Penetration resistance and root growth of oats in tilled and untilled loess soil

Penetration resistance, bulk density, soil water content and root growth of oats were intensively studied in a tilled and an untilled grey brown podzolic loess soil. Bulk density and penetration resistance were higher in the top layer of the untilled soil compared with the tilled soil. In the latter, however, a traffic pan existed in the 25–30 cm soil layer which had higher bulk density and penetration resistance than any layer of the untilled soil. Above the traffic pan, rooting density (cm root length per cm³ of soil) was higher but below the pan it was lower than at the same depth in the untilled soil. Root growth was linearly related to penetration resistance. The limiting penetration resistance for root growth was 3.6 MPa in the tilled Ap-horizon but 4.6-5.1 MPa in the untilled Ap-horizon and in the subsoil of both tillage treatments. This difference in the soil strength-root growth relationship is explained by the build up of a continuous pore system in untilled soil, created by earthworms and the roots from preceding crops. These biopores, which occupy < 1% of the soil volume, can be utilized by roots of subsequent crops as passages of comparatively low soil strength. The channeling of bulk soil may counteract the possible root restricting effect of an increased soil strength which is frequently observed in the zero tillage system.     

Long-term tillage and rotation effects on soil microbial biomass,carbon and nitrogen

Summary Three mollisols, typical of the Palouse winter wheat region of eastern Washington and northern Idaho, were analyzed for microbial biomass, total C and total N after 10 years of combined tillage and rotation treatments. Treatments included till, no-till and three different cereal-legume rotations. All crop phases in each rotation were sampled in the same year. Microbial biomass was monitored from April to October, using a respiratory-response method. Microbial biomass, total C and total N were highest under no-till surface soils (0–5 cm), with minimal differences for tillage or depth below 5 cm. Microbial biomass differences among rotations were not large, owing to the relative homogeneity of the treatments. A rotation with two legume crops had the highest total C and N. Microbial biomass was significantly higher in no-till surface soils where the current crop had been preceded by a high-residue crop. The opposite was true for the tilled plots. There was little change in microbial biomass over the seasons until October, when fresh crop residues and rains had a strong stimulatory effect. The seasonal pattern of biomass in no-till surface soils reflected the dry summer/winter rainfall climate of the region. The results of this study show that numerous factors affect soil microbial biomass and that cropping history and seasonal changes must be taken into account when microbial biomass data are compared.Scientific paper no. 7634     

Retarded leaching of nitrate measured in monolith lysimeters in south-east Nigeria

At Onne in South-east Nigeria, drainage water was collected from four monolith lysimeters and analysed for nitrate. The lysimeters contained an acid sandy loam. At the start of the first rainy season two lysimeters received urea labelled with ¹⁵NO₃^– and two received no nitrogen fertilizer; all four were uncropped in the first year.
The peak concentrations of ¹⁵NO₃^– and of unlabelled (soil) NO₃^– were found after 2.5 pore volumes of water had passed through the lysimeters. Using the same soil in the laboratory after fine sieving, the peak concentration of tritiated water was found at 1 pore volume whereas nitrate leaching was retarded. The pattern of nitrate leaching was well described by miscible and immiscible models which included an adsorption coefficient for nitrate. Over the 2 years 81.4% of the ¹⁵N added at the start of the first rainy season was recovered in the drainage water.     

Role of soil and residue microorganisms in determining the extent of residue decomposition in soil

The effects of residue (wheat straw or sewage-sludge compost) incorporation in soil and the relative contribution of microorganisms in the residues, or in the soil to decomposition of the added residue, (CO₂ production) was evaluated in an incubation experiment. All residues and soils were adjusted to 33 kPa moisture tension and maintained at 25°C under a constant flow of CO₂-free air for 72 days. Residue decomposition was determined by monitoring CO₂ evolution from the treatments.

Mixing an aged sewage-sludge compost (10%, 224 Mg ha⁻¹) with soil stimulated decomposition of the compost 1.64-fold when compared with any of the localized placements, and indicated that the indigenous soil microorganisms were the major contributors to the transformations of this mature compost. Wheat straw was populated with organisms capable of decomposing readily-available substrates in the straw during the first stage of the decomposition, whereas it appeared that soil organisms contributed to an acceleration of straw decomposition during the final stages. After 65 days approx. 30% of the added wheat straw C had been evolved as CO₂. Soil basidiomycetes doubled the extent of decomposition when the indigenous decomposers in wheat were inactivated by γ-irradiation. Model equations are presented for residue decomposition relative to time.     

Exchange of greenhouse gases between soil and atmosphere: interactions of soil physical factors and biological processes

This review examines the interactions between soil physical factors and the biological processes responsible for the production and consumption in soils of greenhouse gases. The release of CO₂ by aerobic respiration is a non‐linear function of temperature over a wide range of soil water contents, but becomes a function of water content as a soil dries out. Some of the reported variation in the temperature response may be attributable simply to measurement procedures. Lowering the water table in organic soils by drainage increases the release of soil carbon as CO₂ in some but not all environments, and reduces the quantity of CH₄ emitted to the atmosphere. Ebullition and diffusion through the aerenchyma of rice and plants in natural wetlands both contribute substantially to the emission of CH₄; the proportion of the emissions taking place by each pathway varies seasonally. Aerated soils are a sink for atmospheric CH₄, through microbial oxidation. The main control on oxidation rate is gas diffusivity, and the temperature response is small. Nitrous oxide is the third greenhouse gas produced in soils, together with NO, a precursor of tropospheric ozone (a short‐lived greenhouse gas). Emission of N₂O increases markedly with increasing temperature, and this is attributed to increases in the anaerobic volume fraction, brought about by an increased respiratory sink for O₂. Increases in water‐filled pore space also result in increased anaerobic volume; again, the outcome is an exponential increase in N₂O emission. The review draws substantially on sources from beyond the normal range of soil science literature, and is intended to promote integration of ideas, not only between soil biology and soil physics, but also over a wider range of interacting disciplines.     

Fall Armyworm Damaged Maize Plant Identification using Digital Images

The objectives of precision agriculture are profit maximisation, agricultural input rationalisation and environmental damage reduction, by adjusting the agricultural practices to the site demands. The fall armyworm (Spodoptera frugiperda) is one of the most important maize pests in Brazil and the use of insecticide is the main control method. It is believed that site-specific control can be implemented by using a machine vision system. The objective of this work was to develop and evaluate an algorithm at simplified lighting conditions for identifying damaged maize plants by the fall armyworm using digital colour images. Images of damaged and non-damaged maize plants were taken in eight different stages and in three different light intensities. The proposed algorithm had two stages: the processing and the image analysis. During the first stage, the images were processed to create binary images where the leaves were segmented from the other pixels. At the second stage, the images were subdivided into blocks and classified as ‘damaged’ or ‘non-damaged’ depending on the number of objects found in each block. The algorithm correctly classified 94·72% of 720 images.     

Comparative effects of applying leguminous and non-leguminous green manures and inorganic N on biomass yield and nitrogen uptake in flooded rice (<Emphasis Type="Italic">Oryza sativa</Emphasis> L.)

The beneficial role of green manures in rice production is generally ascribed to their potential of supplying plant nutrients, particularly nitrogen (N). However, the mechanisms through which green manures enhance the crop productivity are poorly understood. Pot experiments were conducted using a ¹⁵N-tracer technique: (1) to compare the biomass production potential of sesbania (Sesbania aculeata Pers.) and maize (Zea mays L.) as green manuring crops for lowland rice and (2) to compare the effect of the two types of green manure and inorganic N on the dry matter accumulation and N uptake by two rice (Oryza sativa L.) cultivars, viz. IR-6 and Bas-370. Although maize produced three times higher shoot biomass compared with sesbania, the latter showed higher N concentration; and thus the total N yield was similar in the two types of plants. Applying the shoot material of the two plants to flooded rice significantly enhanced the dry matter yield and N uptake by the two rice cultivars, the positive effects generally being more pronounced with sesbania than with maize amendment. The difference in the growth-promoting potential of the two plant residues was related more to an increased uptake of the native soil N rather than to their direct role as a source of plant-available N. A positive added nitrogen interaction (ANI) was observed due to both plant residues, the effect was much more pronounced with the application of sesbania than with maize residues. In both rice cultivars, inorganic N also caused a substantial ANI, particularly at higher application rate. Losses from the applied N were 2–3 times lower from sesbania, compared with maize treatment. Green manuring with sesbania also caused much lower N losses than the inorganic N applied at equivalent or higher rates. The overall benefit of green manuring to rice plants was higher than inorganic N applied at comparable rates. The two rice cultivars differed in their response to green manuring, IR-6 generally being more responsive than Bas-370.     

孔隙结构图像分析中不同试验因素对分析结果的影响

研究了不同试验因素 (包括图像分辨率、土壤切片定向性、分析区域大小等 )对孔隙结构图像分析结果的影响以及试验误差 ,并简要介绍了用于分析土壤孔隙结构的土壤切片及数字图像的制备技术。结果表明 :不同试验因素对分析结果均会产生一定的影响 ,试验误差约在 1 0 %。这表明同一研究中应保持试验条件的相对一致以保证分析结果的可靠性和可比性     

十种土壤有效磷测定方法的比较

Ｏｌｓｅｎ[1 ] 、Ｂｒａｙ Ｋｕｒｔｚ1 [2 ] 、Ｍｅｈｌｉｃｈ3[3] 、Ｍｏｒｇａｎ[4] 、Ｖｅｒｍｏｎｔ1 [5] 和Ｖｅｒｍｏｎｔ2 [5] 等法是用于确定土壤有效磷含量的主要常规方法。根据土壤有效磷测定结果可为农户提供施肥建议以及预测施用磷肥或家畜粪肥后的经济效益等[6]     

Recovery of cover-crop-N in the soil-plant system in the Guinea savannah zone of Ghana

In order to understand the efficiency of residue-N use and to estimate the minimum input required to obtain a reasonable level of crop response, it is important to quantify the fate of the applied organic-N. The recovery of N from ¹⁵N-labelled Crotalaria juncea was followed in the soil and the succeeding maize crop. Apparent N recovery (ANR) by maize from unlabelled Crotalaria juncea, Crotalaria retusa, Calopogonium mucunoides, Mucuna pruriens and mineral fertilizer at three locations were also evaluated. The maize crop recovered 4.7% and 7.3% of the ¹⁵N-labelled C. juncea-N at 42 days after sowing (DAS) and at final harvest, respectively. The corresponding ¹⁵N recovery from the soil was 92.4% and 58.5%. The highest mean ANR of 57.4% was with mineral fertilizer, whereas the mean ANR of 14.3% from C. retusa was the lowest. A large pool substitution and added-N interaction effect was observed when comparing N recovery from the labelled and unlabelled C. juncea. The amount of residue-N accounted for by the isotope dilution method at 42 DAS was 97.1% and at final harvest 65.8%. The large residue-N recovery in the soil organic-N pool explains the residual effect usually observed with organic residue application.