Effects Of Whole Field Mulching With Bunch Planting On Soil Hydrothermic Status,yield And Water Use Efficiency Of Spring Wheat In Semi-arid Area

Spring wheat(Triticum aestivum L.) is one of mainly grain crop in China, its rank after rice. The cropland of wheat had not fluctuated sharply, but the yield increased from 1949 up to now. Recently, the wheat planting decreased yearly,because the economic developing and agricultural technology innovation, the productivity of wheat is mostly depended on the per unit area yield. In Recent years,whole field soil-plastic mulching with bunch planting(PM) is applied widely in arid and semi-arid northwestern China because it can increase yield. However, there were no systemic investigations on the mechanism of yield increment in this technology. To understand this mechanism, take spring wheat as meterials, field trial were carried out in dingxi county of Gansu province during 2010-2011, where located at hilly and semiarid northwest Loess plateau. The three treatments of the trail were, 1) whole field soil-plastic mulching with bunch planting(PM), 2) gravel and sand mulching with flat planting(SM), and 3) flat planting without mulching(CK). Soil temperature,soil water storage in 0-200 cm, wheat growth index, yield, yield components and water use efficiency of wheat were determined and analyzed to explore the increasing mechanism of whole field soil-plastic mulching with bunch planting and their effect on soil water balance. The main results are as follows:1. PM and SM could improve 0-25 cm average temperature 1.8 ℃ and 1.4 ℃,respectively, before jointing stage, warming effect gradually weakened after jointing,disappeared form heading to flowering stage, reappeared at havest stage, PM and SM increased by 0.7 ℃ and 0.9 ℃respectively, compared with CK.2. Soil temperature coefficient of variation of PM and SM were less than air temperature during whole growth period, PM was smallest, SM was followed, CK was largest among there treatments. Meanwhile, soil temperature gradient was followed the sequence of PM <SM <CK at the point of highest soil temperature, the soil thermal conductivity in PM treatment was lower than SM and CK, at the point of lowest soil temperature, soil temperature gradient was PM> SM> CK, soil thermal conductivity of PM was stronger than SM and CK. Visible, mulching could respondto changes in soil temperature, then adjust the soil heat transfer properties, maintain stability of soil temperature, especially in the period of highest temperature, therefore reduce the stress of high temperature on wheat reproduction growth.3. Because mulching treatment could improve soil temperature before jointing stage of wheat and stabilize soil temperatures, PM and SM could ahead each growth period, prolonged reproductive growth stage, shortened the total growth period of wheat. Among three treatments, PM and SM shorten the total growth period by 7-10 days and 5-6 days, extended reproductive growth stages 2-4 days 2-3 days,respectively, compared with CK. A relatively long reproductive growth stages of wheat improved dry matter accumulation and transformation, lay the foundation for high yield.4. Compared with CK, PM and SM could improved siginificantly 0-40 cm soil moisture conditions, especially in drought years, meeted the early growth of wheat,meanwhile promoting water consumption in 0-200 cm after wheat emergence. Soil water consumption of PM was the largest in 60-80 cm, SM and CK was 40-60 cm during the first planting year; PM was maximum in 120-180 cm soil layer, SM and CK was 60-80 cm during the second years. After two years continuous cultivation,Water depth of PM extends from 120 cm to 200 cm, SM extends from 120 cm to 140 cm, CK Water depth unchanged. Leisure efficiency of PM was the largest, up to62.52%-96.45%, SM was 57.72%-87.10%, CK was 32.69%-71.73%, and the leisure efficiency of each treatment increased with the planting years.5. PM and SM improved soil temperature during early growth stage, promoted water consumption after emergence, and accelerated the using of deeply soil moisture.Therefore PM and SM could significantly improve ear length, productive ear per m2,kernel per ear, 1000-kernels weight, yield and WUE, PM and SM could increase yield by 48.77%-815.79% and 49.41%-702.24%, increase WUE by 41.82%-661.20% and36.14%-640.43%, respectively, compared with CK.In summary, PM and SM could significantly improve soil temperature before jointing, promoting wheat seedling development; PM and SM could respond to changes of soil thermal, stabilized and reduced strong fluctuations of soil temperature,particularly in the highest temperature periods, eased heat stress on wheat productive growth, therefore, growth period of PM and SM was in advance, reproductive growth stage was prolonged, the total growth period is shortened, laid the foundation for high yield; Meanwhile PM and SM could promoting soil water consumption in 0?200 cm soil layer after wheat emergence. Wheat yield and WUE increased insignificantly, but with the increasing of planting years, depth of water consumption deepened, leisure efficiency decreased, water balance keeping might be disadvantage through several years. In dry farming region in northwest, China, whole field soil-plastic mulching with bunch planting(PM) can receive the high wheat yield, but the negative impact of the technology can not be ignored. Therefore, the research on its negative impact should be strengthened and the reasonable solution should be given to ensure that the technology is not only high yield but also ecological security.