Nutrient concentration in soil water extracts and soybean nutrition in response to lime and gypsum applications to an acid Oxisol under no-till system

Abstract

No-till system (NTS) occupies 20 million hectares with grain crops in Brazil. However, calcium deficiency and aluminum toxicity can limit crop yields in many soils, and liming, associated to gypsum application, is an option for improving soil management. The objective of this study was to evaluate the effects of lime and gypsum application on the composition of soil water extracts of a clayey Rhodic Hapludox, cultivated with soybean under NTS. The experiment had a randomized complete block design with split-plots. The plots consisted of lime treatments (either a single rate of 4.5 t ha À1 or three annual rates of 1.5 t ha À1 ) surface-applied or incorporated at 0.2 m depth. The subplots received surface applications of gypsum (3, 6 and 9 t ha À1 ). Liming increased total calcium and magnesium concentrations and the magnesium free Form activity (aMg 2+ ) in the water extracts. The effect of liming on Mg was observed at deeper layers of the soil profile. Gypsum increased total concentration and free forms activities at calcium (aCa 2+ ) and sulfate, but decreased to magnesium in the 0.05-0.2 m soil layer. Part of Mg lost from these upper layers probably contributed to increased Mg in the subsoil (0.4-0.8 m). Free forms activities at the aluminum, calcium, magnesium and sulfate were lower than the total concentrations, mainly for aluminum. Ca and Mg concentrations in soybean leaf tissue were positively correlated to the aCa 2+ and aMg 2+ in the soil water extract. Soybean grain yield was negatively correlated to both Mn total concentration and activity (free form) in the soil water extract, but it was positively correlated to sulfate (total concentration and free form activity) in the subsoil layer and to the Ca total concentration in the upper layer (0-0.05 m). It is concluded that lime and gypsum ameliorate soybean grain yield under NTS.

Surface application of gypsum in low acidic Oxisol under no-till cropping system

“…This effect on subsoil was no longer observed 30 months after gypsum application, showing that gypsum rates resulted in the leaching of exchangeable Mg from the soil over time. The leaching of exchangeable Mg in the soil with a gypsum application is facilitated by the formation of the ionic pair MgSO 4 0 and it has been observed in several studies carried out under different conditions of soil and climate (Oliveira and Pavan, 1996;Caires et al, 1999;Toma et al, 1999;Farina et al, 2000b;Zambrosi et al, 2007). Thus, when gypsum is applied at high rates the loss of exchangeable Mg can be minimized by the use of dolomitic lime when correct- Ca/Mg ratio ing soil acidity.…”

Liming and Ionic speciation of an Oxisol under no-till system

“…Liming in acid soils is, most likely, the agricultural practice with the greatest potential for changing the composition of the exchange complex and the liquid phase, due to the quick equilibrium between phases. Thus, liming affects the dynamics of dissolved ions (Amaral et al, 1998;Zambrosi et al, 2007).…”

Lime and calcium-magnesium silicate in the ionic speciation of an Oxisol

“…Where the complexation of Al by F − is intense, it is possible that there has been an application of phosphate fertilizers containing fluoride (Zambrosi et al, 2007). In this study, the average content of F − in the samples was 0.24 mg L −1 , well below that normally present in natural conditions, around 1 mg L −1 (Noemmik, 1953).…”

“…The differences found between Alt and aAl 3+ in aqueous extract suggest that the total concentration of aluminum represents neither its availability nor its potential phytotoxicity (Zambrosi et al, 2007) On average, aAl 3+ corresponded to approximately 3 % of the total aluminum concentration in all five soil layers for all treatments studied. Zambrosi et al (2007) found differences of almost 1 % in their study compared to 40 % in other authors' studies for aAl 3+ in relation to Alt, respectively. However, these other authors did not determine the fluoride content (F − ) for calculating the activity of aluminum in solution.…”

“…OM decomposition under the Season -Fallow system may have occurred gradually, and is possibly explained by several factors, including higher Si in the grasses, which adds rigidity to the plant structure and retards its rate of decomposition (Ramos et al, 2006). In the deeper layers of the soil, where there is no strong presence of organic compounds or correctives, the F − will prevail when combining with Al (Zambrosi et al, 2007), which also depends on the concentration and activity of the fluoride in solution.…”