Studies On Soil Water And Nitrogen Movement Under Negative Hydraulic Head Irrigation

Negative hydraulic head irrigation technology is a kind of water, fertilizer, energy-saving, active labor steady supply technology. This technology not only enables the crop to decide when to supply water and fertilizer, effectively solves the shortage of resources, environmental pollution and other issues, but also makes soil moisture and nutrient supplement steady, makes the crop grow under optimum moisture and nutrients status. This technology effectively solves the problem of low water and fertilizer use.This paper based on the indoor soil column experiment and greenhouse pot experiment, summarized the research about negative suction irrigation at home and abroad, combined soil column experiments and greenhouse experiments, studied the water and nitrate-n in soil under the under negative hydraulic head. On one hand, this negative pressure irrigation technology can guarantee the moisture in the soil. On the other hand, it can give negative pressure technology support and promote negative pressure technology. The results were as the follows:(1) Based on laboratory experiment data, studied the variations of cumulative infiltration volume, wetting front distance and infiltration rate versus time. Results showed that the cumulative infiltration volume with time can be expressed by power function. The cumulative infiltration volume with the square root of time can be expressed by linear relation. The cumulative infiltration volume with the wetting front distance can be expressed by linear relation. The wetting front distance with the square root of time can be expressed by linear relation. The infiltration rate with the reciprocal of wetting front distance can be expressed by linear relation.(2) Based on the One-dimensional water infiltration under negative hydraulic head, combined the different infiltration models, Results showed that there is a relationship between parameters of Philip infiltration formula and Kostiakov empirical formula. Philip infiltration formula, Kostiakov empirical formula and Green-Ampt infiltration formula can reflects the relationship between the fitted cumulative infiltration and measured cumulative infiltration. Compared the variations of cumulative infiltration volume and infiltration rate versus time under Philip infiltration formula, Kostiakov empirical formula and Green-Ampt infiltration formula, fitted cumulative infiltration volume and infiltration rate under Kostiakov empirical formula are closest to measured cumulative infiltration volume and infiltration rate. Kostiakov empirical formula can fit the cumulative infiltration volume and infiltration rate well under different negative hydraulic heads. Kostiakov empirical formula has good applicability under different negative hydraulic heads.(3) Based on greenhouse experiment data, results showed that nitrate-n content in soil is relatively stable versus time under different negative hydraulic heads, the same amount of fertilizer and fertilizing method. When fertilized in the bottom of the pot(B), nitrate-n content in the soil reduces in a slow steady rate, nitrate-n in the soil absorbs by crops. When continuous fertilized(C), nitrate-n content inthe soil remains unchanged or slightly increases at a slow rate. Compared the nitrate-n content in the soil under full fertilized(F) to the nitrate-n content in the soil under half fertilized(F/2), there is significant gap. With fertilization and irrigation process conducted, this gap gradually reduces. Under same negative hydraulic head, when full fertilized in the bottom of the pot(FB) or half fertilized in the bottom of the pot(F/2B), nitrate-n content in the soil reduces in a slow steady rate, nitrate-n content in the soil absorbs by crops. When continuous full fertilized(FC) or half fertilized(F/2C), nitrate-n content in the soil remains unchanged or slightly increases at a slow rate. With fertilization and irrigation process conducted, nitrate-n content in the soil is gradually closed. After a long process of fertilization and irrigation, nitrate-n content in the soil will become same. Based on the transport of nitrate-n content in the soil, we can know that nitrate-n content in the soil is stable and its distribution is uniform under different negative hydraulic heads.