Effect of crops on rainfall redistribution processes under simulated rainfall

Abstract: Crop canopy greatly affects the distribution of rainfall or irrigation water in the canopy and topsoil, thus potentially causing uneven distribution of surface soil water content and altering water use efficiency. Rainfall and sprinkler irrigation water are partitioned into four components as it passes through the plant canopy: throughfall, stemflow, interception storage, and in-canopy evaporation. This study aimed to investigate the effect of crop canopy on the redistribution of rainfall. The simulated rainfall was used to measure soybean canopy stemflow and throughfall, and a spray method was used to observe canopy interception. In order to measure throughfall, stemflow, and interception storage at different times during the growing season of corn (Zea mays L.), soybean (Glycine max), millet (Setaria italic) and winter wheat (Triticum aestivum Linn.), the throughfall and stemflow were measured indoors during simulated rainfall events with different leaf area indexes (LAI) under different rainfall intensities, and the spray method was used to measure the interception storage of crop canopies with different LAI. The effects of LAI and rainfall intensity on throughfall, stemflow, and interception storage were analyzed. The results showed that crop canopy had a significant (p<0.05) effect on rainfall redistribution under simulated rainfall. For the four crops canopy under the rainfall intensity of 40 and 80 mm/h, throughfall accounted for 77.04% of the total rainfall, stemflow accounted for 24.07% of the total rainfall, and the canopy interception was quit small less than 1% of the total rainfall. Under corn canopy, throughfall accounted for 36.23% to 93.55% of the total rainfall with a weighted averaging 65.15% across the entire experiment; stemflow accounted for 5.98% to 70.42% of the total rainfall with a weighted averaging 34.59%; the average interception storage was 0.16 mm equivalent to 0.26% of the total rainfall amount. Throughfall under soybean canopy accounted for 75.32% to 97.08% of the total rainfall with a weighted averaging 85.52% across the entire experiment, stemflow accounted for 3.06% to 22.52% with a weighted averaging 13.58% across the entire experiment, and the average interception storage of soybean canopy was 0.48 mm equivalent to 0.90% of the total rainfall amount. For millet, throughfall ratio ranged from 66.18% to 91.97% with a weighted averaging 80.05% in whole growth season, stemflow ratio ranged from 6.30% to 32.80% with a weighted averaging 19.42% in whole millet growth season, and the interception storage averaged 0.28 mm equivalent to 0.53% of the total rainfall amount. Throughfall ratio under winter wheat canopy ranged from 76.40% to 81.85% with a weighted averaging of 72.18%, stemflow ratio ranged of 22.15% to 36.52% with a weighted averaging of 26.34%, and the interception storage averaged 0.88 mm equivalent to 1.5% of the total rainfall amount. The amount of throughfall declined gradually as the crops LAI increased, whereas stemflow and interception storage gradually increased. There was a positive correlation between rainfall intensity and throughfall amount and also between rainfall intensity and stemflow amount. The ratio of throughfall to the total rainfall was not significantly related to rainfall intensity (p>0.05). Similarly, the ratio of stemflow to the total rainfall was not significantly related to rainfall intensity (p>0.05). As the crop grew up, the spatial distribution of throughfall gradually became uneven and rainwater tended to concentrate in the inter-row area. This study provides important insights into the effect of the crop canopy on the redistribution of rainfall and this study can be used as a theoretical basis for effectively using agricultural water and for controlling soil erosion on slopes.