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Microhole subsoiling decreasing soil compaction, and improving yield and seed quality of cotton

Wang Huijie;Hao Jianping;Feng Ruiyun;Nan Yang;Yang Shuqiao;Nan Jianfu;Agronomy College, Shanxi Agricultural University;Cotton Research Institute, Shanxi Academy of Agricultural Sciences;Institute of Crop Sciences, Shanxi Academy of Agricultural Sciences;Institute of Agricultural Resource and Economy, Shanxi Academy of Agricultural Sciences;  
During long-term conventional tillage, frequent use of heavy farm machinery in field operations results in narrow soil effective(plow) layer and thick plow pan. The plow pan resulting from soil compaction is a key constraint on soil quality and crop growth in cultivated land. To address this problem, microhole subsoiling is an alternative to conventional tillage. By reducing the tillage area, microhole subsoiling breaks the plow pan and increases soil permeability, which facilitates root growth into deeper soil, improves uptake of water and nutrients by plant, and reduces surface soil structure damage. Presently, the effects of microhole subsoiling on soil environment, cotton growth and development, and seed quality traits are not well understood. A comparative study of microhole subsoiling and conventional tillage(control) was conducted by one-year field experiment on the Nanhua Farm in Yuncheng, Shanxi Province, China(April 2013 to May 2014). Microhole subsoiling was implemented by vertical drilling using a soil auger with the diameter of 8 cm. Vertical subsoiling was conducted to 80 cm depth in a hole-like pattern at specific intervals. In microhole-subsoiled plots, the actual tillage area was about 239.2 m2/hm2, i.e., only 2.39 % of total area. At the seedling stage, soil compaction remained almost unchanged and less than 558.8 k Pa at 0-40 cm depth in microhole-subsoiled plots, whereas that in control plots was significantly higher and up to 9 069.7 k Pa at 20 cm depth. At the boll opening stage, soil compaction increased slowly up to 1 174.2 kP a in microhole-subsoiled plots, while that in control plots reached a maximum of 8 089.7 kP a. Meanwhile, soil bulk density in microhole-subsoiled plots remained lower and decreased from 1.56 to 1.05 g/cm3 at 35-40 cm depth. Owing to the loosening of deeper soil, microhole subsoiling effectively induced cotton roots to go deeper. The main root reached the depth of over 80 cm depth in microhole-subsoiled plots and 70 cm depth in control plots. At the depth of below 30 cm, microhole subsoiling doubled root biomass(19.77% of total root biomass) and increased lateral roots(32.62% of total lateral root) compared with the control(9.81% of total root biomass and 19.42% of total lateral root). The 5-room boll rate was 15% higher and the number of seeds per cotton pulp was greater by from 1 to 2 in microhole-subsoiled plots than in control plots. At the second and fifth seed positions, cotton seed index, proportion and fiber length were significantly higher in the former than in the latter by 0.03 g, 0.035 g/cm3 and 2.25 mm, respectively. Similar trends were observed in the emergence and healthy seedling rates, i.e., 1.01% and 2.27% higher in microhole-subsoiled plots than in control plots, respectively. The mortality and weak seedling rates were 0.92% and 1.41% lower in the former than in the latter. Seed protein was significantly higher(P0.05) while seed fat content was significantly lower(P0.05) in microhole-subsoiled plots than in control plots. Additionally, the number of bolls per plant, boll weight and lint yield were 6.34%, 5.75% and 10.12% higher in microhole-subsoiled plots than in control plots, respectively. Benefit analysis showed that compared with the control, microhole subsoiling improved the net income of cotton cultivation by 3 338.00 yuan/hm2. This benefit was mainly due to cotton yield increased significantly, seed sowing rate reduced effectively and relatively less input of tillage cost. This study revealed that that microhole subsoiling could effectively break local plow pan, thus alleviating soil compaction and reducing soil bulk density. The improvements of soil environment would induce cotton roots to go deeper and increase the number of lateral roots, thus improving seed quality and cotton yield. Microhole subsoiling overcame the environmental problems caused by conventional tillage regarding high energy consumption and severe soil surface damage, and achieved the goal of improving land productivity. The results presented provide the experimental evidence for the application of microhole subsoiling in cotton production.
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