Cover crops in the Southeastern region of Buenos Aires, Argentina: effects on organic matter physical fractions and nutrient availability

Abstract

In the Southeastern region of Buenos Aires province, soybean monoculture has led to a decline in soil organic matter (SOM) levels in soil, mostly the labile fractions. The reduction of SOM has a negative impact on the soil environment. Cover crops (CC) constitute an alternative to maintain or improve SOM levels. The aim of this study was to determine the effect of oat as CC on (a) the SOM dynamics and (b) the availability of macro- and micronutrients in a representative soil of the Southeastern region of Buenos Aires province. Total organic carbon (TOC) and nitrogen (TON), as well as their labile and mineral-associated fractions, and macro- and micronutrient availability were determined. The treatments were soybean monoculture with and without oat as cover crop. The increases in SOC and TON were 22.7% and 11%, respectively, when CC was included to the soybean monoculture. These increases were observed mostly in the labile fractions, with increases of 61.3 and 38.7% for the particulate coarse organic carbon (PCOf) and particulate fine organic carbon (PCOf), respectively, and 79.2% for the particulate coarse organic nitrogen (NOPg). Regarding the nutrients, an increase of 47.6% was observed in manganese (Mn) in the first 5 cm of soil depth, and a decrease in phosphorous (P) availability in the same soil layer due to its consumption and retention by CC. It can be conclude that CC presented a surface soil effect on the dynamic of SOM, increasing C, N, and available Mn contents, but decreasing soil P availability.