Effects Of Different Rates Of Straw Mulch On Farmland Environment And Physiological Ecology Of Spring Maize (zea Mays L.) In Weibei Highland Area, China

Weibei Highland area is in the middle south of Loess Plateau,which is the major region of rain-fed agriculture of China. Less by natural rainfall and the impact of large inter-annual fluctuations, the long-term crop yields low and unstable, have seriously affected food security and agricultural sustainable development of the region. A field experiment (2007–2010) was conducted at the Heyang Dryland Farming Experimental Station in Shaanxi Province of China to determine the effects of straw mulch rates on farmland environment and physiological ecology of spring maize. Maize straw at rates of 0 (CK), 4 500, 9 000 and 13 500 kg/hm² were placed on field plots under growth periods and the whole growth periods (both growth and fallow period), respectively. The main conclusions of the study were as follows:1. Different rates of straw mulch to improve soil structure. Compared with CK, soil bulk density at 0 20cm soil layers of the whole growth period with straw mulch rates of 4500 (S1), 9000 (S2) and 13500 kg/hm² (S3) decreased by 0.76%, 2.29% and 3.05%, respectively, soil porosity increased by 0.18%, 1.67% and 2.32%. Dry sieving of soil aggregates indicated that the treatments of >0.25mm content of the soil aggregates in 0 10cm and 10 20cm soil layers of the treatments with straw mulch during the whole growth periods were higher than the control (CK), especially in S2 the highest, increased by 5.57% and 8.57%, respectively. Wet sieving of soil aggregates obtained show that >0.25mm water stable aggregate content in 0 10cm and 10 20cm soil layer of the treatments with straw mulch during the whole growth periods was less than the CK, but in the 30 40cm soil layer more than the CK. Trends in soil bulk density, soil porosity and aggregate under growth period was the same as the whole growth period, but the latter less than the former whole.2. Different rates of straw mulch significantly decreased the soil temperature at different soil layers. Soil temperature diurnal variation of S1, S2 and S3, soil temperature to a minimum at 8:00, the difference is also minimal; 14:00 noon to the highest temperature difference between the maximum; PM soil temperature after 18:00 noon. Compared with CK, 2 mean annual soil temperature of S1, S2 and S3 in 0-15cm soil layer decreased by 2.6, 3.2 and 3.9℃during seedling; 60d after sowing, respectively, and decreased by 2.2, 3.6, 4.2℃; difference gradually decreased 90d after sowing; soil temperature of the average growth period decreased 0.9, 1.6 and 1.9℃. After sowing maize 0-30d, 0—5cm layer of soil temperature treatments for 2 years (2009-2010), on average, compared with CK were significantly (P<0.05) lower 3.4, 4.4 and 4.8℃, which was followed at 10 cm soil layer, which of 15—25 cm of soil was no significant difference among treatments. Growth of straw mulch treatment S4 (4500), S5 (9000) and S6 (13500 kg/hm²) temporal variation of soil temperature and was consistent with the whole growth period.3. Different rates of straw mulch effectively control the soil moisture. Fallow at the end, soil moisture of the whole growth period on soil water effects, the best in the 2009-2010, 2008-2009, and 2007-2008, followed by the annual minimum. 3-year average soil water storage in 0—200cm soil layers of S1, S2 and S3,compared with CK,increased by 9.14, 20.71 and 26.04 mm, differences were significant (P<0.05). however,3-year average soil water storage in 0—200cm soil layers of the growth period with straw mulch was no significant difference,compared with CK.Different Rainfall years, the soil water storage in 0-60cm soil layers under the whole period and growth period, both showed that 0-60d after sowing a larger increase than CK, with the trend of shrinking over time. 4-year average soil water storage in 0-60cm soil layer of S1, S2 and S3, compared with CK increased 4.40, 8.45 (P <0.05) and 10.75 mm (P <0.05), which was the largest increase in 2010 (normal year), in 2008 (drought year), followed in 2009 (wet year) was the worst. 0—60cm soil water storage under the whole period and growth period change in the same trend, but overall the former higher than the latter, 4-year average soil water storage in 0-60cm soil layers of S4, S5 and S6 increased, respectively, 2.60, 6.17 and 8.78 mm .4. Different rates of straw mulch to improve soil nutrient content and soil enzyme activities. Among them, the whole growth period of treatment overall higher than the growth period covered by treatment. The average total nitrogen (TN) content in 0²0 cm soil layer of S4, S5 and S6 at the end of harvest stage increased by 9.01%, 17.12% and 19.82%, compared with CK, differences were significant (P <0.05); 3-year average total nitrogen (TN) content for S1, S2 and S3 increased by 17.12%, 25.23% and 21.62%, the difference also reached a significant level (P <0.05). TN concentration of S4, S5 and S6 showed a single peak in the whole growth period of volatility, peak after sowing 60d (compared with CK lag 30d), average TN concentration of the whole growth period, than in CK 0²0 cm soil increased by 7.32%, 9.76% and 9.76% in 2009. Invertase activity of S1, S2 and S3 in the whole growth period increased by 10.16%, 25.85% and 20.14% than that of CK, and increased by 4.63%, 16.58% and 10.52% of S4, S5 and S6. besides, S2, S3, S5 and S6 were significantly higher than CK, but the S2 and S3, S5 and S6 showed no significant difference; urease activity of the whole growth period and growth period with straw mulch showed a "N"-shaped curve during the entire growth stages. urease activity of the whole growth period of S1, S2 and S3 increased by 2.19%, 5.58% and 3.78% than that of CK, respectively, and S4, S5 and S6 increased by 0.40%, 2.39% and 1.39%; phosphatase activity of the whole growth period and growth period with straw mulch showed "M" shaped curve fluctuations, the peak after sowing, respectively 90d and 120d. phosphatase activity of S1, S2 and S3 in the whole growth period increased 6.35%, 13.76% and 11.11%, respectively, compared with CK, and S4, S5 and S6 increased by 4.23%, 11.51% and 8.86%, respectively; compared with CK, the catalase activity of S1, S2, S3, S4, S5 and S6 increased by 1.02% 2.65%, 2.35%, 0.94%, 1.93% and 1.78% during the whole period, respectively, with no significant difference in CK.5. Different rates of straw mulching enhanced the accumulation of soil organic matter, improve soil carbon fractions. 0-20cm soil layer, compared with CK, S1, S2 and S3 total organic carbon (TOC) content increased by 5.08%, 14.12% and 28.03% (P <0.05); active organic carbon (LOC) concentration was increased 19.20%, 44.02% and 23.50%, differences were significant (P <0.05); carbon management index (CMI) were higher than 20.94%, 46.86% and 50.21%, the difference also reached a significant level (P <0.05) . In addition, the spring maize yield with the LOC and the CMI were significantly (P<0.05) and significant correlation (P <0.01), but with no significant correlation between TOC.6. Different rates of straw mulch to improve the field microclimate, reducing spring maize difference between canopy temperature and air temperature (CATD), increased leaf water potential (LW), especially from 13:00 to 15:00 noon most obvious effect. S2 showed the best overall performance, its 14:00 and the average daily CATD, respectively -0.20℃and 0.79℃, respectively, compared with CK significantly (P <0.05) decreased 111.4% and 75.8%, and the 15:00 of the LWP to -1.58MPa, increased over 7.06% (P <0.05) than CK; the average CATD of S3 at 14:00 and lower than the S2, but there was no significant difference. In addition, canopy temperature, soil water storage of the whole growth period and growth period with straw mulch were significantly negatively correlated (P <0.05).7. Different rates of straw mulch delayed growth and development of spring maize. There were a more effect of two straw mulch methods on maize seedling, jointing and maturity influenced the growth and development, other growth stages was less affected. Compared with CK, 4- year results showed that S1, S2, S3, S4, S5 and S6, respectively, emergence delayed 4, 5, 7, 3, 4 and 7d, three leaf stage were delayed 0, 1, 3, 0, 1 and 3d, jointing were delayed 3, 3, 3, 1, 2 and 3d, mature stage were delayed 2, 4, 5, 0, 2 and 4d.8. Different rates of maize straw mulch increased spring maize photosynthesis, and enhance the potential activity of PSII. The net photosynthetic rate of CK and S1 in 2008 and 2009 was the "single peak" curve, the peak in the jointing stage; S2 and S3 for 2-year average was "double peak" curve, the peak at jointing and booting period, and the former higher than the latter. net photosynthetic rate (Pn), transpiration rate (Tr), stomatal conductance (Gs), leaf instantaneous water use efficiency (WUE instantaneous) of the different treatment with straw mulch increased significantly compared with CK, photosystem II (PS II) of the maximum photochemical quantum yield (Fv/Fm), PSII potential activity (F_v/F₀) and photochemical quenching coefficient (qP) also significantly increased compared with CK.9. Different rates of straw mulch to varying degrees increased maize grain yield. Among all the treatment under the whole growth period with straw mulch,with the highest yield of S2 and S3 (S2 and S3 was no significant difference), S1 the lowest. 3-year average grain yield of S1, S2 and S3 increase by 6.24%, 14.02% (P <0.05) and 14.46% (P <0.05), respectively, compared with CK, and increased by 1.76%, 9.42% (P <0.05) and 10.34% (P <0.05) for S4, S5 and S6, respectively. Biomass yield on the trend of consistent growth trend with grain yield, but the increase in the former less than the latter.Spring maize yield different values because of their characteristics are quite different. Yield components of three elements, each treatment with straw mulch the difference between kernel number per row and CK largest kernel weight followed, the number of rows ear smallest difference, indicating that differences in yield among different treatments was mainly due to different causes of rows per ear.10. Different rates of straw mulch to improve the spring maize water use efficiency (WUE). The largest increase in 2008 compared with CK, which was second in 2010, which was the lowest in 2009. 3-year average WUE of S1, S2 and S3 was increased by 1.08%, 6.45% and 5.38%, respectively, compared with CK, and 3-year average PUE increased by 13.07%, 21.59% and 21.59%; 4-year average WUE of S4, S5 and S6 was increased by 0.54%, 8.06% and 7.53%, and 4-year average PUE respectively increased by 2.27%, 10.23% and 11.36%. However, different rates of straw mulch treatment under the whole growth period and growth period with straw mulch was close to the water consumption coefficient.11. N prime accumulation in different organs of the treatment during whole growth period with straw mulch overall higher than the growth with straw mulch, and with the gradually increasing the rate of straw mulch increases (except grain N accumulation), the organs of the level of accumulation of N prime order: grain> ear leaf> stem and sheath> cob> husk. Different covering methods are covered by N efficiency factor, N fertilizer use efficiency and agronomic efficiency of N fertilizer of the treatment with 9000kg/hm² straw mulch was the best, Regardless of whether the whole growth period with straw mulch or growth period with straw mulch.12. The net benefit of each treatment are quite different in different years, to normal year (2011) the highest, dry years (2008) followed in, the wet year (2009) was lowest. 3-year the average net benefit increased by 6.61%, 18.87% and 17.39% for S1, S2 and S3, compared with CK; 3-year average cost ratio increased by 1.21%, 5.45% and 3.64%. The treatments of the whole growth period with straw mulch less than that of growth period with straw mulch.This study showed that the influence of different rates of straw mulch under whole growth period and growth period on soil moisture, soil temperature and soil nutrient, and spring maize yield, WUE, and water-saving benefits were significantly higher than CK, and the whole growth period with straw mulch were higher than the growth period with straw mulch, different rates of straw mulch treatment to the best overall performance S2. In view of this, Weibei Highland area and similar ecological zones for spring maize with straw mulch, the recommended way to select the whole growth period with straw mulch, and the rate of 9 000 kg/hm² with maize straw mulch could be preferable.