Soil organic matter, microbial biomass and enzyme activities in a tropical agroforestry system

 The effects of growing trees in combination with field crops on soil organic matter, microbial biomass C, basal respiration and dehydrogenase and alkaline phosphatase activities were studied in soils under a 12-year-old Dalbergia sissoo (a N₂-fixing tree) plantation intercropped with a wheat (Triticum aestivum) – cowpea (Vigna sinensis) cropping sequence. The inputs of organic matter through D. sissoo leaf litter increased and crop roots decreased with the increase in tree density. Higher organic C and total N, microbial biomass C, basal soil respiration and activities of dehydrogenase and alkaline phosphatase were observed in treatments with tree-crop combination than in the treatment without trees. Soil organic matter, microbial biomass C and soil enzyme activities increased with the decrease in the spacing of the D. sissoo plantation. The results indicate that adoption of the agroforestry practices led to an improved organic matter status of the soil, which is also reflected in the increased nutrient pool and microbial activities necessary for long-term productivity of the soil. However, tree spacing should be properly maintained to minimize the effects of shading on the intercrops. Received: 21 February 1997     

不同培肥途径对黑土有机质持续效应的研究

以农家肥、化肥、秸秆、绿肥等培肥物质为试验因素,研究长期定位试验耗竭阶段土壤有机质的持续效应。4年耗竭试验结果表明,各处理土壤有机质含量皆呈现明显下降趋势。其中,农家肥、秸秆、化肥三种肥料的持续效应的大小顺序依次是:农家肥>秸秆>化肥。玉米连作不施肥区下降幅度不明显。绿肥—玉米轮作区变化有起伏;休闲区缓慢下降。从每两个培肥物质的交互作用对土壤有机质的影响来看,农家肥和秸秆、化肥和秸秆之间有明显的正交互作用,而农家肥和化肥之间交互作用不明显。     

江西红壤性水稻土肥力特性及其管理

江西红壤性水稻土为２０２．８８２７万ｈｍ２。其肥力特征：１．土壤三要素营养不平衡,中低产田占７０．００％;２．缺硼钼少硅硫锌,影响土壤养分平衡;３．灌溉水能提供稍多Ｃａ、Ｍｇ,少量Ｓ、Ｓｉ、Ｋ、Ｎ,以补充土壤养分不足;４．耕层浅薄,障碍因素较多。管理：１．深耕培肥,增加土壤有机质;２．坚持有机无机肥配合,提高稻田肥力;３．合理施肥,协调养分平衡;４．开沟排水、搞好稻田沟系建设;５．水旱轮作、改革耕作制度。     

含氯离子土壤有机质分析方法的初步研究

本文探讨了用提前加Ｈ２ＳＯ４的方法来消除氯离子对测定土壤有机质的干扰。     

Ecosystem fertility and fallow function in the humid and subhumid tropics

The regeneration of natural vegetation (fallowing) is a traditional practice for restoring fertility of agricultural land in many parts in the tropics. As a result of increasing human population and insufficient fertilizer inputs, the ecosystem fertility functions of traditional fallows must now be improved upon via the use of managed fallows. Interactions between vegetation and soil determine nutrient losses and gains in crop—fallow systems and are influenced by fallow species, patterns and rates of biomass allocation, and crop and fallow management. Nutrient losses occur through offtake in crop harvests during the cropping phase and through leaching, runoff, and erosion in the cropping phase and the initial stage of fallows $#x2014; when nutrient availability exceeds nutrient demand by vegetation. Gains in nutrient stocks in later stages of fallow are generally more rapid on soils with high than low base status due to greater quantities of weatherable minerals and lack of constraints to N₂ fixation, deep rooting, and retrieval of subsoil nutrients by fallow vegetation. On low base status soils (exchangeable Ca < 1 cmol_c kg^–1), N₂ fixation and atmospheric inputs are likely to be the main sources of nutrient additions. On high base status soils limited by N, gains in N stocks by inputs from N₂ fixation and retrieval of subsoil nitrate can occur relatively rapidly; hence short-term fallows can often improve crop performance. Large losses of Ca associated with soil organic matter (SOM) mineralization and soil acidification during cropping and fallow establishment, combined with chemical barriers to root penetration, suggest that long-duration fallows (> 5 yr) are needed for recovery of cation stocks and crop performance on low base status soils. On both soils, however, residual benefits of fallows on crop yields usually last less than three crops.This revised version was published online in November 2005 with corrections to the Cover Date.     

Soil organic matter dynamics after the conversion of arable land to pasture

 Conversion of arable land (maize) to pasture will affect the soil organic matter (SOM) content. Changes in the SOM content were studied using a size- and density-fractionation method and ¹³C analysis. Twenty-six years of maize cropping had resulted in a depletion of carbon stored in the macro-organic fractions (>150 μm) and an increase in the <20 μm fraction. Maize-derived carbon in the upper 20 cm increased from 10% in the finest fraction (<20 μm) to 91% in the coarse (>250 μm), light (b.d. <1.13 g cm^–3) fractions. Pasture installation resulted in a rapid recovery of the total SOM content. Up to 90% of the pasture-derived carbon that was mineralized during maize cropping was replaced within 9 years. Especially the medium and coarse size (>150 μm) and light (b.d. <1.13 g cm^–3) fractions were almost completely regenerated by input of root-derived SOM. The amount of medium-weight and heavy macro-organic fractions (>150 μm; b.d. >1.13 g cm^–3) in the 0- to 20-cm layer was still 40–50% lower than in the continuous pasture plots. Average half-life times calculated from ¹³C analyses ranged from 7 years in the light fractions to 56 years in heavy fractions. Fractionation results and ¹³C data indicated that mechanical disturbance (plowing) during maize cropping had resulted in vertical displacement of dispersed soil carbon from the 0- to 20-cm layer down to 60–80 cm. Conversion of arable land to pasture, therefore, not only causes a regeneration of the soil carbon content, it also reduces the risk of contaminant transport by dispersed soil carbon. Received: 10 March 1998     

Carbon and nitrogen dynamics in ageing earthworm casts in grasslands of the eastern plains of Colombia

 The effects of a large species of anecic earthworm, Martiodrilus carimaguensis Jiménez and Moreno, on soil C and N dynamics were investigated in a native savanna and a man-made pasture of the eastern plains of Colombia. We compared, across time (11 months), the total C, total N, NH⁺ ₄ and NO^– ₃ contents in the earthworm casts, the underlying soil and the adjacent soil. Additional sampling of root biomass and macrofauna was performed. In the two management systems, the total C and N contents were higher in casts (4.33–7.50%) than in the bulk soil (2.81–4.08%), showing that the earthworms selected food substrates with high organic contents. In general, C contents significantly increased during cast ageing (+100%), possibly because of CO₂ fixation processes, dead root accumulation and/or macrofaunal activities in casts. In fresh casts, NH⁺ ₄ levels were very high (294.20–233.98 μg g^–1 dry cast) when compared to the soil (26.96–73.95 μg g^–1 dry soil), due to the intense mineralisation processes that occurred during the transit of soil and organic matter through the earthworm gut. During the first week of cast ageing, NH⁺ ₄ levels sharply decreased, while NH^– ₃ levels showed successive peaks in the casts, the underlying soil and the adjacent soil. These results suggested the rapid production of NO^– ₃ by nitrification processes in the fresh casts, followed by diffusion to the nearby soil, first vertically, then horizontally. After 2 weeks of cast ageing, NH⁺ ₄ and NO^– ₃ levels only showed slight variations, likely because of organic matter protection in stable dry casts. The root biomass was higher (1.6–4.7 times) below the old earthworm casts. The ecological significance of these results is discussed. Received: 22 October 1998     

亚种间杂交稻干物质生产积累及转换与籽粒充实度的研究

对亚种间、品种间杂交稻和常规稻的干物质生产积累、运转和籽粒充实度进行了比较研究。结果表明,亚种间杂交稻穗大粒多,增产潜力大。在整个生育过程中,一直具有较强的干物质生产优势;在抽穗至成熟期,干物质运转率高,其干重颖花比值小;籽粒充实度差的主要原因是“库大源不足”。     

抑制素主动免疫对母牛卵泡发育的影响

本试验以猪精液抑制素粗提物主动免疫母牛,研究了对母牛卵泡发育和内分泌的影响。免疫,母牛的卵泡发育率为１４５．５％,排卵率为１１８．２％,分别比对照组提高４５．５％和１８．２％。通过放射免疫法对免疫牛血液中ＦＳＨ,ＬＨ,Ｅ２水平测定发现,发情时免疫组母牛ＦＳＨ水平高于对照组,免疫组中多卵发育牛ＦＳＨ水平高于单卵牛,免疫组与对照组中ＬＨ水平相差不大,多卵牛发情时Ｅ２水平较高。     

不同生态型玉米生长特点的研究

在海拔600m处夏播玉米,对平丘紧凑型(A)、平丘平展型(B)、低山中熟型(C)、中山晚熟型(D)和高山早熟型(E)5个生态型玉米品种生长特点的研究表明：(1)D生态型的植株和穗位最高、穗高系数最大、叶数最多、单叶和单株面积最大、生育期最长、单株干物重最大,E生态型的这些值最小,其他生态型介于它们之间;(2)后期时间系数、后期干物质积累系数和后期净同化率的变化规律是E型＞A型＞B型＞C型＞D型;(3)收获指数A型＞B型、E型＞C型＞D型,分配指数B型＞C型＞A型＞Ｅ型＞D型。不同生态型玉米品种具有不同的植株生长、干物质积累和分配特点,这与各品种的地域来源、所适应的生态环境以及所处的育种阶段有关。