Abstract:

Partial rootzone irrigation can reduce water consumption and enhance water use efficiency. Compared with conventional irrigation, partial irrigation may reduce total biomass production, but will bring no loss of economic yield and even improve the quality of grains. While considerable expertise of partial irrigation is being developed, very little work has been conducted to understand how the uptake of water are affected when part of the root system is consistently or alternately exposed to watering and drying during their growing season. The present study was aimed to study the functions of different rootzones in water uptake under localized irrigation on maize grown in split-root containers. Maize was irrigated in both halves of the pot (control, C) or water was continuously supplied to the one-half of the pot and the other half kept dry (fixed partial rootzone irrigation treatment, F), or water was alternatively supplied to two halves of the pot for 10 days each (alternative partial rootzone irrigation treatment, A). These treatments lasted forty days in total and were divided into four treatment periods. For all three treatments, the amount of water consumption by maize, soil-root hydraulic conductivity from the whole rootzone and two half rootzones, and the soil water content from different rootzones were measured at fifth and tenth days during each treatment period. The hydraulic conductivity in soil-root system was measured using the pressure chamber. The results were as follows. For all treatments, water consumption by maize was significantly linearly correlated with soil-root hydraulic conductivity from the whole rootzone or irrigated rootzone, suggesting that crop water consumption can be represented by soil-root hydraulic conductivity from both the whole and irrigated rootzones. For the control, the percentage of hydraulic conductivity from one half rootzone was about 50% of that from the whole rootzone. For F treatment, the percentage of the irrigated rootzone was markedly higher than that of the non-irrigated rootzone and nearly reached 100%. As for A treatment, the percentage of two half rootzones alternatively changed, and the percentage of the irrigated rootzone always surpassed that of the non-irrigated rootzone. The percentage of the non-irrigated rootzone of A was much higher than that of F treatment. These indicated that for conventional irrigation, both two half rootzones contribute to water uptake by crops, while for F irrigation, only the irrigated rootzone does, for A irrigation, mainly the irrigated rootzone does and also the non-irrigated rootzone does some. For all treatments, soil-root hydraulic conductivities from the whole rootzone and irrigated rootzone were both significantly linearly correlated with soil water content of the irrigated rootzone, and the slopes were different among them and among different irrigation methods. Comparative analysis of these slopes confirmed the function of different rootzones in crop water uptake under different irrigation methods. The variance of the slopes for F treatment also pointed out that the non-irrigated rootzone decreased the hydraulic conductivity in soil-root system from the whole rootzone under fixed partial rootzone irrigation.

Key words: Localized irrigation in root zone, Water consumption, Root zone, Hydraulic conductivity in soil-root system, Soil water content