Crop Yield And Soil Quality Of The Conversion Of Cropland From Medicago Sativa Grassland Compared To Conventional Cropland

Field experiment was carried out to further clarify the changes of soil quality and crop productivity to the conversion cropland from perennial M. sativa grassland in the semiarid area of China’s Loess Plateau in2010and2011. The field was grown for alfalfa for30-years, before it was converted to cropland. Four treatments were established in the experiment,1) MF:conversion cropland with fertilized;2) MO: conversion cropland without fertilized;3) NF:convention cropland with fertilized;4) NO:convention cropland without fertilized. The experiment was carried out at the Semiarid Ecosystem Research Station of Lanzhou University at Zhonglianchuan village, a northern mountainous region of Yuzhong county (36.05’N,104.42’E,2400m above sea level) in both2010and2011. Large (80cm) and small (40cm) ridges alternated and fully mulched with plastic was designed. Two rows of maize were planted on the ridge, and the distance between two rows was40cm.The results showed that the soil water content of conversion cropland in0-200cm soil depth had only78%of convention cropland in April2010, significantly lower than the convention cropland, after two growth seasons, in September2011, the soil water content of MO in0-200cm soil depth had reached to82.80%of NO, and the soil water content of MF in0-200cm soil depth had reached to89.78%of NF, and the soil water content in0-60cm soil depth of conversion cropland had more water restoration than those of convention cropland.0-60cm water content of MF and NF in April2010had82.5%of conventional cropland, after two growing seasons, the soil water content of MO in0-60cm soil depth had reached to101.12%of NO.In the0-100cm soil depth, TN content of four treatments decreased from September2010to September2011significantly. SOC content in the0-100cm soil depth of MF and MO were significantly decreased from September2010to September2011, but SOC content of NF and NO had no significantly changes. In September2010, SOC content of MF and MO in0-60cm soil depth was0.78%, higher than NF and NO, and reduced to0.68%and0.66%, respectively, in September2011, there was no significantly differences between NF and NO. But the SOC content of NF, NO, MF and MO in60-100cm soil depth changed from0.86%、0.88%、0.84%and0.76%in September2010to0.87%、0.91%、0.72%and0.66%in September2011, respectively.The yield of corn in the alfalfa fields after tillage was significantly lower than conventional farmland, accounting for about56.63-79.43%of its yield. The percentage of production of MO/NF increased from56.63%in2010to68.44%in2011, but MF/NF decreased from75.48%to67.86%.Conclusion:Soil water content had declined severely after M. sativa grassland was grown for30years, which induced the reduction of crop yield follow-up, but crop rotation could improve the soil water content, which was benefit for the sustainable development of farmland system.