Effects of Plastic Cover Cultivation on Soil Microbial Biomass

Plastic covering is an efficient planting measure for rising production. It has been recently applied and extended widely in dryland farming areas of northwestern China. Especially, on the Loess Plateau, there are increasing areas of plastic cover. Plastic cover can change the soil temperature, moisture, air and sun light as well, and consequently influence the soil physical, chemical and biological properties. Soil microbe is a driver of material transaction and nutrient cycle in soil system. Soil microbial biomass carbon (C), nitrogen (N) and phosphorus (P) are recognized as a reservoir of soil active nutrients. At the same time, it is very sensitive to environmental factors, and thus can be served as one evaluation indicator of soil quality. The present study was conducted in field plots at Weibei dry area of the Loess Plateau to (1) investigate the changes and difference of soil microbial biomass (C, N, P) in the different growing stage of corn under different situations of fertility in plastic cover cultivation and no-cover lands; (2) monitor the influence of soil microbial biomass on the soil nutrient cycle in the plastic covering land; and (3) evaluate the effect of plastic cover cultivation on soil environmental factors.The field experimental research was conducted at Changwu Agro-ecological Experiment Station on Loess Plateau, Chinese Academy of Sciences. 30 field plots with each area of 32 m 2 (4×8 m 2) were employed. 18 plots were treated with plastic cover cultivation with 6 fertilizer treatments (1=N1P1, 2=N1P2, 3=N1P3, 4=N2P1, 5=N2P2 and 6=N2P3) (N1=112.5 kg/hm 2, N2=225 kg/hm 2, P1=75 kg/hm 2, P2=150 kg/hm 2, P3=225 kg/hm 2), and 12 plots were served as control plots (no-cover) also with 6 fertilizer treatments. Soil samples were taken in a depth of 0～20 cm in each growing stage. The chloroform fumigation-extraction method was used to test the microbial biomass (C, N, P). Results show that soil microbial biomass carbon under plastic cover cultivation were less than those of no-cover cultivation during seedling, heading and maturation stages in all the 6 treatments, but during jointing stage, it depended on the treatment. Biomass C in plastic cover land was higher than those in no-cover land with the fertilizer treatments of 2, 3 and 4, while it was less with fertilizer treatments of 1, 5 and 6. Biomass nitrogen has the same tendency as biomass carbon and it showed the most obvious at seedling stage, while it changed with different fertilizer treatments in jointing and heading stages. There was no big difference in maturation stage. At the corn jointing stage, soil microbial biomass phosphorus under plastic cover cultivation was less than that of no-cover cultivation, but at the corn heading stage, the former was higher than the later. This may be that the corn is sensitive to phosphorus. Because the jointing stage is the fastest growing period, in addition to the plastic covering with higher soil temperature, mineralization of phosphorus was speeding up with the increasing soil phosphorus activity.The t-test analyses of biomass C, N, P and soil moisture show that during whole corn growing process, soil microbial biomass carbon and phosphorus under plastic cover cultivation were less than those of no-cover cultivation. Soil microbial biomass phosphorus under plastic cover cultivation had different response to plastic cover cultivation in different growing stages. But it also had a negative effect on phosphorus in terms of whole growing periods. Therefore, the N-P rate in fertilizer and the amount of fertilizer using play a great role in soil microbial activity. Plastic cover cultivation for corn can greatly influence the soil microbial biomass C, N and P, and it plays different role in different growing stages.