BIOLOGICAL ACTIVITY IN SURFACE HORIZONS OF SOILS IMPLANTED WITH PEAR CV. WILLIAMS IN UPPER RÍO NEGRO VALLEY, ARGENTINA

Abstract

The objective of the study was to evaluate the seasonal patterns of physical-chemical properties, biological and enzymatic activities in soil surface horizons implanted with pear (Pyrus communis) trees cv. Williams. The study was conducted during three growing seasons, in three commercial orchards with ten experimental sites in each location. Soil samples were collected in spring and autumn. Soil texture, pH, electrical conductivity (EC), exchanging sodium percentage (PSI) total organic carbon, potassium exchange, biomass carbon (C-BM), respiration (RE), dehydrogenase (DH-ase), mineralization index (MI) and ratio of fungivores to bacterivores nematodes (F/B) were determined. Multiple factorial analyses were used to group the sites according to spring or autumn measurements. CE and PSI decreased 25% in autumn in saline soils. The levels of C-BM and RE varied between 113 and 179 mg C 100 g-1 ss and between 5.5 and 8.7 mg CO2 g-1 ss in spring, while in autumn they varied between 57 and 110 mg C 100 g-1 ss and 2.8 and 5.3 mg CO2 g-1 ss, respectively. Dh-ase
levels were lower in shallow soils and higher in saline soils (1.7 µg TPF g-1 h-1). MI showed loss of COT in spring due to high mineralization in all soil groups. F/B was lower in saline soils (0.24) than in shallow soils (0.80) and deep and non-saline soils (0.66), indicating that bacteria mediated decomposition. In the last two groups of soils, fungivores had more contribution to the decomposition processes. Value of F/B did not change between seasons in each soil group.