Increase of fertilizer solution concentration and biomass mixing proportion can enhance water and nutrients distribution in wetted soils under moistube irrigation

Moistube irrigation is a new water-saving technology for continuous underground irrigation that can provide an effective carrier for agricultural fertigation technology. In order to investigate the mode of distribution of water and nutrients in wetted soils in moistube fertigation in vertical insert mode under different proportions of biomass mixture of soil, a series of indoor soil box infiltration simulation experiments were carried out using peanut shell power as mixed biomass. In the experiments, three fertilizer solution concentrations (F₀:pure water at 0 g·L^-1; F_L:low concentration at 0.2 g·L^-1; and F_H:high concentration at 0.4 g·L^-1) and four proportions of biomass mixture (B₀:no mixing at 0; B_L:low mixing at 1.5%; B_M:moderate mixing at 3.0%; and B_H:high mixing at 4.5%) were designed to study the distribution characteristics of soil water content, nitrate nitrogen, available phosphorus and available potassium in wetted soils under moistube fertigation in vertical insert mode. The results showed that the distribution areas of water and nutrients significantly expended after biomass mixture, but fertilizer solution concentration had no significant effect on the distribution areas of water and nutrients. Water and nutrients contents gradually decreased with increasing horizontal distance from moistube in wetted soils and the maximum water and nutrients contents occurred just next to the moistube. The distribution of soil water and nitrate nitrogen were more uniform, while available phosphorus and available potassium formed accumulation area within 0-10 cm in the horizontal distance from the moistube. Fertilizer solution concentration and mixing proportion of biomass significantly influenced the mean contents of water and nutrients in the wetted soils. Compared with F₀, mean soil water content and soil nutrients (nitrate nitrogen, available phosphorus and available potassium) contents increased with increasing fertilizer solution concentration respectively by 3.94%-14.09% and 124.92%-458.05%. Mean soil water content and soil nutrients contents increased with increasing proportion of biomass mixture respectively by 12.89%-33.32% and 28.37%-115.44%, compared with those of B₀. The distribution uniformity of soil water and nitrate nitrogen was higher, but that of available phosphorus and available potassium was lower in the wetted soils under moistube fertigation in vertical insert mode. The distribution uniformity coefficient of soil water and nitrate nitrogen increased with increasing fertilizer solution concentration and biomass mixing proportion, while that of available phosphorus and available potassium decreased in the wetted soils. The relationship between mean soil water and nutrients and horizontal distance from the moistube conformed to the fourth log-Logistic model in the wetted soils under moistube fertigation in vertical insert mode. In summary, mixing biomass with soil was improved water and nutrients movement in the wetted soils under moistube fertigation in vertical insert mode. Also increasing the concentration of fertilizer solution and proportion of soil biomass mixture significantly increased soil water and nutrients contents. This in turn increased the uniformity of soil water and nitrate nitrogen, and promoted the accumulation of available phosphorus and available potassium around moistube. The research results provided solid theoretical basis and practical reference for moistube fertigation technology.