摘要:

Abstract.Using the simulation model MACRO, this paper investigates the likely consequences of reduced irrigation inputs on the water and salt balance and crop growth in a drained, saline clay in a Mediterranean climate (Marismas, SW Spain). The model was first successfully validated against field measurements of the soil water and chloride balance, water table depths and drain outflows in the 1989 growing season. Three‐year simulations were then performed assuming two different irrigation applications (60 and 75% reductions from the 1989 amount) and two different frequencies (12 or 6 irrigations per growing season). The model predictions suggested that reduced irrigation may lead to up to a 15%) increase in the chloride content of the soil profile after 3 years. Also, despite overall reductions in water discharge, slight increases in chloride leaching via field drains (c.4 to 8%) were predicted. The model demonstrated that encroachment of salt into the soil profile may he exacerbated by the non‐equilibrium nature of water flow and solute transport (‘by‐passing flow’) in structured clays. With reduced water supply for irrigation, more frequent applications may give marginally better crop yields for the same quantity of irrigation but at the expense of slightly increasing salt concentration in the

ISSN:0266-0032    

DOI:10.1111/j.1475-2743.1996.tb00530.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Abstract.Regular application of slurry manure in large quantities is thought to degrade soil structure and increase erodibility. One hypothesis links this to the large input of potassium which increases the exchangeable potassium percentage (EPP) and, thereby, dispersion. The effect of EPP on erodibility was quantified in three experiments. In the laboratory, eleven rainfall experiments were conducted using a silty topsoil from a typic Hapludalf which was fertilized to EPPs of 4 to 18%. Field rainfall experiments on 22 Inceptisols and Alfisols were used to examine whether the long‐term application of monovalent cations (Na+, K+and NH4+) with slurry manure had changed soil properties, especially erodibility. In addition, erodibilities of 32 soils determined with natural and simulated rains were taken from literature. The experiments on these 65 soils together covered a wide range of soils, slopes and rainfalls. Dispersion by a large percentage of highly hydrated ions (K+, Na+) reduced the infiltration rate faster, caused runoff up to 5 min earlier, and increased sediment concentrations by 15g/l compared to low EPP soils. These changes increased soil erodibility of the Universal Soil Loss Equation (USLE) by 0.021 t × h/N × ha (where N = Newtons) for each 1% increase in EPP + ESP (exchangeable sodium percentage). The ESP contributed little to this increase as ESP was less than 1/10 of EPP in the experiments.Fields with long‐term manure application had similar chemical, physical and microbiological soil properties as fields without slurry manure except for slightly greater pH (+ 0.6) and P (+ 17 mg/kg) values. We conclude that, as long as the potassium input and output are balanced, the long‐term use of slurry manure does not increase erod

ISSN:0266-0032    

DOI:10.1111/j.1475-2743.1996.tb00531.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Abstract.A model was developed to predict evapotranspiration and soil moisture changes, which could be used either for scheduling irrigation or crop water‐use studies. The general form of the model is reported here, and its validation for sugarbeet and potatoes is described in a subsequent paper. The soil characteristics required are depth of topsoil, texture or available water capacity of topsoil and subsoil, and whether a significant slope exists. The plant characteristics required are species and planting date. Meteorological data used to calculate potential evapotranspiration are obtained from the Meteorological Office synoptic network, but local rainfall data are preferred.The model estimates potential evapotranspiration of a reference crop, and uses this to model canopy and root development for all crops at each location. Available options allow for observed data on canopy or root development to be incorporated into the simulations. Estimates of potential evapotranspiration for each crop are then adjusted to allow for the effects of water stress, taking soil characteristics, root depth and evapotranspiration demand into account.The model enables growers to reduce the risks of under‐ or over‐watering their crops and has proved successful in irrigation manag

ISSN:0266-0032    

DOI:10.1111/j.1475-2743.1996.tb00532.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Abstract.A model was developed to estimate daily evapotranspiration and root zone soil moisture changes appropriate for scheduling irrigation, incorporating a modified version of the Penman‐Monteith equation.The model was field tested during 1992–94, for potatoes and sugarbeet, by comparing modelled root zone soil moisture changes with field measurements taken using neutron probes. The study confirmed the accuracy of the model when predicting crop water use and soil moisture change. Linear regression of measured versus modelled data exhibited a slope of 0.99 and an intercept close to and not significantly different from zero. The relationship accounted for 80% of the variat

ISSN:0266-0032    

DOI:10.1111/j.1475-2743.1996.tb00533.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Abstract.A land evaluation using unsophisticated data successfully predicted yield ranges of various crops in Burundi. Yields of wheat, pea, bean, maize and potato predicted from data for climate, soil and land use technology were compared with observed yields from farm trials and from seed station and research station trials. The predicted range of yield for each crop suitability class enclosed the mean farm yields 13 times out of 16 and yields on seed stations and research stations 10 times out of 15 and 14 times out of 21 respectively. The variability of the observed yields exceeded the predicted range of yields. The method is considered as validated. The method appears to be applicable for multi‐year studies at a broad scale, but yield variation according to the weather from year to year is not accounted for. The variances of the yields on farms are greater than the variances in seed station and research station trials.Since the method predicts correctly the mean regional farm yields, it could be useful for land use planning, research into optimal regional cropping specialisation, studies on food policy, and for evaluation of economic return and sustainability of different crop

ISSN:0266-0032    

DOI:10.1111/j.1475-2743.1996.tb00534.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Abstract.Soil microstructures and biological activity were studied in thin sections ofCullunaheathland soils subject to periodic burning. Freely drained Brown Podzolic soils from a species‐rich heath at Dinnet Muir, Aberdeenshire, Scotland were compared with shallow Humo‐ferric Podzols with a thick humus layer (5–10 cm) supporting a species‐poor heath at Balmenach, Aberdeenshire.Structures with greater porosity occurred in all Dinnet soils and the most recently burned Balmenach soil. Burning led to an increase in soil porosity which gradually disappeared after a period of 2–3 years. Soils of the recently burned site had more enchytraeid worms than those burned ten years previously. Most of the Dinnet soil samples were dominated by extremely fine granular structure which could have been produced by flocculation of well decomposed organic matter or by enchytraeid worms. In recently burned sites the increase in soil macro‐ and microbial activities may lead to the formation of composite structures.Regular burning every 10–15 years has been the land management practice in Scottish heathlands to ensure the production of fresh browse of nutritious heather shoots for herbivores. The near‐ground microclimate and regeneration mechanisms of heathland plants are well adjusted to the periodic disturbance by fire. We found that the gradual decrease in surface soil porosity over time can be restored by prescribed burning. Soil structure and the distribution and continuity of pores in the soil profile directly affect soil water movement and retention. These factors have important ecological implicationsforpost‐fire ve

ISSN:0266-0032    

DOI:10.1111/j.1475-2743.1996.tb00535.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Abstract.Usual residue‐management options are to remove the residue, use it as mulch with or without undercutting or to incorporate it into the soil. While the role of surface mulch in evaporation has been widely studied, the information on the effect on evaporation of mulch with undercutting or residue incorporated into soil, particularly in relation to soil type and evaporativity (Eo) is lacking. We studied the effect of wheat straw used in various ways on the course of evaporation loss from soil columns with three soils at Ludhiana, India and one soil at Bushland, Texas, USA, under two Eo's Energy‐limited evaporation rates under mulch (Eom) followed the soil‐specific relation Eom/Eo= a e(bRes+cEo), where Res is residue rate t/ha and a, b and c are constants; Eo, is expressed in mm/d. In an effort to model the total evaporation (CE) during the energy‐limited stage ‘U’ was obtained from appropriate CE versus time curves and (CE‐U) was regressed over (t ‐ ti)0.5to obtain the slope ‘α’ (Ritchie 1972) for the soil‐limited evaporation stage. The observed ‘U’ was independent of mulch rate and Eobut was strongly affected by soil type, Values of ‘α’ decreased with increase in mulch rate and decrease in Eoand coarseness of soil.The otherwise short lived benefit of evaporation reduction with mulchper se, which peaked after a few days was maintained when residue was mixed with soil at the stage when evaporation reduction reached a maximum; this benefit continued for several weeks. Cumulative evaporation values computed from ‘U’ and ‘α’ agreed closely with the observed values under straw mulch for loamy sand and clay loam soils and for ‘undercut’ and ‘residue mixed’ treatments on all soils regardless of Eo, and for all situations under small Eo. However, for sandy loam and silt loam soils under Eoof 10 mm/d, the modified square root of the time

ISSN:0266-0032    

DOI:10.1111/j.1475-2743.1996.tb00536.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Abstract.Simulated estimates of crop yield were made for rainfed rice in a 50 ha dryland rice area. The aim was to investigate how soil units and management units of different sizes with different yields could be used to obtain values for areas of land. Two procedures were applied. First, yields were simulated at six sites, that were representative of six soil mapping units. Second, yields were simulated using soil information from 133 auger sites, and were interpolated over management units using block kriging. Differences between the two procedures for the total area and for a test set of 22 additionally sampled locations were small. A 60% increase in precision was achieved when relatively large management units were defined.A Geographical Information System was used to identify areas with greatest yield potential for rainfed dryland rice. Statistical analysis showed that the six soil units could be grouped into three yield classes. The largest yields were obtained for a sub‐area comprising 11% of the survey area which was associated with a slowly permeable Bg horizon in the soil profile.It was concluded that the best procedure for the spatial interpolation of simulated rice yield should be based on preliminary simulation of crop yields. A sensitivity analysis of the impact of weather variability and soil heterogeneity on the variation of yield was useful to detect the importance of their contributions. The procedures developed in this study are of value in obtaining a reliable estimate of average yield, and can consequently be used for associated cost‐benefit calculati

ISSN:0266-0032    

DOI:10.1111/j.1475-2743.1996.tb00537.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Book reviews in this article:Soil Conservation and SilvicultureBy J. Dvořák&L. Novák (editors). Translated by V. Sochor.Environmental Soil Biology – 2nd EditionBy M.

ISSN:0266-0032    

DOI:10.1111/j.1475-2743.1996.tb00538.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY