Different Deficit Irrigation Lower Limits and Irrigation Quotas Affect the Yield and Water Use Efficiency of Winter Wheat by Regulating Photosynthetic Characteristics

To determine suitable thresholds for deficit irrigation of winter wheat in the well-irrigated area of the Huang-Huai-Hai Plain,we investigated the effects of different deficit irrigation lower limits and quotas on the photosynthetic characteristics and grain yield of winter wheat.Four irrigation lower limits were set for initiating irrigation(i.e.,light drought(LD,50%,55%,60%and 50%of field holding capacity(FC)at the seedling-regreening,jointing,heading and filling-ripening stages,respectively),medium drought(MD,40%,50%,55%and 45%of FC at the same stages,respectively),adequate moisture(CK1,60%,65%,70%and 60%of FC at the same stages,respectively),heavy drought(CK2,35%,40%,45%and 40%of FC at the same stages,respectively))and five irrigation quota per event(30,60,90,120 and 180 mm)were set for each lower limit.We found that the increase of drought stress is conducive to normal photosynthesis of winter wheat leaves which is supported by the following findings.First,photosynthetic rate(Pn)of LD60 treatment was higher than that of LD30,LD90,LD120,LD180,MD30,MD60,MD90,MD120 and MD180.Then,Under the 90 mm irrigation quota treatment,the yield of winter wheat basically increased with the increase of irrigation’s lower limit.Moreover,With the increase in irrigation quota,the yield of winter wheat increased,and the water use efficiency(WUE)of winter wheat increased at first and then decreased.In addition,compared with the LD30,MD30,MD60,MD90,MD120,and MD180,the yield of winter wheat in LD60 treatment increased by about 3.23%(3-year average),32.3%,19.9%,11.7%,10.1%,and 14.6%.At the same time,the WUE with LD60 treatment of winter wheat was significantly higher than LD90,LD120,LD180,MD30,MD60,MD90,MD120,MD180 treatments.There was a positive correlation between soil volumetric water content and Pn and between yield and Pn.The key period for yield formation in winter wheat is 180 days after sowing.In conclusion,to achieve the dual goals of stable winter wheat yield and efficient utilization of water resources in this region,the suitable threshold for initiating deficit irrigation of winter wheat is the LD60 treatment.This conclusion provides data support for water-saving and stable yield of winter wheat in this area.

Effect of Limited Single Irrigation on Yield of Winter Wheat and Spring Maize Relay Intercropping

A field experiment was conducted during the 2002/2003 cropping season of winter wheat （Triticum aestivum） and spring maize （Zea mays） to evaluate the effect of limited single drip irrigation on the yield and water use of both crops under relay intercropping in a semi-arid area of northwestern China. A controlled 35 mm single irrigation, either early or late, was applied to each crop at a certain growth stage. Soil water, leaf area, final grain yield and yield components such as the thousand-grain weight, length of spike, fertile spikelet number, number of grains per spike, and grain weight per spike were measured, and water use efficiency and leaf area index were calculated for the irrigated and non-irrigated relay intercropping treatments and sole cropping controls. The results showed that yield, yield components, water use efficiency, and leaf area index in the relay intercropping treatments were affected by limited single drip irrigation during various growth stages of wheat and maize. The total yields in the relay intercropping treatment irrigated during the heading stage of wheat and the heading and anthesis stage of maize were the highest among all the treatments, followed by that irrigated during the anthesis stage of wheat and silking stage of maize; so was the water use efficiency. Significant differences occurred in most yield components between the irrigated and non-irrigated relay-intercropping treatments. The dynamics of the leaf area index in the relay-intercropped or solely cropped wheat and maize showed a type of single-peak pattern, whereas that of the relay intercropping treatments showed a type of double-peak pattern. Appropriately, limited single irrigation and controlled soil water content level could result in higher total yield, water use efficiency, and leaf area index, and improved yield components in relay intercropping. This practice saved the amount of water used for irrigation and also increased the yield. Therefore, heading stage of wheat and heading and anthesis stage of maize were suggested to be the optimum limited single irrigation time for relay-intercropped wheat and maize in the semi-arid area.

Effect of Different Lower Irrigation Limits on Rape Quality

In this study, two rape varieties, ＂Zajiaolvbang＂ and ＂bilv＂, were used as experimental materials to investigate the effect of different lower irrigation limits （80%, 60%, 40% and 20% of field capacity） on quality of pet-grown rape. The results showed that contents of soluble sugar, soluble protein, vitamin C, nitrate and organic acids in rape all increased with the decreasing lower irrigation limit. Rape plants represented the best quality with lower irrigation limit of 60% of field capacity.

Photosynthetic characteristics of intercropped winter wheat under limited supplemental irrigation in the semiarid northwestern China

A field experiment was conducted for intercropped winter wheat （Triticum aestivum） in 2002/2003 to evaluate the effects of limited supplemental irrigation on photosynthetic characteristics of intercropped winter wheat in semiarid environment. The result indicated that significances occurred in grain yield between the intercropped wheat treatments and sole wheat control （CKW）, and in yield between the irrigated intercropped wheat plots （WC2W, WC3W, WC5W） and not irrigated （WC1W） except for WC4W plots with nearly the same yield as WC1W. In comparison with CKW, 11.8%, 18.5%, 23.6%, 11.5%, and 30.7% of yield increase in the intercropped wheat plots were obtained in WCIW, WC2W, WC3W, WC4W, and WC5W respectively. Compared to the intercropped wheat plots without irrigation, yields in WC2W, WC3W, and WC5W were improved by 5.9%, 10.5%, and 16.9%, respectively. The dynamics of CGR and NAR in both intercropped （WC1W-WC5W） and solely cropped wheat （CKW） showed a type of ＂single peak＂ curves, with both the maximum CGR and NAR occurred during jointing to heading （14/4-6/5） of wheat. In addition, soil water potential （SWP） fluctuated as a function of the precipitation and limited supplemental irrigation.

Developmental Tendency of Dry Land Farming Technologies

The developmental tendency of dry land farming technologies in the semiarid area of China were reviewed based on the overview of recent progress in dry land farming researches from China and oversea. It was emphasized that conservation tillage, limited irrigation, genetic modification and chemical control are the important aspects for the dry land farming research and development of the future. In addition, some consid-