc can be overestimated or underestimated depending on leaf area index level in the big-leaf model, due to a non-linear stomatal response to light. A dual-leaf model, scaling up Gsc from leaf to canopy, was developed in this study. The non-linear stomata-light relationship was incorporated by dividing the canopy into sunlit and shaded fractions and calculating each fraction separately according to absorbed irradiances. The model includes: (1) the absorbed irradiance, determined by separately integrating the sunlit and shaded leaves with consideration of both beam and diffuse radiation; (2) leaf area for the sunlit and shaded fractions; and (3) a leaf conductance model that accounts for the response of stomata to PAR, vapor pressure deficit and available soil water. In contrast to the significant errors of Gsc in the big-leaf model, the predicted Gsc using the dual-leaf model had a high degree of data-model agreement; the slope of the linear regression between daytime predictions and measurements was 1.01 (R2 = 0.98), with RMSE of 0.6120 mm s−1 for four clear-sky days in different growth stages. The estimates of half-hourly λET using the dual-source dual-leaf model (DSDL) agreed well with measurements and the error was within 5% during two growing seasons of maize with differing hydrometeorological and management strategies. Moreover, the estimates of soil evaporation using the DSDL model closely matched actual measurements. Our results indicate that the DSDL model can produce more accurate estimation of Gsc and λET, compared to the big-leaf model, and thus is an effective alternative approach for estimating and partitioning λET.

Irrigation water productivity is more influenced by agronomic practice factors than by climatic factors in Hexi Corridor, Northwest China.

Quantifying the influence of driving factors on irrigation water productivity (IWP) is vital for efficient agricultural water use. This study analyzed contributions of agronomic practice and climatic factors to the changes of IWP, based on the data from 1981 to 2012 in Hexi Corridor, Northwest China. Cobb-Douglas production functions were developed by the partial least squares method and contribution rates of the driving factors were calculated. Results showed that IWP and its driving factors increased during the study period, with different changing patterns. IWP was significantly correlated with the agronomic practice factors, daily mean temperature and solar radiation of the crop growing period. The agronomic practice factors including irrigation, fertilization, agricultural film, and agricultural pesticide contributed 20.6%, 32.8%, 42.3% and 11.1% respectively to the increase of IWP; and the contribution rates of the climatic factors, i.e. daily mean temperature and solar radiation, are −0.9% and 0.9%. And the contributions of these factors changed in different sub-periods. It is concluded that agronomic practice factors influenced IWP much more than climatic factors. The improvement of IWP should rely on advanced water-saving technology and application of optimum (need-based) fertilizer, agricultural film and pesticide, ensuring efficient use of agronomic inputs in the study area.

Responses of water productivity to irrigation and N supply for hybrid maize seed production in an arid region of Northwest China

Water and nitrogen (N) are generally two of the most important factors in determining the crop productivity. Proper water and N managements are prerequisites for agriculture sustainable development in arid areas. Field experiments were conducted to study the responses of water productivity for crop yield (WPY-ET) and final biomass (WPB-ET) of film-mulched hybrid maize seed production to different irrigation and N treatments in the Hexi Corridor, Northwest China during April to September in 2013 and also during April to September in 2014. Three irrigation levels (70%–65%, 60%–55%, and 50%–45% of the field capacity) combined with three N rates (500, 400, and 300 kg N/hm2) were tested in 2013. The N treatments were adjusted to 500, 300, and 100 kg N/hm2 in 2014. Results showed that the responses of WPY-ET and WPB-ET to different irrigation amounts were different. WPY-ET was significantly reduced by lowering irrigation amounts while WPB-ET stayed relatively insensitive to irrigation amounts. However, WPY-ET and WPB-ET behaved consistently when subjected to different N treatments. There was a slight effect of reducing N input from 500 to 300 kg/hm2 on the WPY-ET and WPB-ET, however, when reducing N input to 100 kg/hm2, the values of WPY-ET and WPB-ET were significantly reduced. Water is the primary factor and N is the secondary factor in determining both yield (Y) and final biomass (B). Partial factor productivity from applied N (PFPN) was the maximum under the higher irrigation level and in lower N rate (100–300 kg N/hm2) in both years (2013 and 2014). Lowering the irrigation amount significantly reduced evapotranspiration (ET), but ET did not vary with different N rates (100–500 kg N/hm2). Both Y and B had robust linear relationships with ET, but the correlation between B and ET (R2=0.8588) was much better than that between Y and ET (R2=0.6062). When ET increased, WPY-ET linearly increased and WPB-ET decreased. Taking the indices of Y, B, WPY-ET, WPB-ET and PFPN into account, a higher irrigation level (70%–65% of the field capacity) and a lower N rate (100–300 kg N/hm2) are recommended to be a proper irrigation and N application strategy for plastic film-mulched hybrid maize seed production in arid Northwest China.

Root length density distribution and associated soil water dynamics for tomato plants under furrow irrigation in a solar greenhouse

Furrow irrigation is a traditional widely-used irrigation method in the world. Understanding the dynamics of soil water distribution is essential to developing effective furrow irrigation strategies, especially in water-limited regions. The objectives of this study are to analyze root length density distribution and to explore soil water dynamics by simulating soil water content using a HYDRUS-2D model with consideration of root water uptake for furrow irrigated tomato plants in a solar greenhouse in Northwest China. Soil water contents were also in-situ observed by the ECH2O sensors from 4 June to 19 June and from 21 June to 4 July, 2012. Results showed that the root length density of tomato plants was concentrated in the 0–50 cm soil layers, and radiated 0–18 cm toward the furrow and 0–30 cm along the bed axis. Soil water content values simulated by the HYDRUS-2D model agreed well with those observed by the ECH2O sensors, with regression coefficient of 0.988, coefficient of determination of 0.89, and index of agreement of 0.97. The HYDRUS-2D model with the calibrated parameters was then applied to explore the optimal irrigation scheduling. Infrequent irrigation with a large amount of water for each irrigation event could result in 10%–18% of the irrigation water losses. Thus we recommend high irrigation frequency with a low amount of water for each irrigation event in greenhouses for arid region. The maximum high irrigation amount and the suitable irrigation interval required to avoid plant water stress and drainage water were 34 mm and 6 days, respectively, for given daily average transpiration rate of 4.0 mm/d. To sum up, the HYDRUS-2D model with consideration of root water uptake can be used to improve irrigation scheduling for furrow irrigated tomato plants in greenhouses in arid regions.

Effects of water stress at different growth stage on greenhouse multiple-trusses tomato yield and quality

In order to explore the effects of deficit irrigation (DI) on yield and quality of solar greenhouse multiple-trusses tomato and determinate optimal deficit irrigation scheduling, a field experiment was conducted with different water deficit levels applied at three growth stages, i.e. seedling stage, flowering and fruit development stage and fruit maturation and fruit harvesting stage. The results showed that based on the normal irrigation amount of 21mm (CK), applying 1/3 or 2/3 irrigation amount of CK at seedling stage did not affect the tomato yield and quality; applying 1/3 or 2/3 irrigation amount of CK at fruit maturation and harvesting stage significantly improved tomato fruit quality, but decreased market yield by 48.2% and 38.0% respectively, which resulted in water use efficiency (WUE) drop. Considering the yield, quality and water saving amount, applying 1/3 irrigation amount of CK at the flowering and fruit development stage, normal irrigation at other growth stages, i.e. totally 12 irrigation times with 196 mm, could obtain the comprehensive objects of higher fruit quality, acceptable yield and water saving, which could be recommended as the suitable deficit irrigation scheduling for the multiple trusses tomato in solar greenhouse spring to summer season cropping season.

Notice of Retraction Evapotranspiration of Haloxylon Ammodendron Bunge and Caragana Karshiskii kom under saline irrigation

Saline irrigation decreased the evapotranspiration (ET) of Haloxylon Ammodendron Bunge (H. Ammodendron) and Caragana Karshiskii Kom (C. Karshiskii) via reducing transpiration water, and it also changed the proportion of transpiration in ET: the proportion of evaporation from soil surface increased, and the proportion of transpiration in ET decreased when irrigating with higher salt concentration. The ET, soil evaporation and transpiration of H. Ammodendron irrigated with salinity of 7g/L and 12g/L reduced by 20% and 42%, 1.97% and 12%, 24% and 50% respectively compared to the plants irrigated with freshwater, while the reductions for C Karshiskii were 27% and 38%, 17% and 18%, 31% and 44%, respectively.