Potential Contribution of Groundnut Residues to Soil N and the Influence of Farmer Management in Western Uganda

Abstract

Through symbiotic biological nitrogen fixation (BNF), grain legumes, such as groundnuts, can enhance soil nitrogen (N) and be an important source of N fertility, as well as a critical component of human nutrition and food security. Because legumes obtain N from soil N stocks as well as BNF, legume residues are key to capturing potential N benefits for soils, which may contribute to increased yields and food production. Here, we conducted a detailed survey at household and field level within a six-village corridor along the western boundary of Kibale National Park (KNP) in western Uganda. We focused on groundnut production and residue management practices and soil organic carbon (SOC) and total N (TN) in fields managed by 100 different households. We also determined SOC and TN in adjacent uncultivated KNP soils. We tested for relationships between socioeconomic factors and farmer groundnut management practices. We calculated a partial N balance and estimated potential N benefits under three scenarios for groundnut BNF. Within the study area, groundnut residue management varied greatly with 51% of surveyed farmers retaining residues on fields through spreading or incorporation, and 49% removing residues, either by transfer to banana groves or burning. Groundnut population density was relatively high with 43% of fields having >30 plants m−2. Despite providing net N inputs of up to 27 kg N ha−1, there was no observed effect of groundnut residue management practices on SOC, TN, or soil C:N ratios. Compared to uncultivated KNP soils, groundnut fields had lower mean levels of SOC and TN and wider C:N ratios. These values are consistent with cultivated soils; however, losses of SOC and TN were lower compared to losses previously reported for conversion from tropical forest to agricultural use. We found that farmer valuation and perception of groundnut residues were influential factors in residue management practices. Overall, we estimated that groundnut residues have the potential to contribute to SOC and TN stocks if retained in the field, but, conversely, removal will result in sizable losses. We find that both environmental and social contexts must be considered when recommending legumes for N provisioning services.

Comparing distinct soil test methods for available nitrogen, phosphorus and potassium for groundnut (Arachis hypogaea L.) and wheat (Triticum aestivum L.) grown in North Western India

“…The combined use of chemical fertilizers and organic manure may have increased organic matter and further mineralization, resulting in an increase in available N, P, and K status. In addition, legumes such as groundnuts, can improve soil nitrogen (N) and be an important contributor of N fertility through symbiotic biological nitrogen fixation (Witcombe and Tiemann, 2022). Significance of combination of different availability indices of N, P and K Various combinations of different availability indices of N, P and K are given in table 2 for groundnut and in table 3 for wheat.…”

Cassava Groundnut Intercropping: A Sustainable Land Management Practice for Increasing Crop Productivity and Organic Carbon Stock on Smallholder Farms

“…This may have contributed to an increase in the total nitrogen in the soil after the decomposition of the groundnut residues thus enhancing the vegetative growth of the cassava plants in the intercropping system to some extent. residues have the potential to contribute to total nitrogen stocks if retained in the field [10]. Even though intercropping had no significant influence on the aboveground biomass of cassava, the aboveground biomass for the sole cassava was higher than the intercropped cassava.…”

“…Average across locations, the SOC stock for the cassava-groundnut intercrop at harvest of the cassava increased by 3.4% when compared to the baseline. Previous research studies have shown that groundnut residues have the potential of increasing SOC if retained in the field, conversely, subsequent removal of the groundnut residues could lead to a sizable loss of SOC from the field [10].…”

“…The conventional tillage practices often result in soil degradation and emissions of carbon dioxide (CO 2 ) into the atmosphere [9]. Groundnut is a cash crop, has the potential to provide household incomes during critical periods (August to September) of food shortages in rural communities, and has the potential to increase SOC in the soil through the decomposition of its crop residues in addition to fixing nitrogen into the soil [10]. As a long-season and wide-spaced crop, the initial growth and development stage of cassava is slow and therefore permits intercropping with short-duration crops in a well-defined spatial crop arrangement and optimum density that will permit efficient use of plant growth factors.…”

“…To this end, intercropping cassava with groundnut on flat land at a modified spatial arrangement could permit the effective use of growth factors for better and higher quality food production, on-farm income and climate change mitigation. In addition, intercropping with groundnut could lead to improved soil fertility, an increase in the amount of organic carbon storage in the soil through the decomposition of crop residue, reduction of nitrous oxide (N 2 O) emissions through nitrogen fixation [10]. This study is therefore useful to generate evidence to support the efficacy of the cassava groundnut intercropping system as a sustainable management practice for increasing crop productivity and building farmers' resilience for climate change adaptation and mitigation.…”