Agronomy Journal 92:807 (2000)
© 2000 American Society of Agronomy
SPARSE CANOPY SYMPOSIUM INTRODUCTION
Water Relations of Sparse Canopied Crops
William A. Payne
Texas Agricultural Experiment Station, 6500 Amarillo Blvd. West, Amarillo, TX 79106 USA
w-payne{at}tamu.edu
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INTRODUCTION
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Most of the current theory on the relation between crop water use and yield has been developed for intensively managed crops with well-developed canopies. For example, in Tanner and Sinclair's (1983) discussion of biomass yield, T efficiency, and ET efficiency, a leaf area index (LAI) of at least 3 was assumed. In many developing countries, the agricultural inputs needed to obtain such LAI values are either unavailable or unaffordable. Crops are often sown at wide spacings in an attempt to avoid crop failure during drought, or to maximize use of low plant nutrient availability that is typical of the infertile soils often found in developing countries. In these subsistence agricultural systems, sparse canopied crops are the rule rather than the exception. Sparse canopies are also typical of some intensively managed crops, e.g., dryland cotton (Gossypium hirsutum L.) in developed countries.
Sparse canopied crops have characteristics that require re-examination of some of the assumptions commonly made for water relations of dense canopied crops. These characteristics include (i) mass and energy exchange, which is much more complex in sparse canopies than in dense ones, and (ii) physiological response of the crop to the canopy environment resulting from a sparse stand, or to the environmental stress that caused canopy sparseness in the first place. Obviously there could be feedback between the two types of physiological response.
In this symposium, which was held during the 1998 ASA meetings in Baltimore, several papers were presented with a view towards reviewing several aspects of water relations of sparse canopied crops. Of these, six are presented here. They discuss: (i) Yield/water use relations in sparse stands of pearl millet; (ii) The water and energy balance of sparse cotton crops, using a mechanistic simulation model that separately calculates soil and crop evaporation; (iii) The influence of soil type on the agronomic means available to increase water use efficiency (WUE) of rainfed crops; (iv) The effects of plant water status and canopy geometry on fluxes from sparse canopies and their understoreys; (v) An energy balance model, well suited for sparse-canopied surfaces, that was developed to use remotely sensed surface temperature to treat energy exchange from the soil and vegetation; and (vi) Convective transport due to the expansion of the soil air as it is warmed diurnally.
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REFERENCES
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- Tanner C.B., Sinclair T.R. Efficient water use in crop production: Research or re-search?. In: Taylor H.M., et al. , ed. Limitations to efficient water use in production. Madison, WI: ASA, CSSA, and SSSA, 1983:1-27.
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INTRODUCTION
REFERENCES
