短花针茅荒漠草原不同载畜率对土壤的影响
Effect of stocking rate on Stipa breviflora desert steppe soil
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摘要: 以内蒙古自治区乌兰察布短花针茅荒漠草原为研究对象, 通过9 a的定位试验, 研究放牧对土壤理化性状的影响, 旨在揭示不同载畜率条件下草原土壤退化的过程和机制, 以便采取合理的放牧管理措施, 遏制草原退化, 促进草地畜牧业可持续发展。试验在短花针茅荒漠草原设定4个载畜率水平, 重复3次, 以成年蒙古羯羊为供试绵羊, 从2004年开始小区放牧试验, 每年放牧期为6月初到11月底, 每天放牧时间为早6:00至晚18:00, 放牧试验2012年结束后, 通过对草原土壤理化性质的分析, 得出主要结果如下: 持续放牧9 a, 土壤表层含水量随着载畜率的增加显著降低(P<0.05), 载畜率对土壤机械组成、pH及速效磷和速效钾含量的影响未达显著水平(P>0.05); 0~10 cm土层土壤有机质含量在重度放牧处理下显著低于(P<0.05)其他处理; 土壤容重随着放牧时间的延长下降17.25%; 随着放牧强度的增加, 土壤砂粒含量呈增加趋势, 黏粒含量有所降低; 土壤速效磷、速效钾含量随载畜率升高而降低; 2012年重度放牧降低了土壤呼吸速率(P<0.05)。结合载畜率与年度互作分析, 经过9 a的持续放牧, 短花针茅荒漠草原放牧还没有从本质上引起草地土壤理化性状的严重退化, 但从土壤有机质含量来看, 土壤出现了一定程度的退化现象。Abstract: Grassland grazing ecosystem is one of the most efficient consumption systems of the terrestrial ecosystem. There are few repeated studies on long-term effects of stocking rate on stability of grazing ecosystems. With Inner Mongolia Wulanchabu Stipa Breviflora desert steppe as a case study, nine years stationary experiment was conducted to study the effect of grazing on soil physical and chemical properties. The study tested the processes and mechanisms of soil degradation at different stocking rates with the aim of beneficial adoption of reasonable grazing management measures and promoting sustainable development of grassland animal husbandry. A randomized complete block design was set up with four stocking rate treatments and three replicates. The stocking rate treatments included the control non-grazed enclosure (CK), light stocking rate (LG), moderate stocking rate (MG) and heavy stocking rate (HG). Adult Mongolia sheep were used in continuous grazing system from June to November of each year in 2004–2012. The stocking rates were 0 sheeps·hm2 (CK), 0.91 sheeps·hm2 (LG), 1.82 sheeps·hm2 (MG) and 2.71 sheeps·hm2 (HG). Soil physical and chemical properties were measured in 2004–2012. The results showed that soil water content in the topsoil decreased significantly with increasing stocking rate after 9 years of continuous grazing. Soil bulk density decreased by 17.25% with extended grazing time (P < 0.05), but not significantly changed with stocking rate. The stocking rate had no significant influence on soil mechanical composition, pH, and contents of available phosphorus and potassium. However, soil organic matter significantly decreased (P < 0.05) in the 010 cm soil depth under HG treatment compared with other treatments. With increasing stoking rate, the content of sand in the soil increased and that of clay decreased. Also HG treatment significantly decreased soil respiration rate in 2012. Based on statistical results of stocking rate, stocking year and their interactions, soil physical and chemical conditions of S. breviflora desert steppe did not significantly change over the nine years of grazing. However, organic matter apparently showed a certain degree of degradation. Because of resilience, hysteresis and complexity of natural soil systems, it was recommended that studies on the effects of stocking rates on soil bulk density should be done for longer time periods.