Font Size: a A A

Dynamics Of Three Perennial Grass Legumes Aboveground Biomass,Soil Water Depletion And Its Effect On Soil Organic Carbon,Total Nitrogen In The Loess Plateau Of China

Posted on:2013-03-04Degree:DoctorType:Dissertation
Country:ChinaCandidate:X K GuanFull Text:PDF
GTID:1223330395461275Subject:Ecology
Abstract/Summary:PDF Full Text Request
Perennial forage legumes play a significant role in crop/livestock mixed farming systems in the semi-arid region of the Loess Plateau China as a stock feed and source of nitrogen for subsequent crops. However, there is little evidence to evaluate the long-term productivity, soil water dynamics, water use efficiency and its effect on soil organic carbon and total nitrogen. Thus, lucerne (Medicago sativa L.), the dominant forage legumes species, and two locally adapted species, milk vetch (Astragalus adsurgens Pall.) and and bush clover (Lespedeza davurica S.) has been chosen to estimate their effect on soil water, organic cabon and total nitrogen from2004to2010in the Loess Plateau of China. The results listed as below:The7-year total forage yield of milk vetch was56t/ha and bush clover was42t/ha, significantly lower than lucerne at91t/ha. However, despite lower water use efficiencies (16and12kg/ha.mm for milk vetch and bush clover, respectively, compared to22kg/ha.mm in lucerne), the water use by the two locally-adapted perennial forages was3460mm and3450mm in milk vetch and bush clover, respectively, which was less than3600mm in lucerne. After7years, lucerne had extracted water in the top5m soil, whereas milk vetch still had some water available below3m and bush cover used water mainly from the top2m of soil profile. We conclude that while the locally-adapted forage legumes may not be as productive as lucerne as a source of fodder in a mixed cropping/livestock system, they use less water and may be preferable in drier regions.After7years growth of milk vetch, lucerne and bush clover, the profile soil organic carbon content was expressed as S shape. The soil organic carbon concentration in surface soil layer (0-30cm) was8-9g/kg, and it was5-6.3g/kg and6g/kg in60-100cm and100-150cm soil layer respectively, which was higher than that in30-60cm and150-200cm soil depth. The soil organic carbon stock was increased along with legumes stand age. There was a linear relationship existed between SOC storage and legumes growth period in each soil depth except60-100cm, from which we found that in lucerne field, soil organic carbon sequester rate was1.4Mg C ha-1yr-1in 100-200cm soil depth,0.7Mg C ha-1yr-1and0.5Mg C ha-1yr-1in60-100cm and0-30cm soil depth respectively. It was1.6Mg C ha-1yr-1in100-150cm soil depth,0.9Mg C ha-1yr-1in150-200cm soil depth and0.5Mg C ha-1yr-1in0-30cm and60-100cm soil depth of bush clover field. Soil organic carbon sequester rate in milk vetch field was0.9Mg C ha-1yr-1in100-150cm soil depth,0.7Mg C ha-1yr-1in150-200cm soil depth and0.5Mg C ha-1yr-1in60-100cm soil depth, while it was only0.1Mg C ha-1yr-1in0-30cm soil depth. Totally, soil organic carbon storage in200cm soil profile was significantly increased by legumes cultivation compared with bare land. Soil organic carbon sequeatration of lucerne was24.1Mg/ha in7years, which was higher than that in bush clover (19.9Mg/ha) and milk vetch (14.6Mg/ha). On average, it was4.2Mg C ha-1yr-1for lucerne,2.8Mg C ha-1yr-1and2.1Mg C ha-1yr-1for bush cloer and milk vetch respectively. Bare land mineralized soil organic carbon0.6Mg C ha-1yr-1in200cm soil profile.Soil total nitrogen srorage of150-200cm soil depth was declined in milk vetch’s former3years growth period and increased in later4years growth period, lucerne and bush clover fluctuated in the former6years and significantly increased in7year. Soil total nitrogen srorage of30-60cm and60-100cm soil depth was significanly decreased in the whole experimental period and it was fluctuated and remained at the same amount when compared with the initial value in0-30cm soil depth. The whole200cm profile soil total nitrogen storage was increased in lucerne and significantly decreased in milk vetch and bush clover after7years cultivation, wherase it was stand at the same level in bare land. In October2010, soil total nitrogen of lucerne was significantly higher than bare land, milk vetch and bush clover was significantly lower than bare land. When compared three legumes between each other, lucerne was significantly higher than milk vetch. Soil total nitrogen concentration in200cm profile was expressed as S shape. It was0.9-1.1g kg-1in surface0-30cm soil layer,0.6-0.7g kg-1in30-150cm soil depth and0.5g kg-1in150-200cm soil depth. Lucerne contributed286.0kg N ha-1for soil nitrogen pool of2m soil profile while milk vetch and bush clover consumed2204.8kg N ha-1and1209.6kg N ha-1from200cm soil profile nitrogen pool. Bare land lost880.8kg N ha-1from200cm soil profile.Soil C/N ratio was7.63at May2004before experiment. Milk vetch, bush clover and lucerne were significantly increased to9.34,8.94and8.45respectively at October2012while bare land was not change when compared with initial value. In the whole experimental period, grass legumes field and bare land soil C/N ratio was between7and10.Overall, lucerne has advantage at biomass production, water use efficiency, soil organic carbon sequestration and total nitrogen over milk vetch and bush clover. However, lucerne depleted soil water more and deeper than milk vetch and bush clover.
Keywords/Search Tags:Grass legumes, Lucerne, Milk vetch, Bush clover, Productivity, Soil water, Water use efficiency, Soil organic carbon, Soil total nitrogen, Soil organic carbon sequestration, Semi-arid region of the Loess Plateau
PDF Full Text Request
Related items