摘要:

Abstract.A simple model for droughtiness, when linked to the distribution of soil types in England and Wales, is potentially valuable for estimating drought‐induced losses of yield in winter wheat at either particular places or in larger areas of the country. The model defines droughtiness,D, in terms of the soil water extractable by the crop,AP, and the adjusted potential moisture deficit,MD:D=AP−MD.The model should represent well the growth of actual crops of winter wheat ifAP, which is based on laboratory measurements, accurately simulates the extraction of soil water by roots, ifMDrepresents the cumulative transpiration of water by wheat crops by mid‐July, and if the latter is an appropriate date for testing the effect of drought on grain growth. These three assumptions have been investigated using measurements of artificially draughted crops of winter wheat.The results indicate that mid‐July is a good choice for a single date andMDa good representation of the water requirement of a wheat crop that has been draughted to the point where yield is beginning to be affected. For the deep‐rooting crops studied,APunderestimates the soil water extracted by the crop, and therefore overestimates the susceptibility of the soil to droughtIf averageMDvalues are replaced by means and a standard deviation the resulting normal distribution ofD‐values can be used to assess the probability that drought will limit yields. When applied to a droughtiness map of England and Wales withAP‐values used for the soils the model predicts that the soils growing wheat will be susceptible to drought in 16–84 years out of every 100. Our results suggest, however, that this probably applies to shallow rooting or diseased crops and that for deep‐rooting, healthy crops the drought risk is

ISSN:0266-0032    

DOI:10.1111/j.1475-2743.1988.tb00733.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Abstract.Research on soil erosion under forest in Britain is reviewed. Erosion can increase as a result of afforestation in the uplands, sometimes with undesirable consequences for surface water quality. Published rates of erosion are usually close to ‘natural’ ones, at around 500 kg ha−1yr−1. Of the forest operations that can lead to erosion ploughing is the most important. Clearfelling may also increase erosion, but little is known of its long‐term effects. New developments in forestry may do much to reduce the risk of soil erosion, particularly the replacement of ploughing by subsoiling and the control of drain

ISSN:0266-0032    

DOI:10.1111/j.1475-2743.1988.tb00734.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Abstract.The experiment conducted jointly by the Forestry Commission (FC) and the Institute of Terrestrial Ecology (ITE) at Beddgelert Forest, North Wales, studies the effect of conventional clear‐felling (CF) and whole‐tree harvesting (WTH) of Sitka spruce (Picea sitchensis) on the local ecosystem and on the future productivity of forestry at the site. Bulked soil samples were taken from Block 2 of the experiment just before felling in 1984 and two years later in 1986. Sub‐samples from the horizons Ah, E and B+C were analysed for exchangeable and short‐ and long‐term reserves of K using Ca‐resin and strong acid extraction procedures. The flux of K through the soil profile after both CF and WTH resulted in a small increase in exchangeable K throughout the profile after both treatments, but in a loss of short‐term reserves from the surface Ahhorizons of both and an overall loss of these after WTH. The nutrient flux down‐slope through the Ahhorizon could result in differential nutrient deficiency in future. The data suggest that exchangeable and short‐term reserves of K will support about two further cycles of conifers, with either CF or WTH, but that long‐term reserves are likely to be released quickly enough to meet the needs of such a slow‐growing crop; these would support about 30 cycles. Other nutrients, such as Ca or P, may prove to be

ISSN:0266-0032    

DOI:10.1111/j.1475-2743.1988.tb00735.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Abstract.Ploughing and tine cultivation to depths of 5, 15 and 25 cm were used to prepare land before sowing winter wheat. The methods were compared for two years with or without the presence of straw residues from the previous crop and the effects on crop growth and yield were assessed.Some combinations produced large differences in yield. In 1985–86 volunteer cereals were a problem where straw was not burnt, but deeper ploughing controlled them. In both years the concentrations and uptake of nitrogen, phosphorus and potassium differed during the early period of growth but not at maturit

ISSN:0266-0032    

DOI:10.1111/j.1475-2743.1988.tb00736.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Abstract.The effect of eight years of applications of five rates (0, 134, 269, 538 and 1075 m3ha−1a−1) of pig slurry on the soil strength two years later were studied in a field experiment. Soil strength in the 0–150 mm depth was measured on five occasions in winter using a hand‐held recording cone penetrometer. On one occasion the penetration resistance at some depths greater than 100 mm was significantly (P<0.001) decreased by adding more than 269 m3of slurry ha−1a−1. On three occasions different amounts of slurry caused significant differences in the rate of increase of penetration resistance with depth. Large applications of slurry may decrease penetration resistance because they increase organic matter, thereby increasing the water retention

ISSN:0266-0032    

DOI:10.1111/j.1475-2743.1988.tb00737.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY