Atividade microbiota do solo e desenvolvimento da bananeira 'Prata Catarina', submetida à adubação com cloreto de potássio e sulfato de amônio

Abstract

Due to the continuous use of saline fertilizers, such as potassium chloride and ammonium sulfate, the accumulation of salts in the soil has been increasing, especially in regions where evapotranspiration exceeds precipitation. The excess in the availability of ions, triggers a series of physiological disturbances in plants and microorganisms, becoming a potential biocide in the soil. The objective of this work was to evaluate the effect of the application of potassium and nitrogen doses to the microbial activity in Tipic Hapludox and its consequences on the vegetative growth of banana 'Prata'. The first stage of the experiment (year 2016) was conducted under laboratory conditions by aerobic incubation of soil samples. The experimental design was a completely randomized with 11 treatments and 4 replicates, constituting a 5 x 2 factorial (5 doses of K2O x 2 doses of N), + a control plot (without application of K2O and N). The doses of potassium and nitrogen used were: 0, 50, 100, 200 and 400 mg dm-3 of K2O as potassium chloride (KCl) and 200 and 400 mg dm-3 of N as ammonium sulfate ((NH4)2SO4). The soils of the experimental units were incubated in aerobic condition for a period of 90 days in hermetically sealed recipients. After the first stage, the experiment was implanted in a greenhouse (year 2017) with the cultivation of banana 'Prata Catarina' cultivated in Tipic Hapludox. The experimental design was a randomized block with 13 treatments and four replicates, consisting of a factorial 6 x 2 (6 doses of K2O x 2 doses of N), + one control plot (without application of K2O and N). The potassium doses used were: 0, 50, 100, 200, 300 and 400 mg dm-3 of K2O and 200 and 400 mg dm-3 of N, whose sources were potassium chloride (KCl) and ammonium sulfate ((NH4)2SO4), respectively. The seedlings were planted in pots with a capacity of 10L and the following parameters were evaluated: soil electrical conductivity, ammonium and chloride content in the soil, microbial activity, concentration of chlorine in the banana shoot; root and shoot production, as well as biometric parameters during the vegetative growth of the crop. The supply of potassium and nitrogen in doses higher than 200 mg dm-3 of K2O associated with nitrogen fertilization resulted in the accumulation of salts in the soil solution, elevated the electrical conductivity of the solution, caused decrease of the mineralizable carbon emission of the soil as CO2, besides causing significant reduction of N mineralization and N-NO3 availability in the soil. There was a significant reduction of microbial biomass, respiratory rate and metabolic quotient at doses higher than 200 mg dm-3 of K2O and 400 mg dm-3 of N. The increase of chlorine concentrations in soil solution and banana’s shoot with increasing doses of potassium and nitrogen, led to the lower vegetative growth of banana 'Prata Catarina'. It was concluded, therefore, that high doses of potassium chloride and ammonium sulphate resulted in a decrease in the microbial activity and in the vegetative growth of the banana 'Prata' due to the toxic effects caused by the excess of chloride in the soil and plants, being therefore, recommended the careful use of potassium chloride associated with ammonium sulfate in successive fertilizations, especially in semi-perennial crops such as banana.