Effects Of Phosphorus Application Rate,Combined Of Nitrogen And Phosphorus And Grass Planting On Phosphorus Forms In Soil And Phosphorus Utilization In Apples

Phosphorus is an essential nutrient for apple growth and development,and it is involved in biomolecule synthesis and material and energy conversion in plants.However,phosphorus interacts with soil in multiple ways（e.g.co-precipitation and adsorption）and is easily fixed by soil,thus changing the composition of soil phosphorus pool and reducing soil phosphorus effectiveness.Therefore,it is of great significance to explore effective measures to improve soil phosphorus availability for apple growth and development as well as efficient phosphorus utilization.In this study,we investigated the effects of phosphorus fertilizer reduction,combined application of nitrogen and phosphorus,and grass cultivation on apple growth and development and soil phosphorus morphological transformation through field and pot experiments,and the main results were as follows:1.Effects of different phosphorus application rates on apple yield,fruit quality and soil phosphorus:compared with farmers’customary phosphorus fertilizer dosage（P225 225kg/hm²）,phosphorus fertilizer reduction treatments of 20%～40%（P135 135 kg/hm²,P180180 kg/hm²）had no significant effect on the growth of new tip and leaves,but significantly improved fruit hardness,soluble solids,soluble sugar and sugar-acid ratio.After two consecutive years of phosphorus reduction treatment,the contents of Ca₂-P,Ca₈-P,Al-P,Fe-P,active organic phosphorus and medium active organic phosphorus in the soil were reduced to different degrees compared with the customary fertilizer application,with Ca₂-P and active organic phosphorus decreasing to a greater extent,but the phosphorus reduction Al-P,Fe-P,active organic phosphorus and medium active organic phosphorus contents in the 20%～40%treatment were not significantly different compared with the conventional phosphorus application treatment;phosphorus fertilizer reduction had less effect on Ca₁₀-P and medium stable organic phosphorus contents in the soil,and O-P and highly stable organic phosphorus were not significantly different among treatments.2.Effects of nitrogen and phosphorus fertilization on apple rootstock seedling growth,soil inorganic phosphorus forms and phosphorus utilization:The results showed that different N and P treatments significantly affected the biomass and root morphology of M9T337seedlings,and N2P2（N 300 mg/kg,P₂O₅200 mg/kg）treatment was the best,followed by N1P2（N 150 mg/kg,P₂O₅200 mg/kg）treatment.Plant phosphorus accumulation and phosphorus fertilizer utilization efficiency reached the maximum under N2P2 and N2P1（N300 mg/kg、P₂O₅100 mg/kg）treatments,respectively.Under the same P level,appropriate N increase can promote the absorption of phosphorus by seedlings and effectively improve the phosphorus fertilizer utilization efficiency of plants.High N（450 mg/kg）treatment（N3P1,N3P2）significantly inhibited the uptake of phosphorus by seedlings to soil,which was not conducive to the growth of rootstock seedlings.The soil available phosphorus（Olsen-P）content is mainly affected by the amount of P applied,and reaches a maximum of 27.86mg/kg under N2P2 treatment.The maximum alkaline phosphatase activity was 2.12 mg/（g·d）under N2P1 treatment.Compared with P alone,combined application of N and P increases the proportion of Ca₈-P and Al-P in the soil phosphorus pool that can be absorbed and utilized by plants,and reduces the proportion of Ca₁₀-P that is difficult for plants to absorb and utilize,and the proportion of Ca₂-P is also reduced;With the increase of N application rate,Ca₈-P and Al-P showed a trend of first increasing and then decreasing,and both reached the maximum under N2P2 treatment.Ca₁₀-P showed a gradually decreasing trend with the increase of N application rate.There is no obvious trend of Fe-P and O-P content under different N application rates.Reasonable N and P can improve the availability of soil phosphorus by changing the composition of soil inorganic phosphorus pools,and promote the growth of rootstock seedlings and the absorption of soil phosphorus.3.Effects of growing herbage on phosphorus uptake and soil phosphorus morphology of apple rootstock seedlings:Phosphorus reduction and growing herbage treatments significantly affected the root morphology of apple rootstock M9T337 seedlings,the best effect was 75%P+herbage treatment,followed by P+herbage treatment.Phosphorus accumulation in seedlings and phosphorus fertilizer utilization reached the maximum under P+herbage and75%P+herbage treatments,respectively.Compared with the conventional application of phosphorus,the phosphorus reduction treatment reduced the effective phosphorus content of the inter-root soil,while the herbage treatment increased the effective phosphorus content of the inter-root soil.Both phosphorus reduction and herbage treatments increased the inter-rooted soil alkaline phosphatase activity.Soil inorganic phosphorus fractions showed Ca₁₀-P>O-P>Ca₈-P>Al-P>Fe-P>Ca₂-P.Phosphorus reduction decreased the content of inorganic phosphorus fraction in the soil;growing herbage treatment increased the content of Ca₈-P,Al-P and Fe-P,decreased the content of Ca₁₀-P in the inter-rhizosphere soil,and had no significant effect on the content of O-P.Among the soil organic phosphorus fractions,phosphorus reduction and herbage both reduced inter-rooted soil active,medium active and medium stable organic phosphorus content compared with conventional phosphorus application,and the most significant reduction was observed under 75% P+ herbage treatment.