Winter Wheat Yield And Resource Use Efficiency Under Conservation Tillage Affected By Water At Sowing, Nitrogen And Crop Management

Drought stress is the major limiting factor to increase wheat yield in the semiarid areas. Soil water at planting(SWP), nitrogen levels and crop management practices(root pruning or defoliation) could significantly influence wheat growth, water use efficiency(WUE) and nitrogen use efficiency(NUE). The objective of this study was to investigate effects of nitrogen levels, crop management practices(root pruning or defoliation) and SWP levels on population dynamics, water storage, grain yield, WUE and NUE under straw mulching in the rainfed area of Loess Plateau(2013.9-2014.7). The experiment involved three SWP levels(high, medium, low), i.e. irrigation 133 mm before sowing(W2), irrigation 66.7 mm(W1) before sowing and non- irrigation(W0), two nitrogen levels(low rate, 150 kg N/ha; high rate, 200 kg N/ha) and three types of population manipulation(root pruning(RP), defoliation(F) and untreated control(CK)), eighteen treatments in total. The main results obtained were as follows:1) When in-crop rainfall was 252 mm, the SWP levels(704 mm, 791 mm and 854 mm) had no significant effects on winter wheat population sizes from the seedling to wintering stages, while winter wheat population size increased with the increasing of SWP levels from the jointing to maturity stages in which significantly higher stems or ear numbers at high SWP level than at low SWP level. The SWP levels had no significant effects on winter wheat above-ground biomass(maturity stage) and grain yield. High and medium SWP levels significantly increased water consumption(ET) and decreased WUE compared with low SWP level. The SWP levels had no obvious effects on N partial factor productivity(PFPN), partial N balance(PNB) and N harvest index(NHI). But winter wheat total nitrogen uptake was greater than nitrogen application rate, and thus PNB values were less than one. The effect of different SWP levels on nitrate nitrogen content at top soil layers at wheat harvest was not obvious, but high SWP level could induce soil nitrate nitrogen movement to the deeper soil layers.2) Nitrogen rates had no significant effects on winter wheat population size under three SWP levels. However, low nitrogen rate was beneficial to increase stems or spikes under low SWP level and high nitrogen rate contributed to improve winter wheat stems or spikes under medium and high SWP levels at late growth stages. High nitrogen rate could improve winter wheat grain yield and above-ground biomass(maturity stage), but reduced winter wheat harvest index, slightly decreased water consumption and increased WUE under low SWP level. However, high nitrogen rate slightly decreased winter wheat grain yield and above-ground biomass, improved winter wheat harvest index, meanwhile, increased water consumption and decreased WUE under medium and high SWP levels. Low nitrogen rate could significantly improve winter wheat PFPN and PNB, slightly increased NHI under three SWP levels. Under high, medium and low SWP levels, the effect of nitrogen rates on water storage in 0-300 cm soil profile at wheat harvest was not markedly. Under tested year, there were no significant interaction effects of SWP levels and nitrogen rates on wheat grain yield, biomass, harvest index, yield components, ET, WUE, PFPN, PNB and NHI.3) Under three SWP levels,root pruning at re-green stage could improve winter wheat spikes’ proportion, defoliation at re-green stage slightly decreased population quantity at late growth stages. Root pruning significantly improved winter wheat grain yield and harvest index by increasing winter wheat ear numbers and thousand kernels weight under low SWP level and markedly raised winter wheat grain yield by increasing thousand kernels weight under medium and high SWP levels. Meanwhile, root pruning increased water storage in 0-300 cm soil profile at wheat harvest, reduced water consumption and increased WUE under medium and low SWP levels compared with defoliation and untreated control. In addition, root pruning raised winter wheat PFPN and NHI. However, defoliation at re-green stage reduced winter wheat grain yield by decreasing ear numbers and thousand kernels weight, meanwhile, decreased PFPN and NHI. Furthermore, there were significant interaction effects of SWP and crop management on winter wheat thousand kernels weight, but no significant interaction effects on ear numbers, kernels per ear, yield, biomass, harvest index, ET, WUE, PFPN, PNB and NHI.On the whole, in the wet year of Loess Plateau, the different SWP levels had no significant effects on winter wheat grain yield, above-ground biomass and NUE, but high and medium levels of SWP reduced winter wheat WUE. Nitrogen rates had no marked effects on winter wheat population size, grain yield and harvest index, but significantly affected winter wheat NUE. Root pruning at re-green stage could improve winter wheat grain yield, WUE and NUE. However, defoliation at re-green stage decreased winter wheat grain yield, WUE and NUE. Therefore, root pruning could be a viable practice to achieve high yield and high resource efficiency, while the interaction effects of SWP levels, nitrogen levels and crop management on wheat yield, WUE and NUE need further investigation in other weather conditions under conservation tillage.