Oswaldo Ernst1, Santiago Dogliotti2, Mónica Cadenazzi3, Armén Kemanian 4
1 Departamento de Producción Vegetal. Facultad de Agronomía, Universidad de la República, Ruta 3, km 363, Paysandú 60000, Uruguay, firstname.lastname@example.org
2 Departamento de Producción Vegetal. Facultad de Agronomía, Universidad de la República, Av. Garzón 780, 11200 Montevideo, Uruguay.
3 Departamento de Biometría, Estadística y Computación. Facultad de Agronomía, Universidad de la República, Ruta 3, km 363, Paysandú 60000, Uruguay.
4 Department of Plant Science, The Pennsylvania State University, 116 ASI Building, University Park, PA 16802, USA.
The increase in annually cropped area that has occurred in Uruguay since 2002 was largely achieved by converting crop-pasture rotations to continuous annual no-till cropping systems. We studied the impact of the number of years of continuous cropping after pasture (YCC) on wheat yield in 80 on farm-trials during three growing seasons comparing two nutrient managements: (1) “Limited by nutrient”, fertilised with N and P according to “best technical means”; (2) “Not limited by nutrients”, adding ‘not limiting’ amounts of N, P, K and S. We estimated the frontier yield under limiting (Y–) and non-limiting nutrient supply (Y+) using a stochastic frontier production function. Y+ after perennial pasture was 8.42 vs 7.04 Mg ha-1 of Y–. While Y– was reduced 0.12 Mg ha-1 year-1 from YCC=1 to YCC=10 (P≤0.05), Y+ was maintained at the same level till YCC=5 and then reduced by 0.18 Mg ha-1 year-1 (P≤0.05). Total yield reduction after 10 years of continuous cropping, measured as Y+ at YCC=1 minus Y– at YCC=10, was 2.55 Mg ha-1, representing a relative yield gap of 30.4. Soil quality deterioration explained up to 40% of this yield difference. Reduced soil nutrient supply capacity, partially quantified as potentially mineralisable nitrogen (PMN), would be the soil property most limiting Y– during a period of 4-5 years after pasture. When YCC>5, a negative effect of YCC on frontier yield could not be compensated by increased nutrient application rates. We identify reduced soil infiltration rates as a soil property that may explain Y+ reduction after 5 YCC.