Phosphrous aftereffects on soybean yield and nutrition status in wheat/maize/soybean intercropping system

In order to assess the aftereffects of phosphorus fertilizer (PF) which was applied in wheat growing season, a field experiment was done focusing on the phosphorus aftereffect on soybean yield and nutritionalstatus in the wheat/maize/soybean annual intercropping system. The results show that (Ⅰ) after the five phosphorus gradients (P2O5 0, 45, 90, 135, 180 kg/ha) on wheat, soilavailable phosphorus content (SAP) before soybean sowing are 19, 22, 51, 57 and 62 mg/kg respectively (mark as SP0, SP1, SP2, SP3, SP4 respectively). (Ⅱ) Soybean grain yields(SGY) are increased at first and then decreased with the increase of SAP, SGY of SP1 is highest (1797 kg/ha) and increases by 11.6% comparing to that of SP0, while SGY of SP2-SP4 are increased only by 4.3%-4.7% comparing to that of SP0, and there are no significant differences between SP1-SP4 four treatments; Soybean stem yield (SSY) increased withthe increasing of SAP, SSY of SP1-SP4 increased by 10.4%, 22.4%, 28.5%, 31.5% comparing to that of SP0, respectively. (Ⅲ)With the increase of SAP, soybean total pods number(TPN) and full pods number (FPN) increase. The largest TPN at SP4 increased by 11.1% to SP0 and the largest FPN at SP1 increased by 13.9% to SP0, while shriveled pods number(SPN) reduced significantly at first and then increased gradually with SAP increasing (the least at SP1 is 8.8 pods/plant, the largest at SP4 is 13.4 pods/plant). The ratio of FPN to SPN was the first significant increased and then gradually reduced (the largest at SP1 is 8.50, the least at SP0 is 5.06). (Ⅳ) Nitrogen and phosphorus content of soybean seeds or stems were reduced after the first increase trend with increasing of SAP, the maximum were at SP2 (Grain N 7.718%, P2O5 0.764%; stems N 0.659%, P2O5 0.065%), but their potassium content increases with the increase of SAP. (Ⅴ)There was a significant positive correlation between soybean stem biomass, phosphorus, potassium nutrient content, nitrogen, phosphorus, potassium nutrient accumulation and SAP. Soybean phosphorus uptaked at the SP2, SP3, SP4 treatments were 1.7, 1.6, 1.7 times but its biomass only 1.2, 1.3, 1.3 times of SP0, respectively. In summary, the suitability of soil phosphorus favor soybean growth, overvalue of SAP may cause soybean plants leggy thereby affect podding and seed. So in the wheat/maize/soybean annual intercropping system aftercrop soybean can be less or no application of PF and take full advantage of the phosphorus application for wheat, to improve the utilization efficiency of PF.