Fertilizer interactions with micronutrients in tropical volcanic soils

Abstract

Background information for the development of this research:Around the year 2010, we studied nutrient management for papaya (Carica papaya L.) production systems in Costa Rica. The main reason to study these production systems was that papaya is principally grown by small farmers in Costa Rica, who generally operated under low input conditions and limited technical assistance. In addition, there was a general lack of essential information about the correct management of this crop. Firstly, we characterized the nutrient uptake for a high-yielding papaya hybrid (Figure 1.1) . As a result, we found that papaya absorbed amounts of nutrients that exceed the quantities typically applied by farmers, and the fertilizer amounts previously applied were not compensating for total plant nutrient uptake. The application of lower quantities of fertilizer compared to the plant nutrient uptake have several consequences for growers and for the soil system, for instance low productivity per unit area, and depletion of nutrients. Additionally, the nutrient management in papaya production systems is difficult because of the variation of the nutrient requirements over time. Papaya nutrient uptake is concentrated in short periods of time (Figure 1.1), which complicates the correct supply of highly demanded nutrients according to their uptake by the plant. Excessive input of a specific fertilizer in the soil could produce side effects like competition with other ions and increased leaching rates.According to previous observations of the high nutrient demand for the papaya production systems, the growers have increased the addition of fertilizer rates (basically N-P-K) considerably, but this decision lacked agronomical and environmental evidence that justify this practice. Consequently, we have developed field experiments to evaluate the agronomical effects (possible decreasing of yield gaps) of the application of increased N and K fertilizer rates in papaya. The results of this experiment for a dystric volcanic soil are shown in Figure 1.2. From these experiments we observed a noticeable increase in the number of fruits per plant when adding high rates of N and K. These results thus support the use of high fertilizer rates in papaya production systems.The decision to apply increased fertilizer rates for papaya production systems, however, did not consider the environmental consequences of the movement of concentrated solutions through these soils mainly because the possible consequences were not completely understood. Concerned about potential environmental implications due to increased nutrient management in papaya production systems, we realized that the addition of high fertilizer rates is a common practice in other large-scale agricultural production systems and is common for intensive production systems developed in permeable volcanic soils.For instance, more than 43.000 hectares are currently cultivated with bananas in Costa Rica (CORBANA, 2022), receiving high rates of N-P-K fertilizers to account for the high yields required by...