On crop production and the balance of available resources

One of the main insights achieved in the early days of agricultural science is that each environment has a specific balance of resources, which is ava ilable to the crop. This balance determines crop production, the effect of resource addition and the effect of agronomic operations. However, attempts to quantify this balance are scarce. It is normally taken into account ind irectly by a general description of soil, climate, topography, land use his tory, etc. This paper advocates quantifying this balance by quantification of the degree of limitation of resources. A coefficient (between zero and o ne) is developed which implements this idea. The paper shows that under a m oderate assumption, the sum of the limitation coefficients of all resources equals one. This makes the deduction possible of non-limiting resources. T he original binary concept of limitation can be regarded as a special case of this coefficient. The paper shows that crop response to addition of a re source can be viewed as the product of: the limitation coefficient, the use efficiency, and the amount of the dose. General crop production principles as the law of diminishing returns and the law of the optimum can be interp reted easily this way. Methods to estimate experimentally the limitation co efficients an discussed. The methods are illustrated by estimating the degr ee of limitation of nitrogen and phosphorus in southwest Niger. These two e lements account for more than 70% of the total limitation (of carbon dioxid e, radiation, water, and all nutrients), which is in agreement with other s cientists in this region who indicate these two elements as the 'principal' limiting factors. (C) 2000 Elsevier Science B.V. All rights reserved.