Medium-term fertilization strategies on extensive grain cropping systems under water table influence

Abstract

CONTEXT: Historical increases in grain yields have been associated with an undermining of soil organic matter (SOM) and a reduction of nutrient cycling capacity. Nutrient limitations for grain crop production are ubiquitous, and while yield and economic response to fertilization has been exhaustively evaluated on several crops across different environments, the focus has been mainly on individual crops rather than on the cropping system. Benefits of increased fertilization beyond a single cropping season need to be assessed to help preventing the current soil nutrient mining process in the Argentine Pampas. OBJECTIVES: i) Evaluate the effect of different fertilization strategies over crop yields across rotation cycles and locations (and their interactions); ii) determine the relationship between crop yield response to fertilization and the physical and chemical soil variables; iii) evaluate the economic profit of each fertilization strategy; and iv) determine the residual effect on a soybean crop after six years following different fertilization strategies. METHODS: The study was conducted across environments in the Salado “A” Basin of the Inland Pampas of Argentina and included seven experiments with a crop rotation of soybean - wheat/second soybean - maize that was managed with different fertilization strategies (with increasing levels of nitrogen –N–, phosphorus –P–, and sulfur –S–), including a non-fertilized control, along six seasons. Additionally, an extra soybean crop was grown in the seventh year to determine the residual influence of previously imposed fertilization treatments. RESULTS AND CONCLUSIONS: The yield response to fertilization was highest under the more intensified treatments and larger for wheat (up to 150%) and maize (up to 100%) than for soybean (up to 40%) and second soybean (up to 30%). Overall crop yield response to increasing N and P inputs was negatively correlated with initial soil extractable P while the response to S was higher in sites with high proportion of sand and low SOM. The economic profit increased as fertilization was intensified although differences were not always significant across treatments within sites. On average, intensification resulted in an additional profit of U$S187 ha−1 compared to the typical fertilization strategy followed by farmers in the area without considering a residual positive yield response (10–13%) observed in a successive soybean crop. SIGNIFICANCE: This study provided elements to improve the understanding of complex interactions determining crop yield response to fertilization strategies to help optimizing long-term management decisions affecting the cropping systems with large impact at regional level.