Effects Of Combined Application Of Organic And Inorganic Fertilizers On Apple Yield And Quality And Soil Phosphorus Distribution Under Grassy Mulching Condition

Shaanxi Province has become the first major apple producing province in China,due to its natural advantages such as moderate rainfall,superior light and heat conditions,large temperature difference between day and night,and sufficient sunlight.The Weibei dry plateau area is an important part of the Loess Plateau in northwest China,and the unique climate and soil conditions in this region are particularly favorable to the development of high-quality fruit industry.However,as phosphorus fertilizer is prone to chemical fixation in calcareous soil,it is difficult to be effectively absorbed and utilized by fruit trees,resulting in low yield and poor quality of fruit trees,reducing the commercial value of apples and limiting the sustainable development of dryland orchards.In order to reduce phosphorus fixation and improve phosphorus fertilizer utilization,this study relied on a 13-year long-term localization experiment,with the main treatment of grass mulching and clear plowing between rows and the secondary treatment of four fertilizer treatments,specifically no fertilizer（CK）,organic fertilizer（M）,nitrogen,phosphorus and potassium（NPK）,and organic inorganic fertilizer（MNPK）,to investigate the effects of organic inorganic fertilizer with grass mulching on soil phosphorus distribution and effectiveness in dryland apple orchards.The study investigated the effects of organic and inorganic fertilizer application on the distribution and effectiveness of soil phosphorus in dryland apple orchards under grass cover,and provided theoretical basis and technical support for the sustainable development of dryland orchards.The main findings of the study are as follows:1.The combination of grass mulching and organic and inorganic fertilizer can increase the fruit weight,fruit set and yield per unit area of fruit trees.The two-year data showed that the yield per unit area of fruit trees increased by an average of 9.77%in two years compared to clear-cutting.Fertilizer treatments（M,NPK,MNPK）under grass mulching significantly increased apple fruit weight and fruit set per plant compared with no fertilizer（CK）,thus increasing orchard yield per plant and yield per unit area,with the most significant effect of organic and inorganic fertilizer application.The yield per unit area and fruit weight of MNPK treatment were higher than those of MNPK treatment in clear-cut mode.2.The combination of grass mulching and organic and inorganic fertilizers increased the contents of soluble solids,soluble sugars and Vc,reduced the content of titratable acid and improved the sugar-acid ratio.Fruit soluble solids,soluble sugars,sugar-acid ratio and Vc content were the highest in MNPK treatment under grass mulching,with an average annual increase of 2.25%,2.61%,2.01%and 5.52%,respectively,compared with clear-cutting.It indicates that the combination of grass mulching between orchard rows and organic and inorganic fertilizer application can effectively improve the yield of fruit trees and increase the content of soluble solids,soluble sugars,sugar-acid ratio and Vc,which is conducive to the improvement of quality,yield and efficiency of apples in dryland orchards.3.The content of soil organic matter,effective phosphorus,total nitrogen and fast-acting potassium in 0-40 cm soil layer could be increased by grass mulching in 2020-2021 compared with clear tillage,and the content of soil organic matter,effective phosphorus,total nitrogen and fast-acting potassium in 0-20 cm and 20-40 cm soil layer under grass mulching and clear tillage with organic fertilizer application（MNPK,M）were significantly higher than that in treatments without organic fertilizer application（CK,NPK,NPK）.Soil organic matter,effective phosphorus,total nitrogen,and fast-acting potassium contents were highest in MNPK treatment under either grass cover or clear-cutting conditions.The two-year results showed that the two-year average contents of soil organic matter,effective phosphorus,total nitrogen,and fast-acting potassium in the MNPK treatment under 0-20 cm and 20-40 cm soil layers of grass cover increased by 0.5%and 5.2%;4.4%and 18.8%;7.7%and 11.3%;and 12.1%and3.8%,respectively,compared with those in the MNPK treatment under clear-cut tillage.4.Grass mulching had no significant effect on total N and P in leaves and fruits,but reduced total K in leaves and fruits.The MNPK treatment had the highest leaf total N,P,and K contents under raw grass mulching and clear-cut conditions.The average annual increase of leaf total N and fruit total N and K in MNPK treatment of raw grass mulching was 4.9%,1.6%and 3.8%,respectively,which could effectively promote nutrient uptake by fruit trees.5.The phosphorus form of 0-20 cm and 20-40 cm soil layers was dominated by hydrochloric acid state phosphorus（D.HCL-P）and residual state phosphorus（Residual-P）,and the proportion of water-soluble phosphorus（H₂O-P）and sodium bicarbonate inorganic phosphorus（Na HCO₃-Pi）effective phosphorus sources was low;the correlation coefficient between H₂O-P and effective phosphorus,total phosphorus,and phosphorus activation coefficient was the largest,and its biological effectiveness was the highest.It was the most effective phosphorus source.Organic matter,total nitrogen and fast-acting potassium showed highly significant positive correlations with effective phosphorus and phosphorus activation coefficient in 0-20 cm and 20-40 cm soil layers.D.HCL-P had the highest correlation with fruit total phosphorus and leaf total phosphorus,and was the main source of fruit and leaf phosphorus,and the highest correlation between leaf total phosphorus and fruit total phosphorus,indicating that phosphorus transport and migration occurred mainly between leaves and fruits.6.The ratio of inorganic P in 0-20 cm and 20-40 cm soil layer increased from 68.5%and66.1%to 75.8%and 69.7%,respectively,after grass mulching and different fertilization treatments.The proportion of residual phosphorus decreased from 26.8%and 27.0%to 18.3%and 23.5%.Combined application of organic and inorganic fertilizers could significantly increase the contents of available P,total P and phosphorus components in soil and the proportion of H₂O-P and Na HCO₃-Pi active P in soil.The range of increase of phosphorus form content and the proportion of inorganic P in soil under grass condition were better than that under clear tillage condition.