Steering crop yields, soil nitrogen processes and the microbiome in tropical agriculture system: the role of forage grass cover crops
Authors:   , Momesso Letusa 
Published: August 2023

Cover crops under no-till usually lead to a reduction of negative agricultural impacts
throughout residues accumulated in the soil surface. Introducing different
species of cover crops represents a promising strategy to promote high grain yield, but their effects on plant-soil-microbiome system performance are highly context-dependent and influenced by several factors. The study described in this thesis focused on plant growth performance (maize and upland rice), soil environment and microbial composition. We combined the use of Urochloa as cover crops receiving N input to investigate their effects on plant-soil-microorganism interactions and soil microbial community. In Chapter 2 and 3, we examined the practical effects of N management strategies applied to cover crops on residues production and nutrient accumulation, nutrient leaf concentration, yield components and grain of crops cultivated after Urochloa spp. Results showed that both Urochloa species supply and recycle high amount of residues and N to the tropical no-till system and thus less N can be applied to main crops. In addition, N management strategy is dependent to the subsequent crop because of their N demand to achieve high grain yields.
Maize requires high N amounts than upland rice. Then, N application on pre-seeding could be an alternative management option to supply N to maize because this method resulted in similar nitrogen use efficiency (NUE) as conventional fertilization method; while adjusting early N application to cover crops to increase yields of subsequent rice is an alternative that can promote its production. Both maize and rice performed greater following U. brizantha compared to U. ruziziensis.
As maize has an expressive global cultivation, we continued our study evaluating the effects of N fertilization of cover crops on soil microbiota and the N cycle in tropical grasscrop no-till systems at the end of growing season in Chapter 4. The findings pointed that maize yield increased N fertilizer should be N application time used (currently recommended method following U. brizantha to achieve high crop yield while controlling N loss from tropical soil via nitrification and denitrification.
Similarly, our investigation in Chapter 5 of impact of N inputs to cover crops cultivation on microbiome and N cycle evidenced that, high N uptake by U. brizantha supports the competitive advantage of this plant species over microorganisms for N sources. Clearly, U. brizantha has advantages over U. ruziziensis for use in agriculture systems. Thus, the entire system was investigated in Chapter 6 and confirmed the hypothesis that Urochloa residue maintenance on the soil surface and N addition benefit the growth and grain yield of cash crops as well as the chemical, physical and biological properties of the soil. We considered the Urochloa-maize rotation in no-till as a olistic approach to evaluate soil diversity and crop productivity in agricultural systems.
In conclusion, analyzing the entire agricultural system is a smarter strategy to step
towards improving the soil heath while increasing the crop grain yields. Only Urochloa
brizantha receiving conventional application N method is a planning management practice
as environmental and beneficial approach to farmers.