Long-term continuous wheat in semiarid region: Dynamic of soil organic carbon fractions

GALANTINI, J; DUVAL M; IGLESIAS, J; KRÜGER, H

Montevideo

Conferencia; XXIX Conferencia Mundial ISTRO y IV Reunión SUCS; 2012

ISTRO de Uruguay, la Sociedad Uruguaya de Ciencias de Suelos (SUCS), la Facultad de Agronomía de la Universidad de la República Oriental del Uruguay y el Instituto Nacional de Investigación Agropecuaria (INIA)

Continuous wheat, a usual practice in the semiarid region of Argentina, produces variable dry matter production due to low and erratic rainfall together with high evapotranspiration. Because of this, the balance of soil organic carbon (SOC) could be variable along time. The aim of this research was to evaluate the dynamic and long-term changes of SOC fractions in a continuous wheat system. The experiment was initiated in 1983 at the Experimental Station of INTA (EEA Bordenave, Buenos Aires province). Soil samples (0-5, 5-10 and 10-20 cm depth) with continuous wheat, with (f) and without (nf) fertilizer (N+P) application, under conventional- (CT, during 25 years) and no-tillage (NT, during 6 years) were taken nine times during the experiment. A physical fractionation of SOC was performed. The mineral associated (MOC, 0-0.053 mm), fine particulate (POCf, 0.053-0.100 mm) and coarse particulate (POCc, 0.1-2.0 mm) were obtained. The dynamic of SOC showed high variability, depending on water availability during fallow (SOC decomposition) or crop cycle (dry matter production). Mean SOC concentration (0-20 cm depth) were 0.895% (nf) and 1.093% (f). Mean wheat yields were 1.33 (nf) and 2.09 (f) Mg grain ha-1, with a calculated carbon input of 1.64 (nf) and 2.20 (f) Mg C ha-1 yr-1. For an equivalent mass of soil (2400 Mg ha-1), fertilizer application increased SOC by 4.31 Mg ha-1 (mean of three sampling times en CT) and 7.29 Mg ha-1 (in NT). Losses from the initial level were higher in labile fractions, POCf (-53%) and POCc (-75%), than MOC (-15%). No tillage system showed highest SOC with fertilizer application and the lowest without it. No-tillage do not increase SOC content by itself, must be combined with other agricultural practices, like as fertilization and/or crop rotation.