VALIDITY OF ROTATION AS AN EFFECTIVE AGROECOLOGICAL PRINCIPLE FOR A SUSTAINABLE AGRICULTURE

Agriculture in industrialized countries is based on specialized agroecosystems, where high yields are obtained from sequences of annual crops (cash crops) with large inputs of chemicals. A sustainable agriculture should conversely rely on major exploitation of native resources, i.e. sun energy, water from precipitations, atmospheric nitrogen, soil organic matter. Crop rotation, based on the inclusion of polyannual legumes, is to be considered among the most powerful management practices for pursuing such aims because of its implications for maintaining soil fertility, saving energy and avoiding pollution. Results confirming the validity of this statement are presented. The residual effect on the succeeding crop (sunflower) of a long-term rotation, which included a four-year lucerne ley, in comparison with a sequence of annual crops, was investigated in a mediterranean environment (Central Italy). Similar yields were obtained in very contrasting conditions. Approximately up to 3000 kg ha-1 seed yield and 1400 kg ha-1 oil yield were recorded either with lucerne as the preceding crop, without any addition of inorganic-N and with mechanical weed control, or with safflower as the preceding crop, supplying sunflower with 130 kg ha-1 of inorganic-N and chemical weed control. The effects of the treatments on yield are also discussed.