Abstract
Abstract: The research was carried out on 10° slope land of southern Ningxia during 2017-2018, and four different tillage measures, including conventional tillage (CK), furrow-ridge tillage (NH), furrow-ridge + straw mulching (SM) and furrow-ridge+plastic mulching (PM) were employed. The results showed that NH、SM and PM significantly increased the content of soil organic matter and available nitrogen compared with CK, increasing by 18.50% and 14.47%, 18.22% and 17.64%, 21.75% and 18.71%, respectively, however, there was no significant difference between the three tillage measures. The topsoil organic matter and available nitrogen of CK treatment increased from up slope to down slope showing the risk of losing from slope land. Whereas, NH, SM and PM exhibited the function of weakening the slope location effect, with the order of organic matter and available nitrogen from high to low: mid slope> down slope > up slope. Compared with CK, the soil available phosphorus and available potassium on slope land was decreased, where the soil available phosphorus under PM significantly was lower than others. The soil available phosphorus and available potassium showed low losing risk from slope land. The difference between tillages is mainly related to fertilizer input and crop absorption and utilization. NH, SM and PM significantly increased the crop yields, and the yield of maize and potato were increased by 27.03 % and 2.89%, 12.85% and 9.29%, 204.56% and 21.52%, respectively, showing significant slope location effect. From the perspective of slope distribution, as the slope position changes from up slope to down slope, corn yields gradually increased under NH, SM and PM. Potato yields of CK increased gradually with the slope position changes from up slope to down slope; Its NH and PM increased firstly and then decreased, with the highest yield on mid slope and the lowest on down slope; Its SM decreased firstly and then increased, with the highest yield on down slope and the lowest on mid slope. Two mulching tillage methods, SM and PM, significantly improved crop N, P fertilizer use efficiency, and in the first maize planting season they were increased by 7.92% and 16.83%, 217.03% and 241.59%, respectively, while in the second potato-planting season, they were increased by 89.43% and 44.62%, 97.31% and 49.66%, respectively. The variance analysis was performed on the soil nutrients and crop yields at different slope positions under different tillages in 2017 and 2018. From the perspective of soil organic matter and crop yield analysis, tillages and slope positions both showed extremely significant differences between 2017 (P＜0.01) and significant differences in 2018 (P＜0.05). From the perspective of available nitrogen analysis, tillages showed significant differences（F=1.88，P<0.05）in 2017 and extremely significant differences（F=117.71，P<0.01）in 2018，slope positions both showed extremely significant differences in 2017 and 2018（F=3.43 and F=19.60，P<0.01）. From the perspective of available phosphorus analysis, tillages showed significant differences（F=1.35，P<0.05）in 2017 and no significant difference （F=0.5，P>0.05） in 2018， slope positions showed extremely significant differences（F=6.74，P<0.01）in 2017 and significant differences （F=3.91，P<0.05）in 2018. From the perspective of available potassium analysis, tillages showed no significant difference（F=21.63，P>0.05）in 2017 and extremely significant differences（F=5.72，P<0.01）in 2018，slope positions showed significant differences（F=10.89，P<0.05）in 2017 and no significant differences（F=1.18，P>0.05）in 2018.Hence, it was believed that protective tillages focused on furrows and mulches can effectively block the nutrients lose, combat soil nutrients migration on slop farmland, and increase crop yield and fertilizer use efficiency.
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