Effects Of Soil Depth And Soil Tillage Method On The Sweet Potato’s Growth, Yield And Quality In Hilly Region

This test was the long-term conservation tillage location experiment, setting in the middle of Sichuan Basin hilly region by Sichuan Provincial Academy of Agricultural Sciences. It adopted two factors split-plot design, with soil depth as main plot factor and tillage method as deputy district factor. The influence of soil depth and tillage method on the sweet potato’s growth, yield and quality was studied in Sixth year. Main results showed that:1. Effects of soil depth and tillage methods on soil environmental factors. The treatment of100cm soil depth anniversary no-tillage with straw mulch (NTS) was the best to reduce soil bulk density, keep the soil moisture and adjust soil temperature.In the sweet potato growing process,0～30cm soil layer soil water content with100cm soil depth was the highest, compared with the treatment of40cm soil depth, increasing by0.01-0.07W%. The treatment of100cm soil depth was the best to adjust soil temperature and could decrease soil temperature in hot season(July24-August13), reducing at0.01～1.58℃,and improve soil temperature in cool season (September2-October12) increasing at0.16-1.43℃. In the0～20cm and20～40cm soil layers, the soil bulk density of100cm soil depth was the minimum.In the treatments of ridge sowing and crop rotation with straw mulch (RTS) and no-tillage with straw mulch (NTS), soil environmental factors was in compliance with trends. But in the treatment of traditional tillage (CK), the minimum of the soil bulk density was he treatment of40cm soil depth.In the three kinds of tillage methods, including traditional tillage (CK), ridge sowing and crop rotation with straw mulch (RTS) and no-tillage with straw mulch (NTS), compared with CK,NTS could decrease soil bulk density by1.31±1.97%and increase soil water content by4.00-25.00%. While RTS and NTS could be found in the high temperature period presented "cooling effect", low temperature period presented "warming effect", and NTS regulating soil temperature was the best..In the treatments of70cm and100cm soil depth, soil environmental factors was in compliance with trends.But in the treatment of40cm soil depth, the soil bulk density of CK was the minimum and soil water content of Ck was the maximum. This indicated that Straw mulch did not help to improve soil structural and increase soil water at the thin soil conditions. 2. Effects of soil depth and soil tillage method on physiological and biochemical characteristics of sweet potato. The treatment of100cm soil depth anniversary no-tillage with NTS was the best to change the physiological indexes.In the three kinds of soil thickness processing, compared with the treatment of40cm soil depth, the treatment of100cm soil depth could obviously improve the activity of the sweet potato’s root, dry matter accumulation, net photosynthetic rate, the activities of NR and INV, reduce the T/R ratio at the sweet potato growing process, and increase chlophyll content at mid-term and final phase of sweet potato roots enlargement.In the RTS and NTStreatments, each index was in compliance with rules. But in the CK treatment, the activity of the sweet potato’s root with40cm soil depth was the highest, consistent with the trend of soil bulk density.With potato growing process, compared with CK, NTS could significantly improve the activity of root, dry matter accumulation, and the activities of NR and NTS, enhance the net photosynthetic rate, effectively reduce the T/R ratio and promote Sweet photosynthetic products transfer to the underground part which was conducive to root enlargement, while it promoted the nitrogen metabolism and the sucrose conversion from sweet potato.In the treatments of70cm and100cm soil depth,each physiological indexeswas consistent with the above trend. But in the treatment of40cm soil depth, the CK treatment was beneficial to improve the activity of root and the net photosynthetic rate with full growth periods, reduce the T/R ratio and increase dry matter accumulation at mid-term and final phase of sweet potato roots enlargement. Because the CK with the treatment of40cm soil depth could be best to reduce soil bulk density, keep the soil moisture and improve the soil environment, and promote the development and enlargement of sweet potato roots.Increasing soil thickness and the NST treatment could promotes the growth and development of sweet potato, while interaction effects of soil depth and tillage method on sweet potato’s physiological indexes was obvious.3. Effects of soil depth and soil tillage method on the yield and quality of sweet potato.The treatment of100cm soil depth with NTS is the highest to the yield, soluble sugar content, starch content and crude protein content.In the three kinds of soil thickness processing, compared with the treatment of40cm soil depth, the treatment of100cm soil depth could significantly improve the yield by56.38-173.61%,than that of40cm soil depth. While the soluble sugar content, starch content and crude protein content were improved with the increase of soil thickness.These indexes of the treatment of100cm soil depth were the maximum, improved by10.08～72.11%,9.59～9.61%,12.01～22.43%than those of40cm soil depth.In the three kinds of tillage methods, the yields of RTS and NTS were significantly higher than CK, by27.13～29.94%,41.63～49.35%. The increase sequences of the soluble sugar content, starch content and crude protein content were the same, which were NTS> RTS>CK. In the treatments of70cm and100cm soil depth, yield and quality was consistent with the above trend. But in the treatment of40cm soil depth, the yields increase sequence were CK>NTS>RTS, with no significant difference and the crude protein content with RTS was the highest.This was because the CK treatment with40cm soil depth could help to improve the development and enlargement of sweet potato roots and promote the accumulation of photosynthetic products, thereby increasing the yield of sweet potato. In addition, RTS was beneficial to improve the activities of NR at prometaphase and final phase of sweet potato roots enlargement, promoting nitrogen metabolism and crude protein formation.In summary, in the40cm layer thicknesses, CK is the best farming methods; and in the70cm and100cm soil layer thicknesses, NTS is the best farming methods.100cm soil layer thicknesswith NTS was the most conducive to improve the soil environment, promote potato growth, improve yield and quality and the most suitable for high yield and quality tillage methods in hilly region.