Effect Of Replacing Nitrogen Fertilizer With Humic Acid Organic Fertilizer On Soil Nutrients And Apple Yield And Quality

The Loess Plateau region is a high-quality and major apple-producing area in China,and the efficient and sustainable development of the apple industry is crucial to the construction of the local ecological environment and the economic returns of farmers.However,over-fertilization of apple production in the region has long led to problems of declining soil quality and orchard ecological degradation,resulting in low economic and ecological benefits for orchards.A reasonable proportion of weight loss and organic fertilizer substitution is an effective way to improve orchard soil quality,and is a realistic way to achieve the goal of ’weight loss and efficiency’.In this study,fertilizer treatments of no N reduction + humic acid organic fertilizer replaces 20% and 40% of N fertilizer;fertilization treatments with 20% N reduction + humic acid organic fertilizer replaces 20% and 40% of N fertilizer were applied in apple orchards,and conventional fertilizer was used as the control treatment.By analyzing the changes in soil physical and chemical properties,leaf growth indexes and fruit quality indexes,we studied the changes in soil nutrients in the orchard under different fertilization treatments,and the influence on apple tree growth and development,fruit yield and quality,with a view to screening out the best ratio of organic fertilizers to replace nitrogen fertilizer and providing a theoretical basis for scientific fertilization of apple production in the Loess Plateau region.The main results are as follows.1.Effects of different fertilizer treatments on soil physical and chemical properties:Compared with conventional fertilizer(CK),reduced nitrogen fertilizer with humic acid organic fertilizer treatments all reduced soil p H and increased soil water content,organic matter,total nitrogen,nitrate nitrogen,ammonium nitrogen,fast-acting phosphorus and fast-acting potassium content.At the same level as nitrogen fertilizer,the content of organic matter,nitrogen,phosphorus and potassium in the soil increased significantly as the proportion of chemical fertilizer replaced by humic acid organic fertilizer increased.The S2treatment(no N reduction + humic acid organic fertilizer replaces 40% of N fertilizer)was the most effective in increasing the nitrogen content of the soil,while the S4 treatment(20%N reduction + humic acid organic fertilizer replaces 40% of N fertilizer)increased the soil organic matter content more in 0-20 cm,by 19.03%,14.62%,and 17.62%,respectively,compared with the conventional fertilization treatment(CK).Overall,the S4 treatment had the most significant effect.2.Effects of different fertilizer treatments on apple tree growth: Compared with conventional fertilizer(CK),the reduced nitrogen fertilizer with humic acid organic fertilizer treatments all increased chlorophyll content,leaf area and leaf weight,and leaf mineral content.At the same level of nitrogen fertilizer,the leaf area,leaf weight,chlorophyll content and mineral content increased significantly with the increase in the proportion of organic humic acid fertilizer replacing chemical fertilizer.The S4 treatment was the most effective in improving the content of nitrogen,phosphorus and potassium elements in the leaves,which increased by 8.41%,11.82% and 42.75%,respectively,compared with the conventional fertilizer(CK).3.Effect of different fertilizer treatments on fruit quality and yield: Compared to conventional fertilization(CK),reduced nitrogen fertilization with humic acid organic fertilization increased fruit yield and improved internal and external fruit quality.Fruit weight,hardness,soluble solids,VC content,and soluble protein content all increased with the increasing proportion of organic humic acid fertilizers replacing chemical fertilizers at the same level of nitrogen fertilization,while the titratable acid content decreased.At the same level of organic fertilizer,fruit quality also improved but was not significantly different as the rate of nitrogen reduction increased.Of all the fertilizer treatments,S4 was the most effective,with an increase in fruit weight,hardness,soluble solids,VC and soluble protein of5.99%,13.67%,6.35%,16.84% and 27.35% respectively compared to the conventional fertilizer treatments.Fruit yield was highest in the S2 treatment,with an 11.84% increase in yield compared to the conventionally applied fertilizer treatment(CK).In conclusion,the application of reduced nitrogen fertilizer with humic acid organic fertilizer can effectively enrich the soil,improve the mineral element content of leaves,fruit yield and optimize fruit quality.In production practice,it is recommended to use a fertilizer application rate of 20% N reduction + 40% replacement of N by humic acid organic fertilizer.