Abstract
In spite of the chemical, physical, and biological benefits that Crotalaria spectabilis can provide to the soil, it is little used as a green manure crop by farmers. Inoculation with strains of legume-nodulating nitrogen-fixing bacteria that are efficient and competitive may be a strategy to enhance accumulation of N in C. spectabilis and stimulate adoption of this green manure crop. The aims of this study were i) to evaluate the symbiotic and agronomic efficiency of new strains of Bradyrhizobium on C. spectabilis in an oxisol (red latosol) compared to that of noninoculated controls (without and with mineral N) and with the approved strain BR2811, seeking to corroborate possible recommendation as inoculants for this species; and ii) to determine, the contribution of these treatments to N accumulation in the plant of C. spectabilis in four periods of cutting for determining possible and ideal periods for its incorporation in the soil. Experiments were carried out in pots and field. Inoculation with the new strains UFLA05-03, UFLA05-09, and UFLA05-14 and with BR2811 on C. spectabilis is effective since it increases the production of N-enriched plant biomass when compared to the control without N mineral. However, UFLA05-03 stands out among these strains because it behaves similarly to the control with mineral N both in relation to shoot N accumulation and dry matter just after 150 days in the field.
Highlights
Green manure is able to increase the productive capacity of soils in a sustainable manner, since it improves the soil physical, chemical, and biological characteristics (Aita et al 2001; Aita and Giacomini 2003; Mercante et al 2014; Moreira and Siqueira 2006)
Mendonça et al (2017) evaluated N dynamics in intercropping between C. spectabilis and coffee and found that, of the total of N accumulated (93.42 kg·ha–1) in the soil, 34.10 kg·ha–1 was derived from biological nitrogen fixation (BNF), and 48.8% of the N originating from BNF was transferred to the coffee plants
The first experiment was conducted to estimate the density of the native populations of nodulating nitrogen-fixing bacteria of C. spectabilis in the soil of an experimental area of the Universidade Federal de Lavras, Lavras, MG, Brazil, from which the soil for the experiment in pots was taken and where the field experiment was conducted
Summary
Green manure is able to increase the productive capacity of soils in a sustainable manner, since it improves the soil physical, chemical, and biological characteristics (Aita et al 2001; Aita and Giacomini 2003; Mercante et al 2014; Moreira and Siqueira 2006). The mean flowering period of this species is 120 days, which can be a limiting factor for its use as a green manure crop on the part of producers who do not have that much time between crop seasons. It can be used intercropped with other species. Resende et al (2003) showed that more than 80% of the N in C. spectabilis can originate from BNF These benefits can be improved if highly efficient strains are used in its cultivation
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