The effect of organic fertilizer on the changes of soil physical properties in different rotations cultivation in permanent plots

Introduction
Organic matter is one of the important indicators of soil quality. Organic matter increases water retention in the soil and helps to transport water and air in the soil. Organic matter increases crop growth and provides nutrients needed by plants and soil microorganisms. The amount of soil organic matter in nature depends on factors such as climate, soil properties, and agricultural management, especially in the plowing stage. This is although in many cultivated and undisturbed soils, the amount of soil organic matter reaches a constant value after some time and becomes balanced.On the other hand, most regions of Iran the arid and semi-arid and have low organic matter. The chemical composition of organic matter is approximately 50% of carbon, 5.0 % of nitrogen, 0.5% of phosphorus, 0.5% of sulfur, 39% of oxygen, and 5.0% of hydrogen, and these values change from one soil to another. The management of compost and plant waste is one of the most essential aspects of soil fertility management in the direction of sustainable agriculture. The research results showed that organic matter and carbohydrates are two factors related to the stability of soil structure. Considering the role and effect of using organic fertilizers (from animal sources and urban waste compost) on the physical characteristics of the soil, it is necessary to improve the productivity of soil and water, changes in the physical characteristics of the soil in different crop management (rotation) in fixed plots and in several years to be reviewed and evaluated consecutively.
 
Materials and Methods
This research has been done to investigate the effect of applying organic manure from animal sources and urban waste compost in different and conventional crop rotations in fixed plots and also to investigate the changes in the physical characteristics of the soil due to the application of the following treatments in Alborz Province (at the research station of the Soil and Water Research Institute, Karaj) was implemented from November 2016. After planting wheat in 2016 and harvesting it in 2017, the land alternated with fallow. Wheat was planted again in the fall of 1997 and corn was planted in July 1998. In the fall of 1998, wheat was planted again and then the land was alternated with fallow. This research was conducted in the form of randomized complete blocks in five treatments and three replications in plots with an area of 200 square meters. The treatments include 1- no planting (T1), 2- control without fertilizer use (T2), 3- application of nitrogen, phosphorus, and potassium chemical fertilizers based on soil test (T3), 4- annual application of 20 ton/h of animal manure (T4) and annual application 20 ton/h of compost (T5). By taking soil samples from the surface layer, the physical characteristics of the soil, including field capacity, permanent wilting point, bulk density, final infiltration of soil, and aggregate stability of soil were measured in different treatments. Soil physical characteristics were measured after harvesting each product from a depth of 0-30 cm in three replicates. By removing the soil surface layer, the aggregate stability was determined by the wet sieve method.
 
Results and Discussion
Treatments T1, T2, and T3 did not show significant changes in field capacity. The mean values of the field capacity of these treatments T1, T2, and T3 are about 17.8% and the treatment using animal manure (18.1%) and compost (18.3%) increases the field capacity by about 1.0 and 2.0 %, respectively, compared to the average treatments without the use of organic fertilizers. The values of bulk density changes in the treatments for the desired periods are not significant and it indicates that there is no specific trend in each period due to the changes in soil surface conditions for the treatments. The values of changes in the soil aggregate stability values have become significant only in the treatments of organic fertilizer consumption (from animal sources and compost) in the desired periods. The soil aggregate stability index in the treatment of using compost and manure increased by 27 and 18%, respectively, compared to the average of treatments without fertilizer use (1.1 mm), which indicates the role of organic fertilizer use in increasing the aggregate stability. The average final infiltration rate in the treatments without using fertilizer is about 28.1 mm h^-1 and the average rate of final infiltration in the treatments using manure and compost is about 32.7 and 33.3 mm h^-1, respectively. The average rate of final infiltration in the treatments using manure and compost has increased by about 16 and 19%, respectively, compared to the average of other treatments.
 
Conclusion
According to the obtained results and the changes in the physical characteristics of the soil affected by the use of manure and compost in the cultivation periods, the role of the use of these materials in improving the physical characteristics of the soil is generally evident. The average bulk density of treatments T1 to T5 was equal to 1.47, 1.52, 1.54, 1.54, and 1.54 g cm^-³, respectively, indicating a relative increase in bulk density in organic fertilizer treatments. The soil aggregate stability index in the treatment of using compost and manure increased by 27 and 18%, respectively, compared to the average of treatments without fertilizer use, which indicates the role of organic fertilizer use in increasing the aggregate stability. The average final infiltration rate in manure and compost treatments has increased by about 16 and 19%, respectively, compared to the average of other treatments, which indicates the effect of manure and compost application in increasing the final soil infiltration rate. Because for each crop rotation, the soil is subjected to tillage operations, therefore destruction of the surface layer of the soil (with more organic matter) and as a result intensifying the activity of microorganisms, from the effect of organic matter on the characteristics, the physical properties of the soil are reduced and it even causes that no special trend can be seen in the physical characteristics of the soil during the cultivation periods. Therefore, it is necessary to use a set of management strategies to improve the amount of organic matter or the physical characteristics of the soil.