Labranza y Fertilización en el monocultivo de trigo de la región semiárida Bonaerense

Continuous wheat in semiarid regions: Long-term effects on stock and quality of soil organic carbon

Juan A. Galantini, Matias E. Duval, Julio O. Iglesias and Hugo Kruger

Continuous wheat (Triticum aestivum L.) cropping in semiarid regions results in variable dry matter production. As a consequence, the balance of soil organic carbon (SOC) may vary over time. The aim of this research was to assess the dynamics and long-term changes of physically and chemically extracted SOC fractions. Soil samples (0-5, 5-10 and 10-20 cm depths) from continuous wheat, with (f) and without (nf) fertilizer (N+P) under conventional- (CT, for 25 y) and no-tillage (NT, for 6 y) were taken during the experiment. Mineral-associated (MOC, 0-0.053 mm), fine particulate (POC_f, 0.053-0.100 mm) and coarse particulate (POC_c, 0.1-2.0 mm) SOC and humic substances were obtained. SOC variability was depending on water availability during fallow periods (SOC decomposition) or crop cycles (dry matter production). The mean wheat yields were 1.33 (nf) and 2.09 (f) Mg grain ha^-1, with an estimated carbon input of 1.64 (nf) and 2.20 (f) Mg C ha^-1 yr^-1. Losses from the initial level were higher in labile fractions, POC_c (-75%) and POC_f (-53%), than in MOC (-15%). Humic acids present slight differences in their structure and quantity as a result of long-term cropping. Conversion from CT to NT resulted in contrasting results. For an equivalent soil mass, fertilizer application increased SOC by 4.31 Mg ha^-1 (under CT) and 7.29 Mg ha^-1 (under NT). The SOC turned out to be higher under NT with fertilizer use and lower without application. No-tillage does not increase SOC content by itself; it must be combined with other agricultural practices, such as fertilization and/or crop rotation.

Keywords: Fertilization, Tillage system, Physical organic carbon fractions, Humic substances

Galantini Juan A., Matias E. Duval, Julio O. Iglesias and Hugo Kruger. Continuous wheat in semiarid regions: Long-term effects on stock and quality of soil organic carbon. Soil Science (In press)