Liberação de fósforo de fertilizantes mineral e organomineral e sua influência na fase inicial da cultura do milho

Abstract

Among the nutrients, phosphorus is one of the elements of great importance for the development and production of maize, since its availability under natural conditions is very low due to the high P fixing capacity in soils. In the soil, phosphorus is found in inorganic and organic form and the supply of P can be realized by several types of fertilizers, among them the mineral and organomineral. The objective of this work was to quantify the inorganic and organic phosphorus fractions in soils of different texture, as a function of the use of mineral and organomineral P sources cultivated with maize. The experiment was conducted at Embrapa Agropecuária Oeste, in Dourados-MS, and two soils were used: a sandy textured Latosol (LVd) with a average texture and a clayey Latosol (LVdf). The experimental design was completely randomized (DIC), in a factorial scheme. For the P fractions in the soil, the design was DIC, in a 2x4x5 factorial scheme for each soil, where the treatments consisted of two sources of P (mineral and organomineral), four P (0, 40, 80 and 120 mg kg-1 of P) and five epochs (0, 7, 14, 28 and 49 days after emergence) with four replicates. For the variables stem diameter and plant heights, the treatments were arranged in DIC, in factorial scheme 2x4x10, for each soil and the treatments were composed of two sources of P (mineral and organomineral), four doses of P (0, 40, 80 and 120 mg kg-1 of P) and 10 days of evaluation (4, 9, 14, 18, 23, 28, 32, 37, 42 and 49 days after emergence), with four replicates. For the variables leaf area (FA), leaf dry mass (MSF), stem dry mass (MSC), shoot dry mass (MSPA) and P accumulated in shoot (P accumulated), the design was set out in DIC in a 2x4 factorial scheme, with two P sources (mineral and organomineral) and four P doses (0, 40, 80 and 120 mg kg-1 P), with four replicates. The variables analyzed were corn height, stalk diameter, leaf dry matter (MSF), stem dry mass (MSC), dry shoot mass (MSPA), accumulated P in MSPA and inorganic and organic fractions of P. The phosphorus that was added to the soil samples in both sources of P increased mainly the non-labile fraction and, to a lesser extent, the fractions that make up the labile P. In general, in both studied soils, the labile P was higher when using the mineral source. For the moderately labile P, in the LVd soil, the contents of PiNaOH 0.1 and PiNaOH 0.5 were higher when using the mineral source and the PoNaOH 0.5 with the use of the organomineral source, in the LVdf the highest contents of PiNaOH 0.1 and PoNaOH 0.1 were found when using the mineral source and PoNaOH 0.5 with the use of the organomineral source. In the non-labile fractions, the organomineral source provided higher levels of PiHCl in both soils and residual P was the predominant fraction, regardless of the P source used. Although the two sources contained the same amount of phosphorus, the mineral source provided higher P content, reflecting higher values of stem diameter, plant height, FA, MSF, MSC, MSPA and P accumulated in maize plants.