摘要:

Abstract.The laboratory, spatial and temporal components of variation associated with sampling soil for the measurement of pH, organic matter and extractable P, K, Mg, S, Cu, and Co were studied over two years using soil samples from 15 farms in S.E. Scotland. On each farm a selected field was divided into 4–8 sectors, and sampled three times each year, in June, August and October, by bulking 25 cores taken in a ‘W’ pattern. Analysis of variance showed that inter‐field variation was greater than that between sampling dates for most of the properties measured. Restricted Maximum Likelihood Estimation showed that for all elements except K and S the variation between fields was greater than that within a field. Temporal variation was usually smaller than spatial, but K and Co showed similarly small temporal and spatial variations. Variation associated with laboratory procedures was much less than either spatial or temporal variation except for S, most of the total observed variation of which resulted from laboratory error. It is suggested that the most cost effective field sampling technique is to split a field into sectors, sample each individually and analyse a bulked sample made up from the

ISSN:0266-0032    

DOI:10.1111/j.1475-2743.1994.tb00448.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Abstract.The variability of five soil series developed in sedimentary formations in southeastern Nigeria and mapped from aerial photographs was investigated in relation to texture, soil reaction, organic carbon, total nitrogen, exchangeable bases, exchangeable acidity, cation exchange capacity and available phosphorus. Air photo delineation of the five soil series was based on terrain physiography alone. Most of the soil series were very variable in available phosphorus, but the coefficients of variation for other soil properties were less than the 33%) threshold adopted for within‐series homogeneity critical for land use management. Soil series mapping at 1:50000 scale based on aerial photographs is therefore a cheap, rapid technique, which gives a satisfactory basis for land management to improve productivity and decrease soil degradation in Nigeri

ISSN:0266-0032    

DOI:10.1111/j.1475-2743.1994.tb00449.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Abstract.Analysis of agro‐climatic conditions forms the first stage of physical land evaluation. Monthly rainfall, potential evapotranspiration and air temperature data are analysed by the agro‐climatic module of the Jamaica Physical Land Evaluation System (JAMPLES). Dependable rainfall (R75), the minimum amount exceeded in a given time period in 75% of the years, ranges from 537 to 5332 mm/yr at the 141 recording stations under review, and mean potential evapotranspiration (PET) ranges from 1120 to 1580 mm/yr. Annual R75/PET ratios range from 0.3–5.0 island‐wide and regional differences permit delineation of four ‘moisture availability’ zones. These are subdivided with respect to the length of the ‘dependable’ growing periods (DGP) and dry periods. The DGP is less than 2 months in the southern coastal plains and 12 months long in the north‐eastern part of the island. Mean daily air temperature decreases from 26 to 13°C with elevation, permitting the delineation of five temperature classes. Suitable regions for growing particular crops can be determined with the Jamaica Geographical Information System (JAMGIS), which includes a digitized version of the 1:250000 map of agro‐climatic zones. More specific land suitability assessments, taking soil conditions and feasible land management practices into account, are prepared with the physical land evaluati

ISSN:0266-0032    

DOI:10.1111/j.1475-2743.1994.tb00450.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Abstract.The effects of deep tillage, straw mulching and farmyard manure on maize growth in loamy sand and sandy loam soils were studied in experiments lasting three years. Treatments included all combinations of conventional tillage (10 cm deep) and deep tillage (35–40 cm deep), two farmyard manure rates (0 and 15 t/ha) and two mulch rates (0 and 6 t/ha), replicated three times in a randomixed block design.Deep tillage decreased soil strength and caused deeper and denser rooting. Mulching decreased maximum soil temperature and kept the surface layers wetter resulting in better root growth. Farmyard manure also improved root growth, and the crop then extracted soil water more efficiently. All three treatments increased grain yield in the loamy sand, but in the sandy loam only tillage and farmyard manure increased yields significantly. Deep tillage and straw mulch effects varied with soil type and amount of rainfall in the growing season. In the loamy sand the mean responses to deep tillage and mulching were largest in a dry year. A tillage‐mulch interaction was significant in the loamy s

ISSN:0266-0032    

DOI:10.1111/j.1475-2743.1994.tb00451.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Abstract.The presence of spring barley plants increased the numbers of nematodes, particularly of plant‐feeders, compared with fallow plots in a Scottish organic farming system. The addition of farmyard manure (FYM) had no detectable effect on nematode populations but poultry manure (PM) caused a considerable increase. The application of PM also altered the types of nematode present and favoured bacterial‐feeders and rhabditids in particular. These changes suggest that PM causes shortterm (within a growing season) increases in microbiological activity and nutrient cycling, whereas FYM is more likely to bring about long‐term ch

ISSN:0266-0032    

DOI:10.1111/j.1475-2743.1994.tb00452.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Abstract.The long‐term effects of land clearing methods (manual, shear blade, tree‐pusher/root‐rake combination, traditional), tillage systems (disc ploughing, mechanized no‐tillage, traditional) and cropping systems (annual cropping, alley cropping, graxed pasture) on surface soil physical and chemical properties were evaluated on an Alfisol in south‐western Nigeria ten years after land clearing. Long‐term soil physical degradation was greatest after mechanized land clearing or tillage systems. The erosion resulting from soil compaction with mechanized land management systems resulted in exposure of subsoil. Cropping system had no significant effect on soil physical properties. Alley cropping decreased exchangeable calcium and pH, and increased total acidity mainly through the greater demand for calcium by the hedgerow species. Grazed pasture depleted exchangeable potassium because it was taken up by the grass and exported from the site by the cattle following consumption o

ISSN:0266-0032    

DOI:10.1111/j.1475-2743.1994.tb00453.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Abstract.Field studies at five locations on farmer's fields irrigated with residual sodium carbonate water (RSC) indicated that gypsum applications at the rate of 100% of the gypsum requirement of soil plus the quantity of gypsum required to neutralize RSC in excess of 4 mEq/1 decreased SAR values, and improved infiltration rate, crop emergence and wheat grain yields. The soil pH decreased by 0.3–0.4 units. Once soils have been ameliorated by this treatment, further small applications of gypsum are needed to decrease the RSC in irrigation water and avoid further soil deterioratio

ISSN:0266-0032    

DOI:10.1111/j.1475-2743.1994.tb00454.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Abstract.Topsoil (0–20 cm) and subsoil (60–100 cm) properties are compared at agricultural and nearby natural vegetation sites in São Paulo State. Differences are related to land use and climate, in order to estimate soil carbon storage under various ecosystems and also to study the effects of high‐input agriculture on the chemical composition of soils with low activity clays. Within each land use, organic carbon in the topsoil is most strongly related to clay + silt content. This relationship is stronger for cropped, short savannah (cerrado) and tall savannah (cerradão) sites than for semi‐deciduous and evergreen forest sites. Losses of topsoil carbon with cropping can be predicted if the initial carbon and the clay+silt contents are known. The greatest carbon losses after long term cultivation occurred in forest mineral topsoils, ranging from 6% for perudic clayey soils to 37% for ustic sandy soils. No significant difference in carbon content was found between the paired savannah‐cultivated sites. In most of the originally less fertile soils cation exchange capacity was greater in the cultivated topsoil (Ap) than in the topsoil under savannah or forest (A1), probably because of liming and phosphate fertilization. Most subsoils at agricultural sites show increases in exchangeable bases (mainly Ca) and base saturation, but no significant c

ISSN:0266-0032    

DOI:10.1111/j.1475-2743.1994.tb00455.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Abstract.Crop responses to applied potassium fertilizers are erratic in many arid and semi‐arid soils. The potassium supplying potential of river‐bed sediments and release of interlayer potassium from eleven alkaline soils were measured in two separate experiments. Sediments from the Chenab and Ravi Rivers in Pakistan were exhausted of potassium by successively growing wheat, maize, mungbean, and wheat in them for a total of 200 days, using Hoagland solution to supply optimum amounts of other nutrients. Cumulative plant dry matter yield was significantly greater on the Chenab sediments. The quantities of potassium supplied to plants from the sediments of the two rivers were also significantly different.Interlayer potassium was extracted for 1230 minutes from a Udic Haplustalf (Pindorian series) by twelve different solutions each with the same electrolyte content (100 cmol). The sodium adsorption ratios (SAR) of the solutions were adjusted to 5, 10, 25, and 50, each with Ca: Mg ratios of 25:75, 50: 50 or 75:25, using solutions of sodium, calcium and magnesium chloride. The potassium released from the soil was inversely related to solution SAR. Increasing proportions of magnesium relative to calcium in solution favoured the release of potassium, except in the SAR 50 solution. Significantly different quantities of potassium were extracted by various solutions. Maximum potassium (442 mg/kg) was extracted by SAR 5 solution with a Ca: Mg ratio of 25:75. Interlayer potassium subsequently removed by this solution from 11 alkaline soils ranged from 407 to 499 mg/kg. The potassium released from all but three of the soils was related to their clay content (r= 0.72;n= 8). The release of potassium from the soils followed the Elovich function. The intercept (X1) and slope (X2) estimated for the function was related to potassium released (y) by the equation:y=−1.13 + 2.74X1−0.014X2(r= 0.998;n= 8)The results imply that river sediments treated with irrigation water containing magnesium and sodium ions can contribute substantial amounts of available potassium for plant

ISSN:0266-0032    

DOI:10.1111/j.1475-2743.1994.tb00456.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Abstract.At Woburn Experimental Farm (SE central England) sulphur (S) deficiency symptoms occurred in a winter oilseed rape crop grown in Lansome field on soil of the Cottenham series, but not on the Blithe series soil in the adjacent Mill Dam Close field. At maturity, the two crops produced a similar amount of dry matter but seed yield and harvest index were significantly less in Lansome. Total S uptake of the crop in Lansome was less than half of that in Mill Dam Close, which was similar to the amount normally found in a S sufficient crop. Both soils are of light texture (loamy sand and sandy clay loam for the Cottenham and Blithe series, respectively), and there was little difference in the extractable S concentration in the topsoils between the two fields. However, more extractable S was found in the subsoil of Blithe series, because it contains more free Fe and Al oxides and has a lower pH. These results show that any evaluation of the soil S supply needs to take into account the pool of available S in the subsoil.

ISSN:0266-0032    

DOI:10.1111/j.1475-2743.1994.tb00457.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY