Effect of phosphate fertilizer on the improvement of yieldand nutrient use efficiency of soybean in wheat-soybean and wheat/maize/soybean systems

【Objectives】 The wheat/maize/soybean intercropping system has become the mainly farming mode in the hilly area of southwest China. Soybean, as the core of the intercropping system, should be researched on its higher yield and efficiency for the scientific management of the system. 【Methods】 A two-years’ field investigation was conducted in the long-term experiment of intercropping system for the comparison of the growth of soybean grown in the wheat/maize/soybean intercropping (IS) and rotation systems (SS). The biomass accumulation and grain yield, nutrient content and nutrient utilization efficiency in the harvest stage were measured in the two systems.【Results】 1)The dry matter accumulation rate (DMAR) of soybeans in IS was significantly lower than in SS before maize harvest, with respective value of 1.18 g/(m2·d) in IS and 1.52 g/(m2·d) in SS; the DMAR in IS became higher than in SS after maize harvest with value of 5.60 g/(m2·d) in IS and 4.15 g/(m2·d) in SS. 2) Soybean grain yield was affected by the soil available P contents. The highest yield was in treatment SP4 (in IS was 2923 kg/ha, in SS was 2400 kg/ha), which was significantly higher than in SP1 and SP5, but not significantly than in SP2 and SP3. The yield in IS was 20.3% higher than in SS. 3) The nitrogen, phosphorus and potassium contents in soybean grain in IS was higher than those in SS, those in stems and pods in IS were lower than in SS. The phosphorus and potassium contents in soybean plants were increased with the increase of soil available P, nitrogen contents was increased first and then decreased with the highest N contents in treatment SP4. 4) Nitrogen and potassium accumulation of the planting strip of wheat and soybean plants (WSPS) in IS were significantly higher than in SS, and decreased after the first increasing with the increase of soil available phosphorus. 5) Although the P fertilizer use efficiency (PUF) of WSPS gradually decreased with the increased soil available P contents, PUF of WSPS in IS were always higher than in SS in the same P inputs,as from P2 to P5 those in IS were 44.6%, 74.9%, 66.9% and 109.5% higher than in SS. 【Conclusions】 Compared with in wheat-soybean rotation, soybeen in wheat/maize/soybean intercropping shows yield and nutritional advantage. In the intercropping system, more nitrogen, phosphorus and potassium are transported from pods and stems to seeds,leading to higher yield and nutrient use efficiency.