Effects of Different Tillage Measures on Root-Soil System of Winter Wheat in Hexi Oasis Area
根系是作物吸收水分、养分及合成多种生理活性物质的重要器官,根系的生长发育状况直接影响着作物生长与产量的形成。因此,加强根系研究,对作物产量的进一步提高具有重要的现实意义。本文于2005年9至2008年7月在武威黄羊镇甘肃农业大学教学试验农场通过田间定位试验系统研究了传统耕作(T)、秸杆翻压(TIS)、免耕不覆盖(NT)、免耕秸杆立茬(NTSS)、免耕秸杆覆盖(NTS)五种不同耕作措施对冬小麦根系时空分布、土壤环境及产量的影响,从“根土系统”角度阐述了保护性耕作条件下冬小麦产量变化的机理机制,得到以下主要结论：1.在河西绿洲灌区采用免耕秸杆覆盖(NTS)不仅显著促进了冬小麦根系在表层(0～10 cm)土壤的生长,使根系呈现“表聚”特征,而且也促进了根系在深层(30～70 cm)土壤的生长。NTS处理0～10 cm土层根干重、根长和根表面积分别为62.3～103.37g/m2、3.43～5.47×103m/m2和5.06～8.02 m2/m2,较传统耕作(T)分别显著提高27.78%～77.60%、30.18%～81.27%和27.56%～97.18%；30～70 cm土层根干重、根长和根表面积分别为21.16～38.29 g/m2、1.17～2.15×103m/m2和1.76～3.00 m2/m2,较传统耕作(T)分别显著提高16.48%～36.87%、10.38%～40.47%和15.79%～39.13%。免耕秸杆覆盖(NTS)促进根系在表层和深层土壤的分布,有效增大了对土壤水分和养分的吸收,有利于生长前期作物的器官建成和生长后期的延缓衰老,从而为作物产量的提高奠定了一定物质基础。相关分析表明,冬小麦产量与根干重和根长呈为正相关,其相关系数分别为0.651和0.4481。2.翻耕处理(T, TIS)促进了冬小麦生育前期(开花期前)根系在10～30cm土层的分布,而免耕处理(NT, NTSS, NTS)却在生育后期表现出明显优势。由于翻耕,冬小麦生育前期T和TIS处理耕层土壤疏松,易于冬小麦根系下扎,而坚硬犁底层(约25cm深)的存在阻止了大部分根系向下生长,使根系聚于犁底层之上。而生育前期免耕处理表层土壤水肥充足、容重和紧实度较大,使根系趋于表层(0～10cm)生长,同时,由于下层土壤扰动小,前茬作物根系穿插和土壤动物(蚯蚓等)活动留下的庞大土壤空隙未受破坏,消减了犁底层的阻碍作用,易于根系向下生长,从而使10～30cm土层根系分布小于翻压处理。冬小麦生育后期(开花期后),气温较高,土壤水分蒸腾和蒸发加剧,T和TIS处理上层土壤水分显著减小,根系死亡和腐解加大,同时,土壤紧实度显著增大,抑制了新生根系的生长,而免耕特别是NTSS和NTS处理由于秸秆覆盖,土壤水热条件易于根系继续生长和新生根系的产生,延缓了根系的衰老,从而使10～30cm土层根系分布大于翻压处理。NTSS和NTS处理根系在生育后期上层土壤分布的增大,有效增大了对冠部组织水肥的供应,延长了器官的功能期,增强其光合作用,从而为产量的提高增大潜力。3.免耕秸杆覆盖(NTS)和免耕秸杆立茬(NTSS)显著提高了上层(0～20 cm)土壤根系含水率。根系水分的提高有利于增大根系吸收活力,减小根系内MDA含量和细胞膜透性,从而减小膜脂过氧化水平,减小膜结构的损伤,延缓根系的衰老,降低根系死亡和腐解速率。与传统耕作(T)相比,NTS和NTSS处理分别显著降低0～10 cm土层根系干重衰减速率17.78%～41.69%和9.05%～44.70%,根长衰减速率15.00%～39.8%7和13.00%～43.79%,从而延长根系的功能期,为冬小麦产量的提高增大一定潜力。4.免耕结合秸秆覆盖(NTSS和NTS)具有较强的保墒作用和降温作用,而且也显著降低了作物生长后期的土壤容重和紧实度。NTSS和NTS处理较T处理分别提高0～30 cm土壤贮水量1.92～11.65mm和1.55～13.52mm,较TIS处理分别提高2.73～13.79mm和5.29～15.67mm；较T处理分别提高30～150 cm土壤贮水量5.67～19.44mm和16.03～36.80mm,较TIS处理分别提高6.18～20.58mm和16.54～33.46mm。同时,NTSS和NTS处理较T处理分别降低0～25 cm土层深度的日平均土壤温度0.90～1.51℃和0.91～1.32℃,较TIS处理分别降低0.50～1.20℃和0.50～1.00℃。NTSS和NTS处理不仅提高了上层土壤水分,而且也提高了深层土壤水分,从而为根系的生长奠定一定的水分基础。同时,土壤水分的增大又有利于提高根系含水率和缓解土壤温度的剧烈变化,从而减轻冬小麦生长后期高温特别是干热风对冬小麦根系的伤害,延缓根系衰老,增强其对冬小麦灌浆期的水分供应。冬小麦庞大根系的穿插增大了土壤孔隙度,从而降低了土壤容重和紧实度,而土壤容重和紧实度的减小又使土壤的通气透水能力得到提高,又有利于作物根系的生长,使根系与土壤处于良性循环。相关分析表明,土壤容重和紧实度与冬小麦根系干重和根长呈负相关。5.免耕(NT, NTSS和NTS)显著提高了表层土壤的有机质和速效磷,也显著提高了土壤的速效氮,增强了土壤的供氮能力,但不利于下层土壤的磷补充和碳平衡。无论播前还是收获后,NT、NTSS和NTS处理0～10 cm土层的有机质和速效磷都显著高于T和TIS处理,但在20～30 cm土层都显著低于T和TIS处理；而0～30 cm各土层碱解氮都高于T和TIS处理。相关分析表明,土壤速效氮和速效磷与冬小麦根干重和根长都呈显著正相关。6.免耕结合秸秆覆盖(NTS和NTSS)显著提高了冬小麦公顷穗数,千粒重和穗粒数,进而显著提高了产量,同时也显著提高了水分利用效率。与传统耕作(T)相比,NTSS和NTS处理分别提高冬小麦公顷穗数9.13%～19.14%和13.56～20.10%,分别提高千粒重2.82%～6.40%和2.17%～10.13%,分别提高穗粒数3.57%-23.41%和10.34%-12.34%,分别提高产量6.98%～24.32%和15.65%230.59%,分别提高水分利用效率7.75%2～46.81%和17.15%4.92%。7.在河西绿洲灌区采用免耕结合秸秆覆盖(NTS和NTSS)的耕作措施能够优化冬小麦根冠功能,增大干物质在根冠之间的有效分配,使根冠比处于较为经济的平衡状态。与传统耕作(T)相比,NTSS和NTS处理根系干物质积累速率前期(拔节前)大后期(拔节后)小,而地上干物质积累速率却前期(拔节前)小而后期(拔节后)大。NTSS和NTS处理这种根冠生长特点,优化了根冠功能,有利于干物质在根冠之间的有效分配,从而使其产量显著高于传统耕作。
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.