Mapping of field capacity and wilting coefficient in china for drought monitoring

Abstract

Water is held in the soil pores by weaker capillary forces. When a soil is sufficiently wet, its capillary forces can hold no more water and the soil is at field capacity. Field capacity reflects the water holding capacity of the soil. Most agricultural crops require irrigation through the dry season, harvest, and after harvest. Specific water needs can be very different from one crop to another and, for the same crop, depend on soil type and climate. Some crops benefit in the quality of fruit produced when the soil water content is regulated during a specific growth stage of the plant. Some crops are sensitive to too much water in the soil, while other crops are sensitive to minor fluctuations in soil water content in the root zone during the growing season. Before a crop’s water needs can be addressed, and a specific water management program can be established, several important plant and soil parameters need to be determined. Field capacity of the soil is one of the important parameters. As a soil begins to dry out, however, increasingly stronger forces hold the pore water until a point is reached when plants can no longer extract any water from the soil. This state of soil moisture is the wilting coefficient of a soil. The wilting coefficient for a crop in a particular soil means that the water in the soil can no longer be easily extracted by plant and the plant begins to wilt. The method of field capacity is douche of sample in the field usually. The sample in the field was saturated with water, and was allowed to gravity drain for a few days. Then you can obtain the soil water content in the balance of the soil water. This method is more fit to the real condition of the field, but not fit to the soil in which the osmosis is very bad. The method of wilting coefficient is biological method usually. The sample in the field was used to plant the crop in the lab until the crop begins to wilt because of the deficit of the water. The measurements of the two soil parameters are very complicated. coefficient because of many influencing factors, such as differences in soil texture, content of organic matter and the mode of the use of soil. Field capacity and wilting coefficient of a soil vary with each factor. Soil texture is a physical property of soil and is determined by the percentages of soil separates. Content of organic matter will affect the hole of soil and the arranging mode of soil grains. The mode of planting will affect the physical and chemic character of soil. Usually we think the two soil parameters are relative changeless year by year, they fluctuate from year to year in a specific range in fact. Because of complicated determine method of soil parameters and too much influencing factors, some scholars put forward models to calculate field capacity, but quantifying each factor is very difficult, so the model may be adaptive to a section. Researches usually use the observed data in the field. The observed data are not easily collected and not uniform, so the data researches used may be observed long before. Water in the soil between field capacity and wilting coefficient is the plant available water. Once you know the soil’s field capacity and wilting coefficient, you will know the soil’s total amount of plant available water. Soil water condition combined with the plant available water is used to master the law of variety in the soil water, and the intensity of transpiration and evaporation combined with the plant available water is used to analyze available water in the soil for some crop in different period of growth, then you can make irrigation schedule, regulated deficit irrigation, water conservation in agriculture. Drought could be reflected through monitoring the growth condition of the crop, while the growth condition of the crop rests with the soil available water. When the water extracted from soil can’t meet the requirement of the crop, the crop would be in the condition of drought and the growth would be affected. Knowing the two soil parameters, you can calculate the relative soil moisture through monitoring the real soil water, and analyze whether the soil water can meet the need of crop, then you can judge whether the drought for a crop could happen. Considering the need and broad application of the two soil parameters, mapping the countrywide field capacity and wilting coefficient are proposed.