| A plastic-covered ridge and furrow rainfall harvesting (PRFRH) system is being promoted to increase water availability for crops for higher and stable agricultural production in arid areas. The technique which based on the collection and concentration of surface runoff from short slopes is especially useful in arid and semiarid regions where irrigation water is not available or too costly to use. In this system, the plastic-covered ridges served as a rainfall harvesting zone and furrows as a planting zone. The PRFRH system can make better utilization of light rain by harvesting rainwater through the plastic-covered ridge.Field experiments (using corn as an indicator crop ) were conducted in a rainfall-control chamber of the Crop Specimen Farm of the Northwest A&F University (108°04ˊE, 34°20ˊN) during 2006-2007. In order to investigate the mechanism of PRFRH on soil water and temperature effects of farmland, the experiment comprised the soil water content, topsoil temperature, physiological and ecological characteristics, and grain yield increase for planting corn in two patterns, namely, PRFRH and conventional flat practice (CK), by artificially simulated different rainfalls (230 mm, 340 mm and 440 mm). The main results showed as follows:1. Effects of PRFRH on soil water and temperature conditions in the topsoil under different rainfalls.1) The runoff efficiency (runoff/rainfall) of plastic-covered ridges was related to the rainfall intensity. The plastic-covered ridges had an average runoff efficiency of 95.1% as when the rainfall intensity was in the range of 30mm/h-40mm/h.2) The soil water content in plastic-covered ridges of PRFRH gradually increased with the time and accumulated rainfall increase during the corn growing period. At the rainfall of 230 mm, 340 mm and 440 mm, the amplitude for soil water content both in ridges and furrows increased with the rainfall increase.3) PRFRH had especially in clear day a significant effect on temperature increase in topsoil (0-20 cm). However, the topsoil temperature amplitude declined with the rainfall increase during crop growing period and soil layer depth. Within 60 days after planting, the average soil temperature at 10 cm in furrows for PRFRH during daylight increased 0.9-1°C,0.8-0.9°C and 0.7-0.8°C, respectively compared to flat practice when rainfalls were 230 mm, 340 mm and 440 mm during corn growth stages.2. Effects of PRFRH on physiological and ecological characteristics of corn under different rainfalls.1) At the rainfall of 230 mm and 340 mm, PRFRH increased the leaf instantaneous water use efficiency (WUE) by 30.0% and 22.1%, respectively compared to CK during the whole growth period of corn sown in summer.2) For corn sown in spring, at the rainfall of 230 mm, PRFRH increased the leaf instantaneous WUE by 13.6% compared to conventional flat practice during the whole growth period. At the rainfall of 340 mm, the leaf instantaneous WUE during jointing and flowering was increased by 15.2% and 30.1% respectively compared to control. The average leaf instantaneous WUE increased by 12.4% during the whole growing period.3) At the higher rainfall, the advantages of PRFRH on leaf net photosynthetic rate and WUE increment for corn sown both in summer and spring decreased compared to CK. At the rainfall of 440 mm or more, the leaf instantaneous WUE of corn even declined.3. Effects of PRFRH on corn growth and development under different rainfalls.1) At the rainfall of 230 mm-440 mm, the PRFRH planting could make developmental stages occur earlier. For corn sown in summer, the corn seedling emerged 1d in three rainfall levels. The jointing, flowering and maturing occurred earlier 8d, 5d and 11d, respectively at the rainfall of 230 mm, earlier 4d, 4d and 6d at 340 mm rainfall, and earlier 2d, 2d and 3d at 440 mm rainfall. For corn sown in spring, the corn seedling emerged 2d in three rainfall levels. The jointing, flowering and maturing occurred earlier 14d, 11d and 13d, respectively at the rainfall of 230 mm, earlier 10d, 9d and 8d at 340 mm rainfall, and earlier 2d, 2d and 5d at 440 mm rainfall. Effects of PRFRH on corn growth stages decreased with the rainfall increase. The order was as follows: 230 mm > 340 mm > 440 mm.2) PRFRH enhanced corn biomass accumulation at the rainfall of 230 mm-440 mm during the whole growth stages. Compared to CK, the dry matter weight under PRFRH after corn harvested, increased by 44.7%, 28.5% and 7.6%, respectively for corn sown in summer, and by 86.6%, 59.7% and 12.1%, respectively for corn sown in spring at three rainfall levels. 3) At 230 mm and 440 mm rainfalls, the grain yield of corn sown in summer under PRFRH increased by 1604kg·hm-2 (75.4%) and 1184 kg·hm-2 (36.7%), respectively compared to conventional flat planting. At the rainfall of 230 mm-440 mm, the grain yield of corn sown in spring under PRFRH increased by 2632 kg·hm-2(82.8%), 2347 kg·hm-2(43.4%) and 861 kg·hm-2(11.2%), respectively compared to control. The grain yield amplitude of PRFRH decreased with rainfall increase during corn growth stages. The PRFRH had no significant effect on yield increment especially at 440 mm rainfall for corn sown in summer.4) For corn sown in summer, PRFRH could enhance grain yield and WUE by 7.4 kg·hm-2·mm-1(73.3%) and 4.3 kg·hm-2·mm-1(40.2%) respectively compared to CK at 230 mm and 340 mm rainfall. For corn sown in spring, the grain yield under PRFRH increased by 11.3 kg·hm-2·mm-1(77.4%), 7.5 kg·hm-2·mm-1(43.1%) and 1.7(9.5%) respectively compared to control at the rainfall of 230 mm-440 mm.4. Effects of PRFRH practice on soil available nutrient under different rainfalls.1) At 230 mm, 340 mm and 440 mm rainfalls during the whole growing period of corn sown in summer, soil available nutrient contents (N, P and K) in topsoil were significantly increased due to the effect of harvesting water and nutrition in planting furrows of PRFRH, and the increment was responsible for rainfalls.2) At different rainfalls during the whole growth stages of corn sown in summer, the soil layer stations of soil available nutrient contents increase under PRFRH were different. When the rainfall was lower, the layer of soil available nutrient in farmland mainly focused on topsoil (0-40 cm). With the rainfall increase, the soil available nutrient contents in deep soil layer also enhanced.5. Effects of PRFRH on nutrient use efficiency (NUE) in farmland under different rainfalls.1) At the rainfall of 230 mm-340 mm, the PRFRH could increase NUE in farmland. For corn sown in summer, at 230 mm rainfall N NUE, P NUE and K NUE (NUEN, NUEP and NUEK) under PRFRH increased by 56.0%, 44.4% and 106.8%, respectively, at 340 mm rainfall, by 22.8%,18.1% and 35.5%, and at 440 mm rainfall there was no significant difference compared to conventional flat planting. For corn sown in spring, the NUEN, NUEP and NUEK under PRFRH increased by 64.0%, 52.2% and 123.9%, respectively at 230 mm rainfall, by 30.4%,21.8% and 41.2% at 340 mm, at 440 mm, the NUEN increased by 10.1% compared to CK, while NUEP and NUEK had no significant difference between two planting patterns.
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