Intensification of agriculture in the south-eastern Pampas: I. Capture and efficiency in the use of water and radiation in double-cropped wheat-soybean

Abstract

The production of dry matter and grain depends on the ability of crops to capture resources. On an annual basis, farming systems centred on single crops waste large proportions of key inputs including incoming solar radiation and rainfall. Intensive farming involving multiple crops per year could improve resource capture and productivity. Resource productivity is defined as the ratio between output (biomass or grain yield) and annual input of photosynthetically active radiation (PAR) or rainfall. This paper tested the hypotheses that (i) wheat-soybean (Triticum aestivum L. and Glycine max (L.) Merr., respectively) double cropping increases resource productivity in relation to single crops through improved capture and efficiency in the use of resources, and (ii) the link between radiation- (RUE) and water-use efficiency (WUE) previously established for sole crops remain when scaling up to double cropping. Sequential and relay wheat-soybean double crops were compared with sole crops during 2 years in the south-eastern Pampas of Argentina. Water and radiation productivity (RP) were analysed as the product between proportion of resources captured by crops and the efficiency in the use of resources to produce plant material, i.e. RUE, and WUE. Responses of resource productivity to cropping strategy were generally similar for dry matter and grain yield. Differences between sequential and relay wheat-soybean double crops were minor. On an annual basis (i.e. from 1 May to 30 April), both water and RP were higher in double crops than in sole crops. This was largely related to improved capture of resources. On a seasonal basis (i.e. from sowing to physiological maturity), however, double and sole crops had similar water productivity whereas RP was lower for double crops, intermediate for soybean and higher for wheat. The impact of double cropping on resource capture was much larger for water than for radiation. The fraction of annual precipitation captured by crops increased from 0.26 to 0.51 in sole crops to 0.53 to 0.71 in double crops, whereas the capture of annual PAR increased from 0.24 to 0.31 to 0.38 to 0.44. The differential impact of double cropping on the capture of resources reflects the difference between storable (water) and non-storable resources (radiation). In agreement with our proposition, water use efficiency was closely associated with radiation use efficiency. For our conditions, further improvement in farming systems based on multiple cropping should target practices to enhance capture of radiation. © 2003 Elsevier B.V. All rights reserved.