Uncovering the Benefits of Cover Crops in Temperate Cropping Systems: First Results from a Long-Term Experiment in the Rolling Pampa, Argentina.

Cover crop benefits have been largely studied in temperate cropping systems worldwide. Sowing cover crops during the cool-season, particularly before summer crops, presents several advantages, such as increasing annual carbon inputs, weed suppression, and nitrogen leaching reduction. Interestingly, cover crops are rarely grown in grain cropping systems in the Argentine Pampas, notwithstanding the investigations carried out in a wide range of conditions. Moreover, information about when including cover crops in rotational schemes is still scarce. Hence, aiming at disentangling the effects of cover crops in crop rotations, a long-term experiment was started in Pergamino (S33.9°, W60.6°), Argentina, in 2014. Before soybean, triticale-hairy vetch cover crops were sown, which had maize or soybean as preceding crops. Treatments without cover crops were also included. Only soybean crops in the second cropping season were compared. The inclusion of cover crops and the preceding crop type significantly affected soybean yields (p<0.001), without significant interaction (p>0.1). Higher yields were obtained without cover crops (3.23 t ha^-1 vs 2.9 t ha^-1). Soybean yields with maize as preceding crop (3.44 t ha^-1) were higher than with soybean (2.74 t ha^-1). Low yields of summer crops grown after cover crops have been reported under particular agronomical and environmental conditions. This could be attributed to water availability to the following summer crop and/or nitrogen immobilization during cover crop decomposition. Although cover crops do increase annual carbon input in continuous cropping systems, avoiding yield losses requires to disentangle the intermingle effects between agronomical and environmental factors. Such yield losses could be mitigated by managing the sowing pattern and density of cover crop mixtures, fertility, timing between herbicide application to terminate cover crops and crop sowing date. Widespread adoption of cover crop by farmers can be promoted by revealing their long-term benefits through uncovering the factors undermining yields.