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  • 1
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    The effect of sowing date and season on the development and yield of Navy beans (Phaseolus vulgaris) in south-east England (1976)
    Cambridge University Press
    Details
    Publication Date: 1976-02-01
    Description: SUMMARYThe results of experiments in which Navy beans (cv. Purley King) were precision drilled at the beginning, middle and end of May in 1972, 1973 and 1974 suggest that the optimum time to sow is mid-May when soil temperatures at 10 cm depth have reached 12–13 °C. Earlier sowing usually led to a reduced plant stand and low yields whilst in 1972 and 1974, two exceptionally cool years, later sowing resulted in lower yields following a reduction in 1000-seed weight.Despite contrasting weather conditions acceptable yields of seed were obtained in all 3 years from mid-May sowings although cool wet conditions in the autumn of 1974 curtailed drying of the seeds below 30% moisture content. Accumulated temperatures (Ontario units) were successfully used to predict stages in crop development and the data used to demarcate the areas in England most suitable for Navy-bean production.
    Print ISSN: 0021-8596
    Electronic ISSN: 1469-5146
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Published by Cambridge University Press
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  • 2
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    An evaluation of the minirhizotron technique for estimating root distribution in potatoes (1991)
    Cambridge University Press
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    Publication Date: 1991-06-01
    Description: SUMMARYThe minirhizotron technique was evaluated for estimating root length density in potatoes (Solanum tuberosum ‘Record’) by comparing observations in angled 45° glass tubes with corresponding root length densities obtained by (a) destructive core sampling, and from (b) counts of root tips on the soil face of excavated trenches. Measurements were made in a field experiment in Bedfordshire, UK, in 1985, with shallow and deep cultivation as variables, and in a glasshouse trial.Only at depths below 0·3 m did root lengths observed with minirhizotrons reflect at all closely those estimated from core sampling and even then there was a tendency to overestimate root density. In the surface cultivated layers, where 80–90% of the total root length was present, results from minirhizotrons were unreliable, probably because of poor soil–tube contact and, in soils which shrink on drying, preferential root growth at the interface between the soil and the glass.Minirhizotrons can provide a realistic estimate of the rate of root growth of potatoes with depth over time when compared with maximum depths of water extraction, but appear to be unreliable for providing a quantitative measure of total root length density.
    Print ISSN: 0021-8596
    Electronic ISSN: 1469-5146
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Published by Cambridge University Press
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  • 3
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    Changes in the water status of tea clones during dry weather in Kenya (1977)
    Cambridge University Press
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    Publication Date: 1977-10-01
    Description: SummaryPartial closure of the stomata occurred during the middle of the day even when tea plants were growing in a wet soil and there were similar diurnal changes in the xylem water potential (ψx). As the soil dried the daily minimum values of ψx declined, more in some clones than in others, and there were also interesting differences between clones in the sensitivity of their stomata to changes in ψx. Possible ways in which these observations could form the basis of tests for screening clones for drought resistance are discussed.
    Print ISSN: 0021-8596
    Electronic ISSN: 1469-5146
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Published by Cambridge University Press
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  • 4
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    Crop production and water-use. III. The development and validation of a water-use model for potatoes (1994)
    Cambridge University Press
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    Publication Date: 1994-12-01
    Description: SUMMARYAs a prerequisite for developing crop-yield/water-use functions for potatoes using the results of historical irrigation experiments, it was necessary to develop a water-use model which could operate with a limited data set. The general form of this model has been reported by Wright et al. (1994), and its application to the sugarbeet crop by Hamer et al. (1994). In this paper the development and validation of the model for potatoes is described.The canopy was modelled in terms of intercepted incoming solar radiation using functions based on thermal time and time. Four phases of growth were identified: emergence, expansion, plateau and senescence. An empirical drought factor was included to allow for the effects of water stress on canopy development during the expansion phase. Root development was described using a two-phase model: linear and maximum depth (both time dependent).Independent data from various sources were then used to validate the model in terms of its capacity to predict crop canopy development, with and without drought stress, soil water extraction at different depths and soil water deficits during the season. The study confirmed the validity of the model for predicting the water-use of potatoes.
    Print ISSN: 0021-8596
    Electronic ISSN: 1469-5146
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Published by Cambridge University Press
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  • 5
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    Crop production and water-use. II. The development and validation of a water-use model for sugarbeet (1994)
    Cambridge University Press
    Details
    Publication Date: 1994-08-01
    Description: SummaryAs a prerequisite for developing crop-yield/water-use functions for sugarbeet using the results of historical irrigation experiments, it was necessary to develop a water-use model which could operate with a limited data set. The general form of this model has been reported by Wright et al. (1994). In this paper the development and validation of the model for the sugarbeet crop is described.The canopy was modelled in terms of the leaf area index and the relative interception of incoming solar radiation using functions based on thermal time and time. Four phases of growth were identified: emergence, slow-growth, fast-growth and full-canopy. An empirical drought factor was included to allow for the effects of water stress on canopy development during the slow- and fastgrowth expansion phases. Root development was described using a three phase model: initial (temperature dependent), linear and maximum depth (both time dependent).Independent data previously reported from Broom's Barn Experimental Station were then used to validate the model in terms of its capacity to predict crop canopy development, with and without drought stress, soil water extraction at different depths and soil water deficits during the season. The study confirmed the validity of the model for predicting the water-use of sugarbeet.
    Print ISSN: 0021-8596
    Electronic ISSN: 1469-5146
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Published by Cambridge University Press
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  • 6
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    Crop production and water-use. IV. Yield functions for sugarbeet (1997)
    Cambridge University Press
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    Publication Date: 1997-08-01
    Description: The water-use model (watyield) was used to estimate a number of variables which were then related to the actual yields recorded in long term sugarbeet experiments carried out at several sites in England over the last 30–40 years. Nine functions were developed which are based on yield/water-input, yield/crop evaporation and (the equivalent of) relative yield/relative crop evaporation relationships. In all cases, highly significant linear correlations were obtained but the levels of precision, and degree of site specificity, varied. For irrigation planning and water allocation, three approaches are recommended with increasing sophistication and, in general, precision. These are (1) relating yield increases to the estimated irrigation need; (2) relating actual yields to crop evaporation totals; and (3) determining actual yields for rainfed and irrigated crops from the calculated seasonal totals of the ‘effective’ solar radiation intercepted by the crop canopy. These values can be estimated with the model using standard weather and soil physical data appropriate to the locality and the crop.
    Print ISSN: 0021-8596
    Electronic ISSN: 1469-5146
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Published by Cambridge University Press
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  • 7
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    Irrigating seedling tea in Southern Tanzania: effects on total yields, distribution of yield and water use (1974)
    Cambridge University Press
    Details
    Publication Date: 1974-10-01
    Description: SUMMARYIn a dry area of Southern Tanzania with a single rainy season irrigation during the six-month-long dry season (May-November) doubled the total annual yield of tea and at the same time evened its distribution over the year to some extent. Other factors including low temperatures limited growth rates during the period June-September despite irrigation, whilst a lull in production in November appeared to be unrelated to external factors. Roots were traced to depths of about 4·3 m and by the end of the dry season unirrigated bushes were drying the soil below 3m. In general total yields decreased with decreasing frequency of irrigation and quantity of water applied but because these plants were deep rooting they could withstand deficits up to 100 mm without a reduction in yield, equivalent to a loss of about 25% of the total available water in the profile. There was some evidence that the most economical use of water occurred when the soil was not rewetted to field capacity at each irrigation, although yields were then less. Irrigation also reduced the incidence of a stem canker, Phomopsis theae. The implications of these results to the tea industry of East Africa are discussed.
    Print ISSN: 0021-8596
    Electronic ISSN: 1469-5146
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Published by Cambridge University Press
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  • 8
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    Crop production and water-use. I. A model for estimating crop water-use with limited data (1994)
    Cambridge University Press
    Details
    Publication Date: 1994-08-01
    Description: SummaryAn attempt was made to re-assess the results of irrigation experiments carried out in the UK during the last 30–40 years in order to develop functional relationships between crop yield and actual wateruse. It was first necessary to develop a model, based on relatively simple functions, which could be used to predict actual water-use (evaporation and transpiration). The derivation of this model, known as WATYIELD, is reported here, whilst its application and validation for sugarbeet and for potatoes are described in subsequent papers. Simple functions relate components of evaporation to the proportion of the incoming solar radiation intercepted by the crop canopy, reference crop evapotranspiration, the precipitation and irrigation amounts and the soil water deficit. Transpiration is also related to soil hydraulic characteristics, rooting density and potential evaporation rate.
    Print ISSN: 0021-8596
    Electronic ISSN: 1469-5146
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Published by Cambridge University Press
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