Effects of rotation model and period on wheat yield,
nutrient uptake and soil fertility in the Loess Plateau

【Objectives】Rotations of wheat-alfalfa, wheat-sainfoin and wheat-pea are common cropping systems in the Loess Plateau, northwest China. In this paper, the impacts of different cropping systems on the wheat yields, nutrient uptake and soil fertility were studied using a long-term experiment, in order to compare and recommend the optimum cropping system in this area.【Methods】 The long-term experiment was established in 1984. Eight treatments with triplicates were designed: continuous cropping of wheat(CK), three long-period rotations of wheat-alfalfa treatments: wheat→wheat→alfalfa→alfalfa→alfalfa→ alfalfa→potato→wheat (WAT1), wheat→alfalfa→alfalfa→alfalfa→alfalfa→potato→wheat→wheat (WAT2), and alfalfa→ alfalfa→alfalfa→alfalfa→potato→wheat→wheat→wheat (WAT3); two short-period rotations of wheat-sainfoin: wheat and sainfoin→sainfoin→wheat (WST1), sainfoin→wheat→wheat and sainfoin (WST2); two wheat-pea rotations: wheat and millet →pea→wheat (WPT1), pea→wheat→wheat and millet (WPT2). Plant and soil samples were collected after wheat harvest in June, 2004. Wheat yields, grain and straw nutrient contents and soil fertility were determined. 【Results】 The wheat grain yields in the rotation were 1.47% to 29.66% higher than the control, and the straw biomass were 2.17% to 29.77% higher. The increases were more obvious in wheat-alfalfa rotation and wheat-sainfoin rotation systems. The second year wheat cropping yields after alfalfa or sainfoin were higher than those in the first year, the rotation advantage became weaken in the third year. The long-period rotation of wheat-alfalfa favored absorption of N, K, Fe, Cu and Zn in wheat, and the order was WAT3 WAT2 WAT1. The short-period rotation of wheat-sainfoin favored absorption of N, K and Fe in wheat, and WST1 was slightly higher than WST2. The wheat-pea rotation favored absorption of N, K, Fe and Mn in wheat, and WPT2 WPT1. The rotation model and year after rotated crops affected more on the harvest indexes of microelements than on those of macro-nutrients. The wheat-pea rotation was conducive to the transfer of N, P and Cu to wheat grain. The wheat K harvest indexes of the three rotation systems were lower than those of the continuous cropping of wheat, and the Fe harvest indexes of the wheat-alfalfa rotation and wheat-sainfoin rotation were lower than those of the continuous cropping of wheat. Through rotation, soil total N was increased by 11.54%-20.51%, alkali-hydrolysable N increased by 9.66%-21.56%. The wheat-sainfoin rotation had obvious positive effect on soil organic matter, total N and available K, but negative on soil available P (decreased by 23.97%). The wheat-pea rotation showed obvious positive effect on soil P accumulation with a increase of 45.52% compared to control.【Conclusions】 The rotation mode of 2 to 4 years successive sainfoin→two years continuing wheat is proven to be the optimum rotation mode in the Loess Plateau, in case of attention be paid on increasing phosphate fertilizer application.