Abstract:
Abstract: Improving the uniformity of crop growth parameters and yield across the field is one of the objectives in utilizing the variable rate irrigation (VRI) technology. To improve the water management level of VRI, the crop growth parameters, including plant height, leaf area index (LAI), aboveground dry matter, leave relative chlorophyll content (SPAD), yield, and their spatial uniformity were compared between VRI and uniform rate irrigation (URI) managements, and the influences of soil available water holding capacity (AWC) on crop growth parameters and yield were also analyzed. This study was conducted at the experimental station of China Agricultural University in Zhuozhou, Hebei Province (39.45°N and 115.85°E) in 2014. This site belongs to the Taihang mountain alluvial flood plain and experiences a warm and semi-humid monsoon climate with an annual mean temperature of 11.6°C and an annual mean precipitation of 563.3 mm. One quadrant of the center-pivot controlled area (1.64 hm2) was used in the experiment. The main soil types were loam and sandy loam, and both the coefficients of variation for sand and clay percentiles increased with depth in the site. During the growing seasons of winter wheat and summer maize, the seasonal rainfall for winter wheat (61.2 mm) was substantially lower than the long-term average, while it (311.6 mm) was ample for summer maize. According to the relationships between field capacity, wilting point, and clay, silt, and sand percentiles measured from the upper 0.6 m of the profile, the experimental area was delineated into 4 management zones with AWC varying from 152.2 mm to 161.4 mm for zone 1, from 161.4 mm to 170.9 mm for zone 2, from 170.9 mm to 185.1 mm for zone 3, and from 185.1 to 204.7 mm for zone 4. Each zone was then equally divided into 2 sub-zones to represent the VRI and URI treatments. Each VRI treatment was individually managed with an equal irrigation trigger point of 0.45AWC. For the URI treatments, irrigation was triggered when soil water content in the management zone having minimum AWC values (zone 1) depleted to 0.45AWC. The soil water content was measured with Trime access tubes and Decagon soil moisture sensors. A center-pivot irrigation machine that had been modified to enable to apply variable rate in different plots was used to implement the experiments. The results indicated that the soil water content was different among management zones with different AWC values, and the difference increased during the growing season of winter wheat as the less rainfall than that for summer maize. Correspondently, the total irrigation amount was same for winter wheat between URI and VRI treatments, while it was 14.1% lower for summer maize than that for the URI treatment since the frequent precipitation decreased the dependence on irrigation. Compared with URI management, there was minor effect of VRI management on spatial uniformity of winter wheat and summer maize; the variation coefficient values for all parameters of winter wheat increased from 0.02 to 0.04, while it decreased by 0.05 and 0.02 for aboveground dry matter and yield of summer maize, respectively. No significant influences of VRI management on crop growth parameters and yield were detected, while their differences were significant among the management zones. The experimental results suggested that the management zones with different AWC should be managed individually with different irrigation trigger points to improve the uniformity of crop growth and to maximize the crop yield.