| Plastic film mulching has been a common agricultural technique and cultivation practice since it was introduced to China in1978. However, the negative effects of long-term plastic film mulch are rather notable. The wide application of plastic film mulch technique over many years may form a visible series of mulch layers in soil hindering crop root development, pollute environment and damage the sustainability of agroecosystems by over-decomposition of organic matter, over-mineralization of organic nitrogen and over-consumption of soil nutrient. Hence, it is urgent to explore the process of soil nutrient transformation and accumulation under the mulching conditions, to provide guidance for rational utilization of plastic film mulching. Soil erosion has become the greatest threat to providing food for rapidly growing human populations. At the same time, non-point pollution has drawn worldwide attention since the1960s. Especially, agriculture induced soil erosion and non-point pollution is an environmental issue. But, the research about the effects of plastic film mulching on soil erosion and nutrient loss was less.Taking granite slope wash parent material developed brown soil in Yimeng Mountainous Area as experimental material, the objectives of this study were to quantitatively determine net N mineralization, mineral N leaching and peanut yield of different mulching seasons, using in situ soil core technique. The research contained five treatments:MO, non-mulched for the whole growing season; M1, mulching up to seedling stage from sowing; M2, mulching up to flowering stage from sowing; M3, mulching up to pod setting stage from sowing; M4, mulching for the whole growing season. Meanwhile, the experience of field runoff plots has the same plastic film mulching duration with in situ N mineralization experience, namely RMO, RM1, RM2, RM3and RM4. The objective of runoff plots study was to determine the effects of various plastic film mulching on soil and water loss. The major conclusions include:1. Plastic film mulching increased the soil temperature at the seedling stage and soil water content during the whole growing season. At the seedling stage, the average soil temperatures of the mulching and non-mulching treatment were27.1℃and25.1℃, respectively. Thus, mulching increased soil temperature and provided more optimum conditions for peanut sprout and growth at the seedling stage. As the plant canopy established, soil temperature in the mulching treatments had no obvious difference with the other treatments. Surface soil volumetric water content was higher with plastic mulching than without throughout the growing season except after heavy rainfall. When the plastic film removed, the soil water content was not significantly different with the non-mulching treatment.2. The effects of different plastic film mulching duration on soil net N mineralization were significant. Except for pod filling stage, plastic film non-removed mulching treatment has greater net N mineralization and net N mineralization rate compared with the non-mulched and film-removed mulching treatments. During the whole growing stage, the highest total N mineralization was139.7mg kg-1measured in the M4treatment; secondly, the total N mineralization of M3treatment was132.3mg kg-1; and the lowest value was32.3mg kg-1measured in the M1treatment; in the second place, the total N mineralization of MO treatment was45.1mg kg-1.3. Under the condition of our experience, plastic film mulching treatment significantly increased surface runoff and soil loss. The mean runoff from the RM4treatment was18.2%,20.9%,13.0%, and15.6%higher than that in the RMO, RM1, RM2, and RM3treatments, respectively. The mean runoff coefficient increased in the order of RMO, RM1, RM3, RM2and RM4at15.2%,15.2%,15.7%,16.0%and17.9%, respectively. The mean soil loss of nine rainfall events from the RM4treatment was8.2%,5.9%,6.8%, and6.5%higher than for the RMO, RM1, RM2, and RM3treatments, respectively.4. Plastic film mulching can significantly decrease N loss. In contrast to the results of soil and water loss, RM4treatment significantly decreased the N loss compared to the other treatments, with the average reductions being17.1%(12.6-26.6%) for NH4+-N,18.8%(14.5-23.3%) for NO3"-N,17.1%(13.1-21.6%) for DN,8.2%(1.0-11.6%) for PN, and13.2%(11.8-16.5%) for TN. The DN losses as proportions of the TN losses were much higher than the PN losses in all treatments. The proportions averaged54.1%(52.0-57.2%) for DN, and45.9%(42.8-48.0%) for PN losses. NO3--N was the main form of DN loss, accounting for31.1%-33.9%of the TN losses, whereas NH4+-N accounted for only11.4%-13.7%of TN losses.Various plastic film mulching duration has obviously influences on soil mineral N leaching. Due to the impermeability and endurance of plastic film, plastic film mulching protected the soil from direct infiltration of excessive precipitation, and so reduced the possibility of N leaching from the root zone. When the plastic film was removed, the N leaching increased notably due to the absence of mulching protection. In the process of experience, the M4and M3treatments had the lowest cumulative mineral N leaching and the leaching concentrations were14.0and14.3mg kg-1, respectively; cumulative mineral N leaching of MO treatment was15.7mg kg-1; Ml treatment had the highest cumulative mineral N leaching was16.3mg kg-1.5. From the effects of various plastic film mulching on soil N mineralization, soil and water loss and peanut yield, the optimum mulching duration on soil and water conservation and income can be obtained. In view of soil N mineralization and mineral N leaching, mulching for the whole growing season (M4) was beneficial to net N mineralization and mineral N accumulation, and can reduce mineral N leaching. As to soil and water loss, plastic film mulching increased soil and water loss, but decreased soil nutrient loss. Consider peanut yield, mulching for the whole growth season (M4) was not good to peanut growth. But mulching from sowing to pod setting stage (M3) can have the largest peanut yield. |
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