Agriculture is still by far the back bone of Niger state economy, more than 80% of the population depends either directly or indirectly on it for their livelihood (NSG, 2010). By location, climate and soil, the state is one of the largest and most fertile agriculture lands in the country, with about 80% of the 74,244 sq.kmtotal land area of the state, and has the capacity to produce most of Nigeria’s stable crops. The prevalence of Proteobacteria in many soil ecosystems is associated with various activities involved in biogeochemical cycles, such as carbon, nitrogen, and sulphur (Parihar et al., 2022). It was found to be the dominant phylum in southern and Northern Borgu, with an abundance of 95.98 and 86.41%, respectively. In comparison, Eastern and Western Borgu had a lower abundance of 19.6% and 14.96%, respectively. The high predicted abundance of functions promoting plant growth can be explained by the high relative abundance of Proteobacteria in agricultural soils. Many genera classified as plant growth-promoting rhizobacteria (PGPR) under the phylum Proteobacteria, Firmicutes, and Actinobacteria facilitate nutrient availability and plant fitness (Lotfi, 2022). Hence, Southern Borgu (Kwatanwara, Kale, Kurwasa, Old Kurwasa, New Awaru) and Northern Borgu (Kanu and Puissa) might have higher potential for crop productivity compared to Eastern Borgu (Swashi, Lumma, Dugga, Shagunu) and Western Borgu (Kuble, Guffanti). Firmicutes which were the dominant phylum in Eastern and Western Borgu, this category of microorganisms is recognized for their significant role in enhancing plant growth (biofertilizers), managing plant diseases (biocontrol agents), and eliminating heavy metals from plants (Hashmi et al., 2020). One of the most prevalent phyla of soil bacteria, Actinobacteriota, is well known for its capacity to break down plant remains. Actinobacteria communities physiologically contain the entire set of hydrolytic enzymes required to break down plant residue (Lewin et al., 2016). Additionally, they play a role in nitrogen fixation, the sequestration of carbon in the soil, and the suppression of competitors by producing antibiotics (Swarnalakshmi et al., 2016; Van Bergeijk et al., 2020; Bao et al., 2020).
The variation in soil respiration may result from the nature of the soil and crop planted. The level of soil respiration in these locations indicated improved microbial activities, which may be a result of improved microbial activities in the area, and that can be a result of the rapid transformation of organic waste into nutrients for plants. The results of this work agree with the findings of Zahir et al.(2010), who reported consistently more excellent soil respiration in legume-based rice wheat plots than in fallow-based rice plots. The variations and similarities in the ranges of enzyme activities observed at different locations might be as a result of the crops planted in those locations. The crops planted in all the locations were almost the same, including maize, sorghum, groundnut, and shear butter in some areas. The uniformity of plants in all the locations aided the similarity in their enzyme activities. Our results for phosphatase activities were in line with those who reported improved phosphatase activity under coffee culture. Phosphatase is an enzyme that catalyzes the hydrolysis of both esters and anhydrides of H3P04. It is very important in soil organic P mineralization and plant nutrition (Tabatabai, 1994). High metabolic activities in the soil enhance phosphatase sources and lead to high production of enzymes (Elcio & Julio, 2010). The similarity in Amylase, urease and dehydrogenase activity in all the locations can as well be attributed to the similarity in the soil and crops planted.
A study conducted by Ogbenna et al., (2016) showed that the soils of the study area are still fertile. However, in 2018, Ojo et al. reported the problem of deforestation due to increase in commercial farming, urbanization among other causes, thereby exposing the top soil with subsequent loss of the organic layer. In a similar study, degradation of soils across the locations was observed by Jibrin et al., (2018), thereby emphasizing the decrease that have been happening to the carbon stock and therefore decease in the most of the soil nutrients. Presently, total N of the study area is still low (Fig 6), this is probably due to the loss of N through various ways such as run off, leaching and the loss of N to the atmosphere (Wang et al., 2021). The strongly acidic and near neutra pH of the soils across the local government signifies some level of soil degradation in some parts compared to other local government locations. The areas that was high in C would probably be due to the use of organic materials such as manure and this positively influenced the level of available P, exchangeable K and available Zn in some parts of the state (Gerke, 2022). The heavy metals detected are not toxic to the soil as their concentration was within the WHO permissible limit.