The spread of fertility in the soil is often accompanied by the flow of soil moisture, that is, the more frequent the diffusion of soil moisture, the greater the change in fertility nutrients. The flow and diffusion of soil moisture can be measured, compared, and analyzed using a soil moisture meter. Today we use soil moisture meters to analyze the effect of water flow on nutrient fertility.
In this experiment, when the soil moisture content was 20%, it was equivalent to 68% of the field water holding capacity, slightly less than the capillary water fracture volume (70% to 90%). At this time, the moisture of the soil in the soil is broken and the ion diffusion rate is greatly reduced. The released nutrients cannot be removed in time and accumulate on the surface of the fertilizer particles. Therefore, the concentration of the external solution increases, and the osmotic potential ratio of the nearby local soil solution is calculated. The value is much higher, so that the actual release rate and maximum release rate are lower than those predicted from soil water potential. When the matric potential is 0.01 MPa, the diffusion rate of the soil solution is the limiting factor affecting the nutrient release rate.
In this experiment, the soil matric potential at a water content of 30% was 0.0094 MPa, and the release rate under this condition was consistent with the predicted value. Water content less than 20%, with the soil moisture content decreased, the measured release rate is much lower than the predicted value. At soil moisture content of 10% and matrix potential of 0.76 MPa, the release rate was consistent with the predicted values ​​at 20 days fertilization. With further release, the released solution accumulates around the particles due to a decrease in the vapor pressure difference between inside and outside, and the solution is not sufficiently diffused. Similarly, when the water content was 4.2%, the fertilizer solution was not sufficiently diffused from the start of the release, and the fertilizer particles were covered with the high-concentration soil solution, so that the difference between the internal and external water vapor pressures was significantly reduced.
In water-saturated soils, the diffusion coefficients of most of the monovalent and divalent cations in the soil are one to two orders of magnitude smaller than those in aqueous solutions, and the diffusion coefficient of soil ions varies with changes in soil moisture content. Surface moisture in the drylands varies from 8% to 40%. Based on the above results, we believe that the release of controlled-release fertilizers in dryland soils cannot be predicted by the model obtained under saturated water, and the effect of soil moisture on the nutrient release rate of controlled release fertilizers must be considered.
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