Crotalaria spectabilis Roth as a cover crop in coffee (Coffea arabica) and weed control

Introduction. The establishment of cover crops like C. spectabilis is an agroecological practice with multiple agronomic and environmental benefits. Objectives. To evaluate the effect of 3 C. spectabilis planting methods in coffee on weed control, nitrogen accumulation, and carbon fixation. Also, to determine the period between weed control and C. spectabilis sowing, and the tolerance of C. spectabilis to postemergence herbicides. Materials and methods. The first experiment was carried out in Orosi, Costa Rica, in 2017. C. spectabilis was planted in between coffee planting rows using three methods. The second experiment was carried out in a greenhouse in Alajuela, in 2018. Herbicides glhyphosate, glufosinate ammonium, and diquat were sprayed over pots filled with soil. C. spectabilis was planted 0, 4 and 8 days after spraying, both covered with soil and without cover. For the third experiment C. spectabilis was planted in pots, and when the plants had 2, 3, and 4 leaves, the herbicides fluazifop-p-butyl, clethodim, and bentazon, and the mixes fluazifop-p-butil + bentazon and clethodim + bentazon were sprayed. Results. In Orosi, weed cover was reduced in all treatments by less than 26%, compared to the control. C. spectabilis relative growth rate was low and similar in the 3 planting methods. Nitrogen accumulation and carbon absorption was highest in the covered rows (81.46 kg.ha-1 N and 6.20 t.ha-1 CO2, respectively). In the greenhouse, no negative effect on seed germination or plant growth of C. spectabilis was observed by any treatment. Conclusion. Due to weed competition, it was not possible to establish C. spectabilis as a cover crop in coffee, however herbicides evaluated in a greenhouse could potentially control those weeds.  Keywords: Integrated weed management; green manure; cover crops; pre and post emergence herbicides.