水氮耦合对固定道垄作栽培春小麦根长密度和产量的影响

固定道垄作(PRB)是在农田中设固定的机械行走道的一种垄作和沟灌栽培模式,是河西灌区春小麦取代传统平作和大水漫灌种植方式的一种新技术。为了明确PRB种植模式下合理的施氮水平和灌水量,2014—2015年连续2年采用二因素裂区设计,以3种灌溉定额(1200、2400和3600 m3 hm–2)为主区,以4种施氮水平(0、90、180和270kg hm–2)为副区,研究水氮耦合对小麦不同生育期的根长密度及最终产量的影响。随灌水量和施氮量的增加,根长密度呈现先增后降的变化趋势,且灌水量的效应大于施氮水平的效应;开花、灌浆和成熟期的根长密度与籽粒产量呈正相关。回归分析显示,根长密度最大值的水氮耦合条件是灌水量约2850 m3 hm–2、施氮量196~207 kg hm–2。中等灌水量(2400 m3 hm–2)条件下,小麦主要生育期根长密度显著增加,提高了根长密度在40~80 cm土层的分配比例,增加了水分利用效率和氮肥农学利用效率。综合评价小麦籽粒产量、水分利用率和氮肥农学利用效率,中等灌水量与中氮水平(180 kg hm–2)是所有处理中的最佳水氮耦合模式,可用于河西灌区春小麦PRB栽培模式。当加大灌水至3600m3 hm–2时,产量没有显著增加,水分利用效率和氮肥农学利用效率显著下降,其原因可能是高灌水量使小麦主要生育期的根长密度降低,且根长密度在0~40 cm土层的比例升高,在40~80 cm土层的比例下降。

Effects of Water and Nitrogen Coupling on Root Length Density and Yield of Spring Wheat in Permanent Raised-bed Cropping System

Permanent raised-bed (PRB) with fixed traffic lane and furrow irrigation is a new cropping pattern of spring wheat in Hexi Corridor of China, which may substitute the traditional flat-planting and flood irrigation technique in this area. To guild water and N application in spring wheat cultivation under PRB condition, we carried out a two-year (2014–2015) field experiment in a split-plot design, with irrigation as the main plot and nitrogen (N) application as the sub-plot. The irrigation amounts were 1200 (W1200), 2400 (W2400), and 3600 m³ ha^-1 (W3600), and the N application rates were 0 (N), 90 (N90), 180 (N180), and 270 kg ha^-1 (N270). The effects on wheat root length density (RLD) at different growth stages and final yield were assessed. With increasing the level of irrigation or N application, wheat RLD showed a up–down changing trend, and the irrigation effect was larger than the nitrogen effect. Grain yield was positively correlated with RLD at anthesis, filling and maturity stages. Regression analysis revealed that the highest RLD could be obtained under the combination of 2850 m³ ha^-1 irrigation and 196–207 kg ha^-1 N. In the moderate irrigation treatment (2400 m³ ha^-1), the RLD significantly increased at major wheat growth stages. Meanwhile, the RLD proportion in 40–80 cm soil depth raised, leading to increased water use efficient (WUE) and N agronomic efficiency (NUE_a) of wheat. The comprehensive consideration of wheat yield, NUE_a and WUE indicates that moderate irrigation (2400 m³ ha^-1) and N application rate (180 kg ha^-1) is the best management in PRB cropping wheat in Hexi Corridor. More irrigation to 3600 m³ ha^-1 had no significant effect to increase yield but resulted in significant decreases of WUE and NUE_a because wheat RLD at major growth stages was decreased under luxurious irrigation condition and the RLD proportion in 40–80 cm soil depth was low resulting from the increased RLD proportion in 0–40 cm soil depth.