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  • 1
    Electronic Resource
    Electronic Resource
    Dynamic model for the effects of K fertilizer on crop growth, K-uptake and soil-K in arable cropping. 2. Field test of the model (1997)
    Oxford, UK : Blackwell Publishing Ltd
    Soil use and management 13 (1997), S. 0 
    Details
    ISSN: 1475-2743
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract. The validity of the model described in Greenwood & Karpinets (1997) was tested against the results of single year, multi level K fertilizer experiments. Measurements of plant mass, %K in the plant and K activity ratio in soil had been made at harvest and at intervals during the growing season on spring wheat, summer cabbage and turnips. Reasonably good agreement was obtained between these measurements and simulated values when the two ‘crop’ parameters (defining the dependence of critical and maximum possible %K on plant mass) were adjusted for each crop. Also good agreement was generally obtained for plant weight and plant %K at harvest in less detailed experiments on 10 other crops. Values of the two ‘crop’ parameters for 12 of the crops were strongly correlated with one another suggesting that a single ‘crop’ parameter may be all that is required to define most inter-species differences in plant-K demand.Simulations with the model indicate that, in central England, no response of 10 crops to K fertilizer would be likely on soils containing more than 170 mg of 1 M ammonium nitrate extractable-K/kg of soil and having clay contents of between 15 and 45%. Shortcomings of the model and opportunities for advance are discussed.A simplified version of the model runs on the Internet at:
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1475-2743.1997.tb00583.x
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  • 2
    Electronic Resource
    Electronic Resource
    Dynamic model for the effects of K-fertilizer on crop growth, K-uptake and soil-K in arable cropping. 1. Description of the model (1997)
    Oxford, UK : Blackwell Publishing Ltd
    Soil use and management 13 (1997), S. 0 
    Details
    ISSN: 1475-2743
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract. To provide a practical aid to improving fertilizer practice a mechanistic model was developed that can be readily calibrated for widely different crops. Most of the inputs are easy to obtain and the others, the amounts of fixed soil-K and the velocity constants for fixation and release of soil-K, can be readily measured by a novel procedure which is described.The model calculates for each day the potential increase in plant weight and the increment in root length, from the current plant mass, its %K and pan evaporation. It calculates the maximum amount of K that could be transported through soil to the root surfaces. It modifies this potential uptake by taking account of the ‘feedback’ of plant K on root absorption to give the actual uptake and a new %K in the plant. It calculates the radii of the depletion zones around each root increment and the interchange between the solution, exchangeable and fixed-K in these zones and also in the undepleted regions of soil. Routines are included for the effects of weather on the various processes. Differences between species are accommodated by selecting one of three algorithms for root growth and by adjusting the values of two crop-K parameters that define the decline in a critical and a maximum possible %K with increase in plant mass per unit area.A simplified version of the model runs interactively on the Internet at:
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1475-2743.1997.tb00582.x
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  • 3
    Electronic Resource
    Electronic Resource
    Aerobic Respiration in Soil Crumbs (1962)
    [s.l.] : Nature Publishing Group
    Nature 195 (1962), S. 161-163 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] IN previous work1 a theory was developed to relate the aerobic respiration-rates of spherical soil crumbs to their size and the oxygen partial pressure surrounding them. The object of this communication is to correct an error in the formulation of the theory and to extend it to describe the ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/195161a0
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  • 4
    Electronic Resource
    Electronic Resource
    Quantitative relationships for the dependence of growth rate of arable crops on their nitrogen content, dry weight and aerial environment (1986)
    Springer
    Plant and soil 91 (1986), S. 281-301 
    Details
    ISSN: 1573-5036
    Keywords: Cereals ; Critical concentration ; Models ; Nitrogen stress ; Plant-N content ; Potatoes ; Quantitative relationships ; Radiation ; Simulation ; Vegetables
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Quantitative relationships for growth rate and its dependence on plant nitrogen concentration are developed from the results of experiments on potatoes, cereals and vegetables. The relationships appear to be of general applicability and most coefficients in them are similar for widely different crops. It is argued that during the main growing period (May–August inclusive) in Western Europe growth of crop dry matter may be limited by self regulatory mechanisms within the plant and is little affected by variations in the aerial environment when there is ample water and nutrients. Under these conditions both growth rate and the critical % N in the dry matter (the minimum % N at which growth rate is maximum) are simple functions of plant dry weight. It is deduced that when account is taken of the effect of plant weight on % N in the dry matter, growth rate is, as a close approximation, linearly related to % N until this reaches the critical value and constant at higher values. A computer simulation model based on these relationships enabled estimates to be made of the influence of measured plant-N concentrations on the increase, throughout the season, in the dry weight of potatoes and cereals grown with different levels of N fertilizer. There was good agreement between the estimates made in this way and the results of numerous field experiments.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02198111
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  • 5
    Electronic Resource
    Electronic Resource
    Dependence of soil mineral N on N-fertilizer application (1986)
    Springer
    Plant and soil 91 (1986), S. 417-420 
    Details
    ISSN: 1573-5036
    Keywords: Fertilizer nitrogen ; Nitrogen loss ; Potatoes ; Soil mineral nitrogen
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary The extent to which fertilizer N applied to soil could be recovered by conventional soil analysis for mineral N was studied in 15 N-fertilizer experiments on potatoes. In seven of them up to 85% of the fertilizer N apparently disappeared and then reappeared during the subsequent five weeks. When “disappearance” was plotted against time from fertilizer application the points fitted approximately about the same curve despite the soils differing widely in organic-matter content, pH and texture. It appears that soil sampling for giving advice on fertilizer-N levels should be delayed for a substantial period after an application of fertilizer N.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02198135
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  • 6
    Electronic Resource
    Electronic Resource
    Response of potatoes to N fertilizer: Dynamic model (1985)
    Springer
    Plant and soil 85 (1985), S. 185-203 
    Details
    ISSN: 1573-5036
    Keywords: Fertilizer experiments ; Soil mineral N ; Simulation model ; N content ; N response ; Potatoes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary A simulation model is described to interpret N fertilizer experiments on potatoes. It calculates the total growth of dry matter, the N uptake, the partition of dry matter and of N between tuber and foliage and the distribution of inorganic N down the profile for each day during the growing season. The validity of the model was tested against measurements of these parameters made at approximately fortnightly intervals on plots that received N fertilizer and those that received none in 4 experiments on a sand, 4 on a sandy loam and 3 on a clay soil. Simulated values were in reasonably good agreement with the measured values in all experiments. Overall the sums of squares of the differences between the simulated and measured values of the %N in the total plant, and the total amount of inorganic N in the top metre of soil and the logarithms of the total weight of dry matter, tuber dry weight, N uptake in the entire plant and N uptake in the tubers were each less than 25% of the sum of squares of the measured values about the mean. Only 9 inputs were required for the model. It was found essential to take account of differences in spring and summer leaching but not of inter-site differences in mineralization rate.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02139623
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  • 7
    Electronic Resource
    Electronic Resource
    Response of potatoes to N fertilizer: Quantitative relations for components of growth (1985)
    Springer
    Plant and soil 85 (1985), S. 163-183 
    Details
    ISSN: 1573-5036
    Keywords: Growth rate ; N content ; Mineralization ; N uptake ; Assimilate partition
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Quantitative relationships for key processes influencing N response were derived from measurements of inorganic N in soil, the weights and N contents of foliage and tubers made at intervals during growth of maincrop potatoes in 11 N fertilizer experiments. Apparent mineralization rates (calculated from measurements of N uptake and inorganic N in the top metre and averaged over the growth period) were remarkably similar from site to site despite wide differences in the textures, water contents and organic matter contents of the soils. They were mostly about 0.78 kg N ha−1 m−1 d−1. Inorganic N in the top 50 cm of soil was rapidly removed by the crop until it fell on all sites to a low value (about 4 μg N cm−3) which was maintained for the remainder of the growth period. When N fertilizer was applied, growth rate until at least the end of July was always well defined by a single coefficient in a previously derived equation. Average values of this coefficient for each of the soil types and for each of the years in which the experiments were carried out were within 20% of each other. The minimum %N in the dry matter needed to permit maximum growth rate declined with increase in plant weight in a similar manner to that previously found for other crops. Equations were found for the partition of assimilate and of nitrogen between the foliage and tubers. The coefficients in them were little affected by whether or not N fertilizer was applied. According to these relationships the maximum potential dry weight yield of tubers is 20 t ha−1 and requires the crop to contain at least 290 kg N ha−1.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02139622
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  • 8
    Electronic Resource
    Electronic Resource
    Quantitative relationships for growth and N content of different vegetable crops grown with and without ample fertilizer-N on the same soil (1988)
    Springer
    Nutrient cycling in agroecosystems 18 (1988), S. 175-188 
    Details
    ISSN: 1573-0867
    Keywords: N-response ; critical % N ; recovery ; mineralization rate ; vegetables ; inter-species variability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Unexpected relationships were found to cover various features of N-response of 12 different crops grown in 26 experiments on adjacent sites in the same field. When N-fertilizer was withheld the % N in the dry matter of the different crops declined in a regular way with increasing plant weight and was always about 0.6 × the critical % N; crop weight was approximately proportional to the weight with ample fertilizer and the constant of proportionality was also about 0.6. For drilled crops, the maximum plant dry weight obtained with any level of fertilizer-N was almost linearly related to the duration of growth. These results are in approximate agreement with those predicted with a previously described simulation model. On the basis of this work, a simple field method is suggested for estimating the rate of mineralization of soil organic matter in some soils. The apparent recovery of fertilizer-N by the different vegetable crops always declined linearly with increase in fertilizer-N over the entire range of applications which is in marked contrast to the constancy of apparent recovery by crops like cereals and grass that have more extensive root systems. In some instances, the apparent recovery of the vegetable crops also declined linearly with increase in the % N in the plant dry matter. The apparent recovery of an infinitely small amount of fertilizer-N by the different crops, when plotted against plant weight fell approximately about the same ‘diminishing returns’ type curve. The implications of these findings to the further improvement of the model are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01049512
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  • 9
    Electronic Resource
    Electronic Resource
    Experimental validation of an N-response model for widely different crops (1988)
    Springer
    Nutrient cycling in agroecosystems 18 (1988), S. 153-174 
    Details
    ISSN: 1573-0867
    Keywords: Simulation ; yield ; N-content ; vegetables ; inter-species variation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract A simulation model, developed from a previously published one generally gave a reasonably good description of the effects of N-fertilizer on plant dry weight and N-content of 12 different vegetable crops grown in 26 experiments on separate sites within the same field. Apart from standard weather and soil data, the model required as inputs, the maximum yield of dry matter, the fractional recovery of N by the crop (with minimum fertilizer), the plant mass and N content (at the time of planting or drilling), the dates of planting or drilling and of harvest. Simulations always started from the previous autumn. A constant value of soil mineral-N at that time and the same temperature dependent mineralization was assumed for all experiments. The validity of the model was tested by a range of statistical procedures. In 19 out of the 26 experiments there were no detectable trends in the deviations of the simulated from the measured dry matter yields with increase in fertilizer-N. The model over-estimated the %N in the dry matter of some crops at the highest level of fertilizer-N and was unsatisfactory for one of the crops. With these exceptions, the sum of squares of the differences between measured and simulated %N was 22% of the sum of squares of the measured values above the mean. When N-fertilizer was withheld, the average N-uptake over all experiments was 69 kg N ha−1, whereas that simulated was 59 kg N ha−1; the average difference between simulated and measured uptake for each experiment was 20 kg N ha−1. Simplification of the model by incorporating the same relationship between critical %N and plant weight for all crops did not lead to appreciable loss of accuracy. A user-friendly version of the model has been compiled so that it will run on IBM-compatible microcomputers with outputs that can be coupled with high level graphics packages.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01049511
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  • 10
    Electronic Resource
    Electronic Resource
    Fertilizer use and food production: World scene (1981)
    Springer
    Nutrient cycling in agroecosystems 2 (1981), S. 33-51 
    Details
    ISSN: 1573-0867
    Keywords: energy ; models ; N-fixation ; nutrients ; re-cycling ; yield ; food production
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Cereal yield per ha in the different countries of the world is almost proportional to the rate of fertilizer application. Yields in countries where most people live are severely limited by nutrient deficiencies. Unless steps are taken to rectify these deficiencies, crop yields will always be very poor, even if other improved agronomic practices are adopted. Much fertilizer is at present wasted because of difficulties in forecasting how to adjust levels and methods of application for differences in conditions. More widespread adoption of ‘mechanistic’ approaches to studying the problems than hitherto offers opportunities for improvement. Considerable scope also exists for saving fertilizer by more re-cycling of nutrients, by greater biological-N fixation and by the adoption of better cropping sequences. Only a minute fraction of the present consumption of fossil energy in the world is needed to manufacture all the required fertilizer. Adequate supplies of potassium and phosphate minerals probably exist to meet demand. The major problems in the future are likely to arise from the fact that essential resources are very unevenly distributed in relation to where they are needed to grow food.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01072876
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