Soil management and efficiency of rhizobia strains of cowpea Vigna unguiculata (L.) Walp. in the tropics

José Geraldo Donizetti dos Santos1, Alana das Chagas Ferreira Aguiar2, Edilson Máximo Silva Junior3, Danúbia Lemes Dadalto3, Merijane Rodrigues Sousa3, Gustavo Ribeiro Xavier4, and Emanoel Gomes de Moura3*

In the humid tropics, the largest obstacle to the implementation of sustainable farming systems is the reduced efficiency of nutrient use by crops. This study assesses the effectiveness of five selected rhizobia strains in symbiosis with cowpea (Vigna unguiculata (L.) Walp.), with the objective of replacing N fertilization in the predominant agricultural system used by smallholder farmers. The study was carried out in three adjacent areas with distinct agricultural uses: conventional tillage, itinerant agriculture, and a no-till system. The experimental design was in randomized complete blocks with four replicates and seven treatments: five rhizobia strains (BR3262, BR3267, BR3299, INPA3-11B, and UFLA 3-84) and two controls without inoculation (one without mineral N and another fertilized with 74 kg N ha-1). We measured the dry mass of 100 grains, nodules and shoots, as well as cowpea yields and calculated relative and absolute efficiency indices for dry biomass production of cowpea shoots. Agricultural uses affected the number and dry mass of the nodules and, consequently, the mass of the dry plant matter and bean yield. In terms of yield, there was a major difference between the conventional and the itinerant systems. Yield was around four times as high in the itinerant system (1009.9 kg ha-1 compared to 243.7 kg ha-1). Under conditions of cohesion-prone soils, the system of conventional tillage reduces the possibility of cultivation of a second harvest in the year even with inoculation or N fertilization.

Keywords: agroecosystem, nitrogen-fixing nodule bacteria, legumes, Vigna unguiculata.
1Universidade Federal do Tocantins, Campus Universitário de Araguaína-EMVZ, BR 153, km 112, CP 132, 77804-970, Araguaína, Tocantins, Brasil.
2Universidade Federal do Maranhão, Centro de Ciências Agrárias e Ambientais, BR 222, km 04, 65500-000, Chapadinha, Maranhão, Brasil.
3Universidade Estadual do Maranhão, Programa de Pós-Graduação em Agroecologia, CP 3004, 65000-000, São Luís, Maranhão, Brasil. *Corresponding author (egmoura@elo.com.br).
4Empresa Brasileira de Pesquisa Agropecuária. Embrapa Agrobiologia, BR 465, km 47, 23890-000, Seropédica, RJ, Brasil.