Limitations and strategies to enhance biological nitrogen fixation in sub-humid tropics of Western Ethiopia

Abstract

Currently, inorganic nitrogen fertilizer becomes a serious threat to the environment and human health. Thus, finding alternate source of nitrogen is a viable option in assuring sustainable agricultural system. Biological nitrogen fixation is a critical and key process in sustainable agricultural systems in tropical soils, which are frequently deficient in N and susceptible to leaching of plant nutrients. This process transforms atmospheric nitrogen to ammonia, nitrate and nitrogen dioxide. Several key abiotic and biotic factors limit legume productivity and biological nitrogen fixation in World agriculture, especially in sub-Saharan Africa. Within the soil, rhizobia frequently encounter various stresses that affect their growth, initial steps of symbiosis and capability of nitrogen fixation. Biotic and abiotic stresses impose a major threat to agriculture and symbiotic nitrogen fixation is dependent on host cultivar and rhizobia, but as well may be limited by pedoclimatic factors. The most common factors affecting biological nitrogen fixation and symbiosis activity in western parts of Ethiopia are soil acidity, quality of inoculants and low soil fertility. In most cases, the microsymbiont is the more affected partner, with plants growing on mineral N usually less sensitive to these stresses. Thus, it can be concluded that, particularly in a western part of Ethiopia, many studies should be focused on acidity related constraints on biological nitrogen fixation, screening of acid tolerant inoculants and low soil fertility improvements to enhance biological nitrogen fixation in smallholder farming system.

Soybean-Nodulating Rhizobia: Ecology, Characterization, Diversity, and Growth Promoting Functions

“…Moisture availability of the soil is determined by soil moistureretaining capacity (Hungria and Vargas, 2000). Moisture stress in the soil results in the reduction of nodule weight and nitrogenase activity and hence affects the N 2 fixation process (Siczek and Lipiec, 2011;Dabessa et al, 2018;Santachiara et al, 2019). Although some rhizobial populations occur in desert soils and are effective in nodulation, viable strains cannot survive or function under high moisture stress (Lucrecia et al, 2003;Bashan et al, 2014;Dabessa et al, 2018).…”

“…Moisture stress in the soil results in the reduction of nodule weight and nitrogenase activity and hence affects the N 2 fixation process (Siczek and Lipiec, 2011;Dabessa et al, 2018;Santachiara et al, 2019). Although some rhizobial populations occur in desert soils and are effective in nodulation, viable strains cannot survive or function under high moisture stress (Lucrecia et al, 2003;Bashan et al, 2014;Dabessa et al, 2018). Drought is among the major environmental stresses which affect the survival of N 2 -fixing bacteria and the nodule initiation stage because plants need more adequate moisture during this stage than other stages (Monica et al, 2013).…”

“…P is a very important nutrient in the symbiotic association process as it is involved in plants' energy (ATP) acquisition, storage, and utilization (Mmbaga et al, 2014). Iron (Fe) and aluminum (Al) abundance in acidic soil, as well as calcium (Ca) and magnesium (Mg) abundance in alkaline soil, fix soil P in the form of oxides and hydroxides, rendering P unavailable for plant uptake (Dabessa et al, 2018).…”

Response of Field Pea (Pisum sativum L.) to Rhizobium Inoculation and NPS Fertilizer Applications in Western Ethiopia

“…Therefore, using effective rhizobia strains that tolerate soil acidity and selecting field pea genotypes or varieties are options for increasing yield and BNF in field peas. Inoculating food legumes with Rhizobium strains is not a common practice in Western Ethiopia, but it could provide an option for increasing seed yield in low nitrogen acidic soils 12 .…”

Response of Fertilization of Nitrogen on Agronomical Attributes of Soybean

“…There are several additional benefits associated with the additional application of nitrogen in the soybean including enhanced seed yield, nodules formation, improving availability of nitrogen to the crop [12]. Again, there are several constraints to biological nitrogen fixation resulting poor availability of nitrogen which ultimately will cause reduced grain formation, test weight and thus will affects crop productivity [13]. Only 25% to 60% of nitrogen in soybean dry matter comes from symbiotic nitrogen fixation, remaining requirement is fulfilled from soil nitrogen [14].…”