Technical Study On Improving Phosphorus Availability In Wheat Field Soil By Cultivating Methods And Nitrogen Application Rates

In order to explore the optimal tillage method and nitrogen application rate combination that can improve soil physical and chemical properties,enhance soil phosphorus availability,and promote crop high yield,this experiment was conducted on a long-term positioning experimental field（36°17’N,117°17’E）at Shandong Agricultural University Experimental Station from 2011 to 2022 during the wheat growth season from 2021 to 2022.Three tillage methods were set in this experiment,which were straw non-returning+rotating tillage（RT）,straw returning+rotating tillage（RS）,straw returning+two years rotating tillage and one year deep tillage（RS/DS）.At the same time,four nitrogen application levels(300 kg ha^-1,225kg ha^-1,165 kg ha^-1and 0 kg ha^-1)were set up for 12 treatments.The effects of tillage methods and nitrogen application rates on soil phosphorus morphology and winter wheat yield were studied.From the aspect of soil physical and chemical properties,the mechanism of straw returning combined with two-rotation and one-depth tillage combined with 225 kg ha^-1nitrogen fertilizer to promote the transformation of soil phosphorus form to available state and improve its availability was clarified.The main research results are as follows:1.Effects of tillage and nitrogen application on soil physical and chemical propertiesSoil bulk density of 0-10 cm,10-20 cm and 20-30 cm was decreased by straw returning and nitrogen application,and soil porosity was improved.Compared with non-returning soil,straw returning significantly increased soil p H value under nitrogen application and reduced soil acidification caused by nitrogen application,but its alleviating effect gradually decreased with the deepening of soil layer.Tillage has a significant effect on the soil bulk density and porosity of deep soil.RS/DS can significantly reduce the bulk density of 10-30 cm soil and improve the soil porosity.Straw returning significantly increased the contents of total nitrogen,organic carbon and available phosphorus in the three soil layers by 39.80%,27.71%and20.76%,41.11%,31.50%and 27.91%,23.78%,20.71%and 17.39%,respectively,compared with non-returning straw.The contents of total nitrogen,organic carbon and available phosphorus in soil were increased by increasing nitrogen application,and the increase of straw returning combined with nitrogen application was higher than that of nitrogen application alone.The nutrient content of straw rotation tillage was the highest in 0-10 cm soil layer.Straw returning combined with two-rotation and one-depth tillage significantly increased the contents of total nitrogen,organic carbon and available phosphorus in 10-30 cm soil layer.2.Effects of tillage and nitrogen application on soil phosphorus formThe phosphorus forms in the three soil layers were mainly HCl-P,accounting for more than 60%,while H₂O-P and Na HCO₃-P accounted for relatively little.Straw returning significantly increased the contents of H₂O-Pi,H₂O-Po,Na HCO₃-Pi,Na HCO₃-Po,Na OH-Po and HCl-Po in soil,and significantly decreased the contents of Na OH-Pi,HCl-Pi and Residual-P.The addition of nitrogen fertilizer had a great effect on the morphology of different phosphorus.With the increase of nitrogen application rate,the contents of H₂O-Pi,H₂O-Po,Na HCO₃-Pi,Na HCO₃-Po and Na OH-Po in soil were significantly increased,while the contents of Na OH-Pi,HCl-Pi,HCl-Po and Residual P were significantly decreased.Under straw returning condition,tillage measures can significantly affect the phosphorus form in10-30 cm soil.The contents of H₂O-Pi,H₂O-Po,Na HCO₃-Pi,Na HCO₃-Po and Na OH-Po of RS/DS treatment are higher than those of RS treatment,while the contents of HCl-Pi and Residual-P are lower than those of RS treatment.Tillage had no significant effect on HCl-Po.Straw returning increased the active P ratio in 0-10 cm,10-20 cm and 20-30 cm soil layers,and decreased the stable P ratio and residual P ratio in the three soil layers.Deepening soil layer would reduce the effect of straw returning on P form.With the increase of nitrogen application rate,the proportion of active P increased,and the proportion of stable P and residual P decreased.The effect of straw returning combined with N fertilizer on P transformation was greater than that of N fertilizer alone.Compared with rotary tillage,the two-rotation and one-depth method significantly increased the active P ratio and decreased the stable P and residual P ratio in deep soil.The phosphorus forms in the three soil layers were mainly HCl-P,accounting for 60%,while H₂O-P and Na HCO₃-P accounted for relatively little.Straw returning significantly increased the contents of H₂O-Pi,H₂O-Po,Na HCO₃-Pi,Na HCO₃-Po,Na OH-Po and HCl-Po in soil,and significantly decreased the contents of Na OH-Pi,HCl-Pi and Residual-P.The addition of nitrogen fertilizer had a great effect on the morphology of different phosphorus.With the increase of nitrogen application amount,the contents of H₂O-Pi,H₂O-Po,Na HCO₃-Pi,Na HCO₃-Po and Na OH-Po in soil were significantly increased,while the contents of Na OH-Pi,HCl-Pi,HCl-Po and Residual P were significantly decreased.Under straw returning condition,tillage measures can significantly affect the phosphorus form in 10-30 cm soil.The contents of H₂O-Pi,H₂O-Po,Na HCO₃-Pi,Na HCO₃-Po and Na OH-Po of RS/DS treatment are higher than those of RS treatment,while the contents of HCl-Pi and Residual-P are lower than those of RS treatment.Tillage had no significant effect on HCl-Po.Soil physical and chemical properties had great influence on soil P morphology.Soil total nitrogen,organic carbon and available P were positively correlated with higher active P,but negatively correlated with stable P and residual P.There was a significant negative correlation between soil p H and higher active phosphorus.Soil bulk density and porosity both have effects on soil P morphology.3.Effects of tillage methods and nitrogen application on winter wheat yieldStraw returning significantly increased the number of grains per ear and 1000-grain weight.Although the 1000-grain weight was reduced by nitrogen application,the number of ears and grains per ear were increased and the yield was eventually increased.Tillage and nitrogen application had significant effects on winter wheat yield,and the effects of different tillage methods on winter wheat yield were RS/DS>RS>RT;The winter wheat yield was significantly increased with the increase of nitrogen application rate,and the increase of nitrogen fertilizer level significantly increased the winter wheat yield under the condition of no returning field.Under returning condition,winter wheat yield increased significantly when nitrogen fertilizer was increased to 225 kg ha^-1,but no significant increase was found when nitrogen fertilizer was increased to 300 kg ha^-1.Under straw returning condition,the combination of two rotation and one depth with 225 kg ha^-1level had the best effect on the yield increase of winter wheat.