红壤旱地毛叶苕子不同翻压量下腐解及养分释放特征

为了探讨不同翻压量的毛叶苕子在红壤旱地的腐解及养分释放特征,采用尼龙网袋埋田法在江西东乡红壤甘薯地进行了180d的田间腐解试验,研究了低(15000kg/hm~2)、中(22500kg/hm~2)、高(30000kg/hm~2)3个翻压量下毛叶苕子的干物质腐解规律和养分释放率。结果表明,总体上毛叶苕子腐解存在前期迅速、后期缓慢的现象,翻压180d后毛叶苕子干物质的最终腐解率达到70.19%~84.18%。碳、氮、磷、钾、镁、硫、铜、锌均在翻压后的前20d大量释放,钙、锰的释放较慢,铁在翻压前期出现"富集"现象。增加翻压量不会改变毛叶苕子整体的腐解及养分释放规律,但会对养分的释放率和释放速率产生影响。不同翻压量下毛叶苕子碳、氮、磷、钾的释放率和释放速率分别可用幂函数y=ax~b和指数衰减模型v=v_0e~(-kx)进行拟合,回归分析表明增加翻压量对毛叶苕子碳、氮完全释放的延缓效应最大(延缓354~406d和791~1358d)、磷次之(延缓87~122d)、钾最小(延缓16~27d)。增加翻压量可以显著提高毛叶苕子碳、氮、磷、钾的释放速率,但仅局限于翻压后的前10或20d。增加翻压量后毛叶苕子大部分的养分仍在翻压后的前20d释放,后期的释放量并未得到大幅提高,为后茬作物"持续"供应养分的能力有限。因此,实际生产中应充分结合后茬作物的需肥特性,制定毛叶苕子合理的翻压量。本研究可为中国南方红壤旱地绿肥作物的科学利用提供理论依据。

Decomposition and nutrient release characteristics of different Vicia villosa green manure applications in red soil uplands of South China

Vicia villosa is commonly used as a green manure or pasture in north China.In order to provide a scientific basis for its use as green manure in south China,a study has been undertaken in winter-fallowed red soil uplands used for sweet potato crops in Dongxiang County,Jiangxi Province.The decomposition and nutri-ent release characteristics of Turkmen V .villosa were tested with different application amounts.Nylon net bags (30 cm×20 cm)were used to assess three application treatments:low (90 g fresh grass per bag,equiva-lent to 15000 kg/ha),medium (135 g fresh grass per bag,equivalent to 22500 kg/ha)and high (180 g fresh grass per bag,equivalent to 30000 kg/ha).The rates of dry matter decomposition and nutrient release were monitored at 10,20,30,60,90,120,150 and 180 days after application.The results showed that all three treatments decomposed rapidly over the first 20 days and then the release speeds slowed.The dry matter decomposition rate reached 60.59%-66.72% after 20 days and 70.19%-84.18% by the end of the experi-ment.Carbon (C),nitrogen (N),phosphorus (P),potassium (K),magnesium (Mg),sulphur (S),copper (Cu)and zinc (Zn)released rapidly in the first 20 days,reaching 62.1%-68.1%,71.5%-76.0%,70.4%-81.8%,97.3%-97.7%,75.6%-82.1%,73.4%-79.0%,78.6%-81.6% and 84.1%-88.4% respec-tively.Calcium (Ca)and manganese (Mn)released relatively slowly at first (43.5%-63.8% and 20.6%-35.9% after 20 days),but their release rates reached 86.0%-92.6% and 54.2%-76.7% respectively by the end of the experiment.Iron (Fe)was a significant “enrichment”phenomenon in the early stages but its release rate was ultimately very low.The general rules of decomposition and nutrient release did not change signifi-cantly with increasing application amounts.The release rates and speeds of C,N,P and K in the different ap-plications fitted well with both the power function formula y =ax b (all P <0.001 )and the exponential decay model v=v 0 e-kx (all P <0.01).Regression analysis showed that the delay effects of nutrient release caused by increasing application amounts were C and N>P>K,with the full release of these nutrients needing 354-406 d,791-1358 d,87-122 d and 16-27 d respectively.The release speeds of C,N,P and K improved signifi-cantly over the first 10 and 20 d after application,following which the values remained at extremely low levels. This pattern did not change significantly with higher applications.Therefore,the ability to continuously supply nutrients for following crops by increasing the application amounts of V .villosa is very limited.Optimum application amounts need to be determined by fully considering the fertilizer requirements of the following crops.