Abstract: 【Objective】In drylands of northwestern China, we have a serious problem in winter wheat production such as huge amount of and widely distributed low-yielding fields and remarkable yield variations among land parcels of farmers, therefore, it is of great importance to explore the key factors affecting the yield for the purpose of closing the yield variations and increasing the average yield levels of winter wheat universally.【Method】A survey on 180 farmers’ fertilizer application in winter wheat production with the collection and analysis of their 0-100 cm deep soil samples in the corresponding fields was carried out in Shanxi, Shaanxi and Gansu provinces, the typical dryland wheat producing areas of the Loess Plateau in Northwest China, to study the relationship between the dryland wheat yield variations and cultivation, fertilization, as well as the main soil fertility factors.【Result】Observed winter wheat yields in the three provinces were in the ranges of 2 529-8 419, 1 344-8 073 and 2 984-7 145 kg·hm^-2, respectively. Compared with traditional cultivation, the wheat yield under plastic film mulching cultivation increased by 9.4%. Under traditional cultivation, the average yield of the high-yielding farmer group was respectively 37.5% and 77.2% higher than that of the middle- and low-yielding groups, and the corresponding average yield differences were 25.4% and 66.2% under plastic film mulching cultivation. For fertilizer application, under traditional cultivation the average nitrogen (N) rate in the high-yielding group was respectively 44.4% and 74.4% higher than that in the middle- and low-yielding groups, and it was also 9.9% and 13.5% higher in the high-yielding group than that in the middle- and low-yielding groups under plastic film mulching cultivation. Average phosphorus (P) rate in the high-yielding group was 31.1% higher than the average rate of the middle- and low-yielding groups under traditional cultivation, and it was correspondingly 35.4% higher under plastic film mulching cultivation. Under traditional cultivation the average potassium (K) rate in the high-yielding group was 62.1% lower than that of the low-yielding group, but it was 96% higher in the high-yielding group than that of the low-yielding group under plastic film mulching cultivation. For soil fertility factors, no significant difference was observed in the organic matter content in 0-100 cm soil layers among yield levels in traditional cultivation, but it was 20.8% higher in 0-20 cm soil layers of the high-yielding group than that in low-yielding group under plastic film mulching cultivation. Significant differences were found in the soil total nitrogen in 40-80 cm depth under traditional cultivation, of which that in 40-60 cm soil depth was 7.5% and 18.6% higher in the high-yielding group than in the middle- and low-yielding groups, and under plastic film mulching cultivation, total N was significantly different in 0-60 cm soil layers, of which that in 0-20 cm soil layers was 3.2% and 14.2% higher in the high-yielding group than in the middle- and low-yielding groups, respectively. The mineral nitrogen showed no significant difference among yield groups under traditional cultivation, but that in 80-100 cm soil layers of the high-yielding group was 1.6 times higher than that of the low-yielding group under plastic film mulching cultivation. The available P in 0-40 cm soil layers was significantly different among yield groups in traditional cultivation, and that in the high-yielding group was 74.3% and 86.9% higher than that in the middle- and low-yielding group, respectively, but no significant difference was found in the available soil P under plastic film mulching cultivation. Under traditional cultivation, the available soil K in the high-yielding group was 37.5% and 77.2% higher than that in the middle- and low-yielding groups, respectively, and that was not significantly different among yield levels under plastic film mulching cultivation. Soil pH showed no significant difference at different yield levels and among cultivations.【Conclusion】Main causes for yield variation were found to be the differences in cultivation, fertilizer application rates, and soil fertility factors as soil organic matter content and available P level. Therefore, in northwest drylands, keys to narrow the farmers’ winter wheat yield variations and increase its levels are to strengthen the management of soil water and employ water retention cultivations, reasonably increase N and P fertilizer input, control K fertilizer use in the middle- and low-yielding fields under traditional cultivation, increase P and K fertilizer application apart from stabilization of N input in the middle- and low-yielding fields under plastic film mulching cultivation, strengthen organic fertilizer application to increases soil organic matter content, water holding capacity and nitrogen supply capacity, and meanwhile enhance soil available P supply capacity in the middle- and low-yielding fields especially under the traditional cultivation, in order to realize the purpose of promoting wheat growth and increasing their grain yield in drylands.

Key words: dryland, wheat, yield, NPK fertilizers, cultivation, nutrient