Microbial populations,enzyme activities and nitrogen-phosphorus-potassium enrichment in earthworm casts and in the surrounding soil of a pineapple plantation

Summary Total populations of bacteria and fungi, dehydrogenase activity (as a measure of total potential microbial activity), and urease and phosphatase activities were determined in earthworm casts and surrounding laterite soils planted to pineapple. The casts contained higher microbial populations and enzyme activities than the soil. Except for fungal populations, statistically significant (P = 0.05) increases were found in all other parameters. Microbial populations and enzyme activities showed similar temporal trends with higher values in spring and summer and lower values in winter. The earthworm casts contained higher amounts of N, P, K and organic C than the soil (P = 0.05). Selective feeding by earthworms on organically rich substrates, which break down during passage through the gut, is likely to be responsible for the higher microbial populations and greater enzyme activity in the casts.     

The effect of disturbance by Phellinus weirii on decomposition and nutrient mineralization in a Tsuga mertensiana forest

Summary Microbial biomass in the upper 7 cm of soil and needle decomposition on the forest floor were measured seasonally for 10 months in a mountain hemlock (Tsuga mertensiana) old-growth forest and in a regrowth forest after Phellinus weirii, a root-rot pathogen infection, had caused disturbance. The microbial biomass was higher in the old-growth forest soil than in the regrowth forest soil. However, T. mertensiana needle decomposition rates were higher in the regrowth than in the old-growth forest. Total N, Ca, Fe, Cu, and Zn concentrations in needles increased during the 1st year of decomposition in both the old and the regrowth forests, but P, K, Mg, Mn, and B concentrations decreased. N, P, K, Mg, Cu, and Zn concentrations were lower in regrowth than in old-growth decomposing needles. During mineralization, needles in the regrowth forests released more N, P, and K as a result of higher needle decomposition rates. Our results suggest that higher needle decomposition rates increased the mineralization of N, P, and K, which may lead to increased soil fertility and faster tree growth rates in the regrowth forest.     

低丘红壤有机碳库的密度及变异

在中国科学院红壤生态实验站,采样分析了不同利用方式下土壤有机C 库的密度及其变异。结果表明,低丘红壤有机C 的密度0 ~ 20cm为(2.09 0.69) kg/m2,0 ~ 100 cm为(5.01 1.46) kg/m2; 全N密度0 ~ 20 cm为(0.20 0.07) kg/m2, 0 ~ 100 cm为(0.59 0.14) kg/m2。从裸地到稀疏荒草地,0 ~ 20 cm和0 ~ 100 cm土壤有机C 密度可以提高1.0 kg/m2和1.7 kg/m2;而从稀疏荒草地到人工林地或园地,0 ~ 20 cm和0 ~ 100 cm土壤有机C 密度可以提高0.7 kg/m2和0.9 kg/m2;稀疏荒草地如果开垦利用为水田,经长期培肥达到高度熟化,则0 ~ 20 cm和0 ~ 100 cm土壤有机C 密度可以提高2.3 kg/m2和4.4 kg/m2。即使不同类型的人工林地和园地之间,0 ~ 20 cm和0 ~ 100 cm土壤有机C 的密度差异也可达到1.0 kg/m2和3.5 kg/m2。不同地形部位之间0 ~ 20 cm和0 ~ 100 cm土壤有机C 密度差异达到1.3 kg/m2和2.9 kg/m2,全N密度差异达0.1 kg/m2和0.3 kg/m2;不同肥力水平之间0 ~ 20 cm和0 ~ 100 cm土壤有机C 密度差异达到1.5 ~ 2.2 kg/m2和2.8 ~ 4.1 kg/m2,全N密度差异达0.07 ~ 0.11 kg/m2和0.20 ~ 0.23 kg/m2; 强烈侵蚀可以降低0 ~ 20 cm和0 ~ 100 cm土壤有机C 密度1.4 kg/m2和2.2 kg/m2。因此,通过调整土地利用方式,可以提高土壤有机C 库密度,增     

几种有机物对紫色土镉的溶出效应与吸附-解吸行为影响的研究

研究了天然有机物胡敏酸和富里酸 ,螯合剂EDTA和DTPA和四种简单有机酸对紫色土镉的溶出效应和吸附解吸行为的影响。结果表明 ,供试八种有机物均能显著促进镉从紫色土中的溶出。作用大小顺序为 :EDTA≥DTPA >柠檬酸 >胡敏酸 >草酸 >富里酸 >酒石酸≥水杨酸。有机物对土壤镉溶出和迁移的影响是其对土壤镉吸附和解吸综合作用的结果。有机物显著降低了紫色土对镉的吸附 ,其作用大小顺序与其对镉的溶出能力的相对大小顺序一致 ,同时也改变了吸附镉的解吸特性。有机物影响下 ,紫色土镉的吸附动力学模型以双常数方程拟合最佳。而吸附等温曲线以Freundlich方程拟合最好 ,吸附常数n与有机物对土壤镉的溶出率之间存在良好的相关性。     

有机酸对土壤中镉的解吸及影响因素

研究了酒石酸和柠檬酸对两种不同处理土壤 (镉质土和污染土 )中Cd的解吸行为 ,探讨了介质pH值、支持电解质等对其解吸镉质土和污染土中Cd的影响。结果表明 ,随有机酸浓度升高 ,柠檬酸和酒石酸对镉质土和污染土中Cd的解吸率呈先降低后升高变化 ,出现一波谷 ,波谷位置与有机酸和土壤类型有关。当解吸液起始pH值由 2升至 8时 ,柠檬酸对镉质土和污染土中Cd的解吸率呈降低—升高—降低的变化 ,先后出现一波谷和一波峰 ,且柠檬酸浓度高时变化趋势尤为明显 ;而酒石酸对镉质土和污染土中Cd的解吸率则一直降低。解吸液中支持电解质浓度提高 ,酒石酸对镉质土和污染土中Cd的解吸率增大 ,且以KCl为支持电解质时的解吸率要高于KNO3。     

火烧对土壤性质的影响

火烧以后 ,土壤的各种性质会发生较大变化 ,原因是火向土壤中施加了热量、灰烬 ,并且改变了土壤环境和微气候 ,土壤性质也可因植被和生物活性的改变而发生相应的变化。本文对火烧后土壤生态系统中养分的浓度、有效性、迁移性 ,土壤中的生物和酶活性 ,土壤有机碳库等的变化进行了综合评述 ,以期为森林火灾、草地烧荒后的土壤管理等提供理论参考。     

植物篱枝叶有机碳分解研究

研究植物篱枝叶的分解和养分矿化过程对该模式下养分的有效利用具有重要意义。在金沙江干热河谷坡耕地上利用分解袋法对新银合欢、山蚂蝗等 6个植物篱树种枝叶的分解进行了研究 ,结果显示山蚂蝗和新银合欢分解最快 ,前 2个星期有机碳分解了48 6 %和 5 0 0 % ;山毛豆和云南合欢次之 ,前 4星期有机碳累积分解量为 5 1 5 %和 45 6 % ;圣诞树和黑荆树分解最慢 ;将枝叶埋入土壤中比覆盖地表分解快。有机碳的分解规律可以用单指数模型Ct=C0 (1 e kt)和双指数模型Ct=C0 1 (1 e k1t) C0 2 (1 e k2 t)拟合 (式中 ,Ct 为有机碳累积分解量占全碳百分数 ,C0 、C0 1 和C0 2 分别为易分解有机碳和难分解有机碳百分数 ,k和k1分别为易分解有机碳分解常数 ,k2 为难分解有机碳分解常数 ) ,双指数模型更具合理性。研究表明有机碳的累积分解量与枝叶初始C/N比呈负相关 ,枝叶分解速度可用有机碳 (或易分解有机碳 )半减期来衡量。     

土壤有机硫矿化动力学特征及影响因素

利用开放培养系统，分别在20℃和30℃，好气和淹水条件下研究了四种土壤（黑土、褐土、黄棕壤和红壤）有机硫矿化特征。结果表明，30℃条件下土壤有机硫累积矿化量显著高于20℃下的矿化量（P＜0．01）。20℃和30℃好气条件下累积矿化量分别为17．53－24．35mg kg^-1和34．20－54．33mg kg^-1，分别占有机硫总量的2．5％－6．5％和5．－14．5％，20℃和30℃淹水条件下累积矿化量分别为18．14－21．15mg kg^-1和26．86－30．63mg kg^-1，分别占有机硫总量的2．6％－5．6％和4．0％－7．7％。好气和淹水下30℃与20℃的有机硫累积矿化量之比分别为1．85－2．23和1．28－1．71。用一级动力学方程和双倒数方程计算土壤有机硫矿化势（S0）表明，20℃好气培养时S0分别为17．82－24．88mg kg^-1和17．83－27．7mg kg^-1，S0分别为17．50－21．49mg kg^-1和19．19－22．50mg kg^-1,30℃淹水条件下S0分别为28．26－35．87mg kg^-1和26．59－34．25mg kg^-1。土壤有机硫矿化速率常数（K）和矿化量达50％矿化势（S0）所需的时间（K1）受不同土壤和培养温度的影响，都可用一级动力学方程和双倒数方程来评价。碳键硫对有机硫矿化的贡献较大，尤其在淹水条件下更明显。     

Tillage and crop sequence effects on organic carbon and total nitrogen content in an irrigated Alberta soil

A better understanding of tillage effects on soil organic matter is vital for development of effective soil conservation practices. The objective of this research is to determine the effect of tillage and crop sequence on soil organic carbon (OC) and total nitrogen (TN) content in an irrigated southern Alberta soil. A field experiment was conducted using a split–split plot design from 1994 to 1998 in Alberta, Canada. There were two crop sequences (Sequence 1: spring wheat (Triticum aestivum L.)–sugar beet (Beta vulgaris L.)–spring wheat–annual legume; and Sequence 2: spring wheat–spring wheat–annual legume–sugar beet) and two tillage practices (CT: conventional tillage and MT: minimum tillage). Surface soil under MT had significantly higher OC (30.1 Mg ha⁻¹) content than under CT (28.3 Mg ha⁻¹) after 4 years of treatment. The MT treatment retains crop residue at the soil surface, reduces soil erosion and slows organic matter decomposition, which are key factors in enhancing the soil fertility status of southern Alberta irrigated soils.     

Influence of management practices on soil organic matter changes in the Northern China plain and Northeastern China

Soil organic matter (SOM) is strongly related to soil type and management practices. Changes in government policy have brought drastic changes in farm management practices in the last two decades in rural China. This study investigates changes in SOM in two different soils: Ustepts and Udolls. Ustepts, in the North China Plain where the climate is warm and sub-humid, developed from an alluvial flood plain with organic matter <10 g kg⁻¹. Udolls, in Northeastern China where the climate is cool and sub-humid, developed from loess-like materials with organic matter >20 g kg⁻¹. Two locations for Ustepts and three locations for Udolls were used to collect 567 soil samples in 1980–1982 and again in 2000 for SOM analysis. Soil organic matter increased for Ustepts and decreased for Udolls soils over the sampling period, resulting from differences in fertilizer rates and crop residue input to soil. Higher fertilizer input and crop intensity and initially very low SOM content in Ustepts all contributed to greater OM input than oxidation release. In contrast, lower fertilizer input and crop intensity, and initially high SOM content in the Udolls, led to lower OM input than oxidation release. Increasing SOM content through higher mineral fertilizer input is a valuable option for sustainable agriculture production in areas where SOM is low and there is a shortage or potential shortage of food supply.