| Crop root, an important organ for absorbing water and nutrients and synthesizing growth substances regulation, has a direct influence on crop growth and yield. Therefore, strengthening the study on the root is very important for the further improvement of the yield. Field experiments were conducted in 2005-2008 to study the effects of different conservation tillage systems, including conventional tillage (T), conventional tillage with stubble incorporating (TIS), no-tillage without stubble retention (NT), no-tillage with stubble standing (NTSS), no-tillage with stubble retention (NTS), on the soil environment, root development, and grain yield of winter wheat in Gansu Agricultural University Experiment Station, which can explain the mechanism of yield increase from root-soil system. The results showed that:1. No-tillage with stubble retention (NTS) significantly improved the root distribution in 0-10 cm soil layer, also improved that in 30-70 cm soil layer in Hexi Oasis Area. Under NTS treatment, the dry root weight, root length, and root surface area of 0-10 cm soil layer were 62.3-103.37 g/m2,3.43-5.47×103m/m2, and 5.06-8.02 m2/m2, compared to T treatment, significantly improved dry root weight by 27.78%-77.60%, root length by 30.18%-81.27%, and root surface area by 27.56%-97.18%, respectively; the corresponding data were 21.16-38.29 g/m2,1.17-2.15×103m/m2,1.76-3.00 m2/m2 for 30-70 cm soil layer, compared to T treatment, NTS treatments significantly improved dry root weight by 16.48%-36.87%, root length by 10.38%-40.47%, root surface area by 15.79%-39.13%, respectively. The root distribution in upper and deeper soil could effectively increase absorbing water and nutrients, which would be beneficial to form organs in early growing stage and delay root aging in later growing stage, and ultimately would establish the basis for improvement of the yield. The correlation showed that total dry root weight and total root length and yield were significantly positive correlations, and the correlation coefficients were 0.651 and 0.4481, respectively.2. The root distribution in 10-30 cm soil layer in T and TIS treatments were significantly higher than that in NT, NTSS and NTS treatments at winter wheat early growing stage (before flowering), but significantly less than that in no-tillage treatments (NT, NTSS,NTS) at winter wheat later growing stage (before flowering). At early growing stage (before flowering), the roots for T and TIS easily extended and penetrated to 10-to 30-cm soil depth because tillage operations loosened the soil, but the most of which were prevented to reach deeper soil by tillage pan (25 depth), and concentrated above them, however, the roots for no-tillage treatments mainly distributed in upper soil layer (0-10cm) because of enough water and nutrient, higher soil bulk density and strength, and the continuous cracks and biopores (old root channels) of the undisturbed soil were not destroyed by tillage practice, which made root penetrate to deeper soil. Therefore, the roots in 10-to 30-cm soil layer were significantly higher than no-tillage treatments. At later growing stage (after flowering), higher air temperature pricked up evaporation and transpiration, which significantly decreased soil water, and higher soil strength significantly restricted new root growth in T and TIS treatments, however, better soil water and temperature conditions which created by stubble mulch promoted new root growth and delayed old root death in no-tillage treatments. Therefore, the roots in 10-to 30-cm soil layer in no-tillage treatments were significantly higher than tilled treatments. The higher root distribution in upper soil at later growing stage in NTSS and NTS treatments effectively increased water and nutrient supply for shoot, prolonged shoot organization functional period, improved photosynthesis, which ultimately increased crop potential.3. No-tillage with stubble standing (NTSS) and no-tillage with stubble retention (NTS) significantly increased water content of fresh root in 0-20 mm soil layer. Higher water content of fresh root could increase root absorbing activity, decrease root MDA content and cell membrane permeability, and decrease membrane lipid oxidize and cell membrane structure hurts, delay root aging, decrease root death rate, prolong root functional period, ultimately would establish the basis for improvement of the yield.4. No-tillage with stubble standing (NTSS) and no-tillage with stubble retention (NTS) not only significantly increase soil water storage and significantly decreased soil temperature, but also significantly decreased soil bulk density and soil strength during later growing period. NTSS and NTS treatments significantly improved soil water storage in 0-30 mm soil layer by 1.92-11.65 mm and 1.55-13.52 mm compared to T treatment, 2.73-13.79 mm and 5.29-15.67 mm compared to TIS treatment, in 30-150 mm soil layer by 5.67-19.44 mm and 16.03-36.80 mm compared to T treatment,6.18-20.58 mm and 16.54-33.46 mm compared to TIS treatment. NTSS and NTS treatments significantly decreased the daily average soil temperature of 0-25 cm soil by 0.90-1.51℃and 0.91 1.32℃compared to T,0.50-1.20℃and 0.50-1.00℃compared to TIS, respectively. NTSS and NTS treatments significantly improved soil water content, which was beneficial to increase water content of fresh root, alleviate great changes of soil temperature, decrease the roots hurt by dry hot wind at later growing stage, delay root aging, and strengthen water supply for winter wheat at filling stage. Large root system could increase the soil porosity which could decrease soil bulk density and soil strength. However, the lower value soil bulk density and soil strength could improve the soil permeability, also benefit to root growing, which can result in root-soil system in good circulation. The correlation showed that total dry root weight and total root length and soil bulk density and soil strength were significantly positive correlations.5. No-tillage without stubble retention (NT), no-tillage with stubble standing (NTSS), and no-tillage with stubble retention (NTS) significantly improved organic matter, available P, and available N of upper soil, but went against to balance the organic matter and P of lower soil layer. Both before sowing and after harvesting, NT, NTSS and NTS treatments significantly improved organic matter and P of 0-10 mm soil layer than T and TIS treatment, but significantly decreased that of 20-30 mm soil layer than T and TIS treatment. However, available N of 0-30 mm soil layer under NT, NTSS and NTS treatments were significantly higher than that under T and TIS treatment. The correlation showed that total dry root weight and total root length and available N and P were significantly positive correlations.6. No-tillage with stubble standing (NTSS) and no-tillage with stubble retention (NTS) significantly improved, spikes per hectare, thousand-grain weight, and number of grain, and also significantly improved grain yield and water use efficiency. Compared to T treatment, NTSS and NTS treatments significantly improved spikes per hectare by 9.13%-19.14% and 13.56%-20.10%, thousand-grain weight by 2.82%-6.40% and 2.17%-10.13%, number of grain by 3.57%-23.41% and 10.34%-12.34%, yield by 6.98%-24.32% and 15.65%-30.59%, water use efficiency by 7.75%-26.81% and 17.15%-24.92%, respectively. 7. No-tillage with stubble standing (NTSS) and no-tillage with stubble retention (NTS) have optimized the function of root and shoot, and also effectively improved dry matter distribution between root and shoot, which can result in the root to shoot ratio in more balanced state. Under NTSS and NTS treatments, the rate of dry root accumulation were higher in early growing stage (before jointing) and were lower in later growing stage (after jointing) than T and TIS treatments, however, the rate of dry shoot accumulation were lower in early growing stage (before jointing) and were higher in later growing stage (after jointing) than T and TIS treatments. In NTSS and NTS treatments, the growing characteristic of root and shoot of winter wheat were beneficial to dry matter effective distribution between root and shoot, ultimately would establish the basis for improvement of the yield.
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