Phosphorus cycling by Urochloa decumbens intercropped with coffee

Abstract

Summary Phosphorus (P) is a limiting resource for agricultural production in the tropics. Urochloa spp. is commonly used as a cover crop and has mechanisms to mobilize partially the nonavailable P forms from the soil. The use of Urochloa intercropped with Arabica coffee (Coffea arabica L.) is increasing in Brazil, but P cycling has been overlooked in this system. Here, we proposed two experiments to test the hypothesis that Urochloa decumbens could mobilize and absorb P from deep soil layers and increase overall P cycling of the intercrop system. We measured U. decumbens root and shoot dry mass (SDM), root morphology and activity, nutrient uptake, soil nutrient availability, and soil P fractionation in both experiments. To better understand P cycling by Urochloa alone, in the first experiment, U. decumbens was cultivated in rhizotrons where adequate P was supplied in distinct soil layers – 0.0 to 0.3 m, 0.3 to 0.8 m, 0.8 to 1.3 m, and 1.3 to 2 m. Root dry mass (RDM) and morphology were not affected by P availability. Moreover, total biomass production (root plus shoot) and P uptake were higher when P was available in the superficial top soil layer compared to P availability in more than one layer or only in the bottom layer. Nevertheless, U. decumbens was able to reach and acquire P from depth. Correlation analysis showed that P cycling was strongly dependent on SDM, labile, and moderately labile fractions of soil P and was not significantly correlated with RDM. The second experiment aimed at verifying P uptake and mobilization from different soil depths in field conditions. P was supplied in different depths of the soil profile – 0.3 m, 0.6 m, and 0.9 m – in the field with preestablished U. decumbens intercropped with Arabica coffee plants. Shoot P content was higher at the first sample date when P was supplied at 0.3 m, compared to 0.6 m, 0.9 m, and control with no P. Soil P fractionation showed that there was no P mobilization of less labile forms by U. decumbens during the evaluated time. Our results showed that P fertilization in the top layer rather than suppling P trough the soil profile can maximize U. decumbens growth. Also, Urochloa P accumulation was enough to support coffee demand even in high yields and can be an alternative to increase P use efficiency in coffee production systems, being an effective recycler of P.