| The common fore-rotating crop model is long-term alfalfa planting in grass-grain crop rotations of Loess Plateau, which induces serious deficit of water in the deep soil and then damage sustainable ecosystem in the region. In order to solve these series of problems, a long-term rotation experiment has been established in Changwu county, Shanxi Province. The fore-rotating crop treatments were planting different legume forages in 9 years (2004/5-2013/4), pasture species were bush clover(Lespedeza davurica S.),milk vetch(Astragalus adsurgens Pall.)and alfalfa (Medicago sativa L.), which were planted in monoculture and mixture-bush clover (Bc), milk vetch (Mv), lucerne (L), bush clover+milk vetch (Bc+Mv), bush clover+lucerne (Bc+L), milk vetch+lucerne (Mv+L), three species composition (Three sc.) under three plant density(20, 80,320 plant per square meter), and also set fallow fields as comparison. Ryegrass(Lolium multiflorum Lam.)and winter wheat(Triticum aestivum L. cv.)as the subsequent crop were respectively planted in 2013/10～2014/6 and 2013/5-2013/9. The objectivities of this study were evaluating the effect of previous grass to subsequent crop in the soil moisture and fertility and crop yield, so as to get advatageous plant models.The soil water storage of 0-100cm after legume forages were affected by external factors, the average of soil water storage is 215.0mm before planting ryegrass (2013/4),242.5mm after harvesting ryegrass (2013/10) and 195.0mm after harvesting winter wheat (2014/7). Before ploughing, soil water storage of preceding treatments with alfalfa(alfalfa, bush clover+alfalfa, milk vetch+alfalfa, three species composition) in 100-500cm soil depth were significantly lower than other treatments(bush clover, milk vetch, bush clover+milk vetch). However, after ploughing and planting ryegrass and winter wheat, soil water storage of treatments with alfalfa have a higher net increment:the net increment of 100-200cm soil depth is -11.8mm and 200-500cm is 19.1mm, significantly higher than the other treatments(-36.1mm and -51.7mm). Soil water storage in 200-500cm after different legume forages is slowly to be the same.There were no differences in total organic carbon (7.52～9.05 g kg-1), total nitrogen (0.84～1.01 g kg-1) at the depth of 0-30 cm in the soil after planting ryegrass and winter wheat. However, total organic carbon was 5.01～6.64 g kg-1, which significantly increased 0.77～1.75 g kg-1 in the soil at depth of 30-100 cm compared to fore-rotating field, and the net increment of the total organic carbon after the three species composition is 1.75 g kg"1 on average, which is much higher than the others. Total nitrogen was 0.39～0.59 g kg-1 which significantly decreased 0.05～0.20 g kg-1 in the soil at depth of 30-100 cm compared to fore-rotating field, and the net increment of the total nitrogen after the three species composition decreased 0.05 g kg-1 on average, which is significantly lower than other treatments. Available phosphorous and total phosphorous content were not significantly changed due to a short-term of after-reap crop.Above-ground biomass and yield of wheat was significantly higher in the treatments including alfalfa compared to others. And the biomass and yield of wheat after the three species composition was 13503.3 kg hm"2 on average and 6976.4 kg hm-2, higher than most the other treatments.The effect of density treatment of fore-rotating crop was not significant on change of soil water storage, the change of soil organic carbon and total nitrogen and crop yield.Due to the results of this experiment, the three species composition (bush clover+milk vetch +alfalfa) was a advatageous plant model. |
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