Soil and crop responses to lime and fertilizers in a fire-free land use system for smallholdings in the northern Brazilian Amazon

The purpose of this study was to investigate the effects of lime and fertilizers in a fire-free system for land clearing. Four replications of the split-plot experimental design were used, and two treatments were chosen for the main plot: lime (1tha⁻¹) or no lime. Fertilizer levels zero (1), low (2), and high (3) were evaluated in the subplots over a period of three years. In 2006 and 2008 treatments were evaluated while using corn (Zea mays L.) intercropped with rice (Oriza sativa); the evaluations of 2007 were carried out while cropping cowpea (Vigna unguiculata L.). In plots without lime on which fertilizer level 3 was applied, the soil pH decreased by 0.4 and 0.8 in 2006 and 2007, respectively. The effects of the fertilizer levels reducing the soil pH were observed in 2007 (plots without lime) and in 2008 (plots with or without lime). Organic soil matter increased with liming and fertilizer level 3. Soil calcium and magnesium increased with liming and fertilization, while available phosphorus increased only with fertilizer level 3. Lime and fertilization increased the nutrient content in plant tissue, however it did not lead to an equilibrium of nutritional status. The increase of corn and rice yields was related to the fertilizer levels rather than to liming, but the cowpea yield was responsive to both liming and fertilizers. The most positive financial balance was observed to with fertilizer level 2 (without liming) after three years; however, the difference between level 2, with or without liming, was small. Fertilization without liming is an option for the first year of a fire-free system for land clearing, assuming corn is intercropped with rice. Lime application from the second year on is important to allow better yields of subsequent crops and to avoid soil acidification by inorganic fertilizers.