A method of energy balancing in crop production and its application in a long-term fertilizer trial

Data of a 32-year field experiment (1967-1998), conducted on a fertile sand y loess in the Hercynian dry region of central Germany, were used to (i) de monstrate the methodological basis of energy balancing in a long-term trial and (ii) identify time trends of various energetic parameters, as affected by the rate and form of nitrogen (N) application. Of the 16 fertilizer reg imes, 5 were selected to represent the broad range of N supply conditions: no N, mineral N only, farmyard manure N only, high input of both mineral an d farmyard manure N, and moderate input of the two forms of N. The crop rot ation included various cereals, sugar beets, and potatoes. In calculating t he energy balances, changes in soil and crop husbandry practices over the p ast decades were taken into account. The input of energy associated with mi neral N fertilization declined markedly with duration of the experiment, wh ereas the input of energy associated with chemical plant protection increas ed. The input of energy was highly variable; it ranged from 8.9 to 36.9 GJ ha(-1) per year in the last crop rotation, depending on the N regime and th e crop. Because of the high soil fertility, the average biomass yield of al l the crops grown within a rotation was as high per year. On the fertilized plots, net as 13.5 t dry matter (DM) ha(-1) per year; the output of energy was as high as 215 GJ ha(-1) energy output (energy content of the grains m inus energy input) and energy utilization improved with time. Winter wheat, fertilized with moderate amounts of mineral and farmyard manure N, showed an increase in net energy output of 86% from 1972 to 1995. During the same period, the energy intensity (input of fossil energy per grain equivalent) declined by 45%, and the output/input ratio increased by 67%. In part, thes e trends can be attributed to the higher grain yield (+59%). Energy output and net energy output are the crucial parameters when the demand for plant products cannot be met because of the limited area for growing crops. Energ y intensity and energy output/input ratio are integrative indicators of the environmental effects of crop production, which can be used to formulate r ecommendations for fertilization, which are optimum as far as the environme nt is concerned. (C) 2001 Elsevier Science B.V. All rights reserved.