Wheat yield gap

Soil quality depletion as determining factor: Doctoral thesis abstract

Abstract

During the last 50 years, food production was sustained by intensive use of energy in mechanization and agrochemicals, and cultivars with high response to nitrogen (N). This procces generated negative impacts on soil and water quality, increasing greenhouse gas emissions. Food, fiber and energy increase for coming years requires new strategies, capable to reduce yield gap (Yg), increasing input and resource use efficiency, but contributing to natural resources conservation. We studied the impact of agricultural intensification process, defined as years of continuous cropping (YCC), on attainable wheat yield (Yatt) and Yg, (difference between Yatt and actual yield. We use three different approaches: i) quantifying YCC effect on soil productivity evolution in the short term (i.e. <10 years) using wheat Yatt derived from five-year producers’ records; ii) studying soil properties underlining the response of wheat yield to YCC in 80 on-farm trials under limited and no limited nutrient supply; iii) comparing different cropping systems (CS) under three N levels (N0, N80 and N190 kg ha-1 ) in a long term experiment. Our results show a negative effect of YCC on Yatt particularly under unfavorable environmental conditions for wheat production. Two processes are associated to YCC effects: a) reduced soil nutrient supply capacity; b) yield reduction due to other soil properties than nutrient supply capacity depletion, related to the soil physical properties. The first one operates for YCC≤5, generating a Yg attributable to nutrients. The second limits the Yalc generating Yg not attributable to nutrients supply, that reached 40% for YCC=10. Crop-pasture rotation under no-till determined the lowest Yg, associated to better soil quality indicators. Including high frequency of grain sorghum and maize under continuos no-till, we obtained similar Yatt that rotating with pasture, but increasing Yg attributable to nutrients supply. Based on our results, we discuss the sustainability of intensification process of agriculture operated in the last 20 years in this region.