Author(s)

Y. Yu, P. Li, H. Jin, K. Zhang

Abstract

Inappropriate irrigation often leads to agricultural water waste via surface runoff and drainage to the deep soil. In this paper an investigation was carried out to determine optimal irrigation rate and time for crops grown in a sandy loam soil using the Hydrus-1D model. The threshold of soil water content in the root zone for irrigation was assumed to be the soil water content at which a half of readily available water was depleted in the root zone. The simulations for soil water content in the profile immediately after irrigation and 24 h after irrigation were performed with various irrigation rate and time, ranging from 1 cm/h and 3 cm/h for 1 h to 3 h. The simulated results showed that no surface runoff was occurred for the sandy loam soil, even under the rate of 3 cm/h irrigated for 3 h. The soil wetting depth 24 h after irrigation increased with the irrigation amount in an approximately linear manner. For the irrigation rate of 1 cm/h, the wetting depth was about 14.6 cm immediately after 1 h irrigation, and increased to 27.2 cm 24 h afterwards, compared with 27.8 cm and 58.6 cm for the irrigation rate of 3 cm/h. For a given irrigation amount, the distribution of soil water content was identical 24 h after irrigation, regardless of the irrigation rate. Furthermore, considerable expansion of the wetted soil area for different irrigation rate was also simulated due to soil water re-distribution. The results from this study implied that: 1) the expansion of the wetted area induced by soil water re-distribution needed to be taken into consideration for irrigation planning; 2) the entire root zone for a wide range of crops could be wetted with a single irrigation event; and 3) there were choices in terms of irrigation rate and time to bring up soil water content in the root zone.

Keywords

Hydrus-1D, precision agriculture, agricultural water management, optimal irrigation