Soil nutrient loss is an important issue for soil in recent years. Soil nutrient loss is affected by many factors. Soil nutrient testing instrument can help us accurately grasp these changes and provide help for soil nutrients and agricultural cultivation and fertilization.
1. Influence of soil initial water content and rainfall interval on runoff and soil nutrient loss
Smith (1972)'s expression of precipitation time for rainfall increases during the two periods of rainfall, the initial soil moisture content decreases, the water time is delayed, and the amount of runoff will be relatively reduced. On the contrary, before 2007-07-04 and 2007- 07-19, the weather was gloomy and often had light rain, and the initial soil moisture content was high (the surface soil water content was 25%-27%, compared to other rainfalls. 10% to 15% higher, runoff occurs at the beginning of rainfall, and therefore the total runoff is large.
According to the study of urban runoff pollution, with the increase of rainfall intervals, the accumulation time of pollutants on the surface increases, so the concentration of runoff pollutants increases, and the total amount of runoff pollutants also increases. However, the results of this study show that the impact of rainfall intervals on soil nutrient loss from cultivated land is not significant.
2. Effect of agricultural farming system on runoff nutrient loss The fertilization before rainfall will have obvious loss of soil nutrients.
From the end of June to the beginning of July of each year, it is the seedling stage of crops such as corn and soybeans, and requires a large amount of nitrogen nutrient substances. For example, before the rainfall in 2007-07-04, the farmland just applied a large amount of nitrogen fertilizer (such as urea and carbon ammonia) from the runoff. In terms of loss, there was a significant loss of nitrogen, and the loss of organic matter and phosphorus was not significant.
Soil disturbance before rainfall will increase the loss of soil particles and phosphorus. According to the survey, artificial soil disturbances existed before the two rainfalls of 2007-05-30 and 2007-07-19. Therefore, the loss of soil particles and total phosphorus is relatively high.
3, Correlation analysis of soil nutrient loss indicators
From the table, the correlation between total nitrogen loss and rainfall erosivity is poor, which is due to the process of topdressing nitrogen fertilizer during rainfall observation. Based on the analysis of the relationship between organic matter and total nitrogen and total phosphorus loss, the correlation between organic matter and total nitrogen is poor, and the correlation with total phosphorus is good. Therefore, the total nitrogen loss in cultivated land of floodplain may be inorganic mineral nitrogen. The main form, and the loss of total phosphorus may take the form of organic phosphorus.
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