摘要:

Abstract.The effect ofMedicago arboreaon erosion on a burnt area was studied in experimental plots near Valencia, Spain, between 1989 and 1992. Its growth and development was studied, and its effect was compared with the natural vegetation (matorral) and bare soil.Medicagodecreased soil loss by 41.7% and runoff by 25.7% compared with bare soil. However, under natural vegetation soil loss was 27.5% less than underMedicago.

ISSN:0266-0032    

DOI:10.1111/j.1475-2743.1994.tb00466.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Abstract.Regression equations successfully allowed the calculation of water retained at—0.3 × 105Pa and–15 × 105Pa matric potentials from single soil characteristics, such as bulk volume or clay content, in clayey horizons derived in similar ways from a single parent material. It is possible to use these regression equations on other soils with similar clay fabrics. The fabric is expressed numerically using the pore volume associated with clay part

ISSN:0266-0032    

DOI:10.1111/j.1475-2743.1994.tb00467.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Abstract.Sisal production in Tanzania has declined sharply in the past two decades because of a decrease in the area grown and a decrease in yields. As sisal is cultivated without manuring, depletion of soil fertility is considered one of the main causes of the declining yields. This paper presents a balance of the macronutrients N, P, K, Ca and Mg for sisal grown in a plantation in NE Tanzania on deep, red clay soils (Ferralsols). Annual fibre yields declined from 2.5 t/ha in the 1960s to about 1 t/ha in the 1980s. Hybrid sisal is a demanding crop and in ten years, with a total fibre yield of 11 t/ha, about 260 kg of N, 40 kg of P, 385 kg of K, 890 kg of Ca and 330 kg of Mg are removed in the harvested leaves. A comparison of soils after two and three 10‐yr cycles of sisal production showed that in the third cycle the pH decreased by 0.5 units and that exchangeable bases were decreased by fifty per cent or more. The amounts of K, Ca and Mg removed from the soil were similar to those in leaves. However, soil analyses could not detect changes in total N and available P, possibly because of the large amount of total N in the soil and the lack of precision in the N and P analyses. In the Ferralsols, potassium is likely to become deficient first, followed by magnesium and calcium. The soil has little available P, and an increase in soil acidity may decrease it further and also create aluminium and manganese toxicities. In order to maintain sisal production, fertilization with P, K, Ca and Mg is necessary, and to improve yields N must also be applie

ISSN:0266-0032    

DOI:10.1111/j.1475-2743.1994.tb00468.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Abstract.Microbial transformations and chemical distribution of N were compared in two upland stagnohumic gley soils at the same site. In 1981 one soil was improved for more intensive agriculture by lime and fertilizer applications and reseeding with a grass/clover mixture. The other soil (referred to here as unimproved) was also reseeded in 1981, but no lime was added and the sward has subsequently reverted to rough grazing land. Improvement resulted in greater soil microbial activity. The improved soil showed greater rates of denitrification, net N immobilization and N fixation (acetylene reduction) and contained more microbial biomass N than the unimproved soil. However, no major differences in the distribution of organic N fractions were detected. This indicates that a large amount of the soil N present before improvement did not undergo mineralization and remained unavailable to plants.

ISSN:0266-0032    

DOI:10.1111/j.1475-2743.1994.tb00469.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Abstract.Each year since 1986 information has been collected about the farming systems at intersections of a nationwide 7 km square grid in Denmark. These management data and corresponding soil analyses were used in the model DAISY to simulate water and nitrogen dynamics. The model was validated with respect to harvested dry matter yield and nitrogen content in the soil. Simulated nitrate leaching from farmland areas from 1 April 1989 to 31 March 1993 was related to precipitation zones, soil type, fertilizer strategies and cropping systems. The mean simulated nitrate leaching for the whole of Denmark was 74 kg N/ha/yr, with a large yearly variation in the period considered. The simulated nitrate leached from soils with a sandy subsoil corresponded to 51% of the applied fertilizer, twice that leached from soils with a loamy subsoil. The application of pig manure resulted in average leaching losses of 105 kg N/ha/yr. The simulated nitrate leaching losses at sites where only artificial fertilizer was applied were in the following order: cereal with undersown grass

ISSN:0266-0032    

DOI:10.1111/j.1475-2743.1994.tb00470.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Abstract.Nitrate leaching in lysimeters containing a tropical sandy agricultural soil was studied over two summers with maize (Zea maysL.) and one winter season with wheat (Triticum aestivumL.). The treatments included two moisture regimes and two nitrogen sources, cattle manure and inorganic fertilizer‐N (either ammonium nitrate or ammonium sulphate) applied at 100 kg N/ha in the summers. Neither manure nor fertilizer‐N was applied in the intervening winter. Leachate volume from the manured lysimeters was mostly larger than from fertilized ones because of poor growth and less evapotranspiration. The largest seasonal nitrate loads (17–39 kg N/ha) were obtained in the wet summer immediately after installation of the lysimeters. Nitrate loads in winter (3.7–18.6 kg N/ha) were larger than those obtained in fertilized (0.6 and 9.3 kg N/ha) and manured (0.3 and 3.0 kg N/ha) lysimeters for the two moisture regimes in the second summer. The drier conditions in the second summer decreased N‐mineralization and leaching

ISSN:0266-0032    

DOI:10.1111/j.1475-2743.1994.tb00471.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Abstract.The impact of lead shot on soils and crops was examined at a clay pigeon shooting site in northern England. Topsoil cores were collected along a 300 m transect from the shooting range, and the numbers of lead shot pellets per soil core, total and ‘plant‐available’(0.5macetic acid extractable) lead concentrations, organic matter content, pH and cation exchange capacity were determined. The number of oilseed rape plants and their stem diameters were recorded in 1 m2quadrats placed at the soil sampling locations. Total and ‘plant‐available’ lead concentrations in the soil were most but plant numbers per m2and mean stem diameters were least in the area of greatest lead shot deposition. Total lead concentrations in the soil commonly exceeded 5000 mg/kg; these are considerably greater than threshold ‘trigger’ concentrations proposed by the Department of the Environment, above which soils are considered to be contaminated and warrant further investigation. Concentrations of lead in the oilseed rape plants themselves were also largest in the area of most intense lead shot deposition; in root samples the lead concentration exceeded 400 mg/kg. The management and remediation of contaminated soils at the clay pigeon shooting sit

ISSN:0266-0032    

DOI:10.1111/j.1475-2743.1994.tb00472.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Abstract.Rooting depth, watertable depth and oxygen regime were measured in plots of Sitka spruce, lodgepole pine and a 50% mixture of each species planted on a deep unflushed blanket peat. The water‐table was about 10 cm deeper and roots occurred about 2 cm deeper under the pine than under the spruce or the mixture. In addition the mean concentration of oxygen at 50 cm depth was significantly larger under the pine and the mixture than under the spruce, showing that the rapid early growth of the pine had started to dry the peat. There was no evidence of any improvement in the growth of the spruce in the mixture compared to the pure Sitka spruce, suggesting that the expected nursing benefit had not occurre

ISSN:0266-0032    

DOI:10.1111/j.1475-2743.1994.tb00473.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Abstract.Nepal is facing a serious problem of being unable to maintain soil fertility in agriculture and forestry. Land use practices initiated over the past 10–15 years have resulted in insufficient nutrient inputs, while biomass use and production have increased. Changes in forest soil fertility have resulted from intensive use of forest biomass for animal feed and collection of forest litter for use in agriculture. The agricultural fertility changes have resulted from intensifying annual crop rotations from 1.5 to 2.5 crops and insufficient inputs. The removal of biomass from the forest has curtailed the natural organic cycle by virtually eliminating nutrient inputs.The soils are very acidic and have little C, N, P and exchangeable bases, but have large amounts of active iron. Basic nutrients are not sustained in agriculture and differences in inputs and management between irrigated and rainfed agricultural systems are becoming visible. Irrigated fields show the largest cation content because of input from irrigation water. Rainfed agricultural sites, which receive the most nutrients (fertilizers and manure), have the highest pH values and C and N contents. All soil fertility conditions are marginal and put into question the long‐term sustainability of current levels of production. Alterations in the cropping intensity are needed and the introduction of nitrogen fixing trees and crops seems to be the most viable option towards sustainabil

ISSN:0266-0032    

DOI:10.1111/j.1475-2743.1994.tb00474.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY