Nostoc cyanobacterial inoculation in South African agricultural soils enhances soil structure, fertility, and maize growth

Abstract

Many soils in South Africa have low nutrient supply, poor structural stability and are prone to soil erosion due to susceptibility to surface sealing and crusting. Two crusting soils from the Eastern Cape Province, South Africa were used to evaluate the effects of inoculation with a strain of Nostoc on soil structure, fertility and maize growth. The Nostoc suspension was uniformly applied over potted soils at a rate of 6g (dry weight) per square meter soon after maize germination.Nostoc inoculation increased soil N by 17% and 40% in Hertzog and Guquka soils, respectively. Soil C was also increased significantly and this increase was strongly associated with that of soil N (R 2 = 0.838). The highest contents of soil C, soil N and mineral N, however, were found in non-cropped Nostoc inoculated soils. Nostoc inoculation increased maize dry matter yields by 49% and 40% in Hertzog and Guquka soils, respectively. Corresponding increases in maize tissue N were 23% and 14%, respectively. Scanning electron microscopy (SEM) revealed that soil particles and fragments of non-cropped inoculated soils had coatings of extracellular polymeric substances (EPS) with other particles enmeshed in networks of filaments, whilst by contrast little or no EPS and/or filaments were observed on cropped and/or non-inoculated soils. This was consistent with chemical analysis which showed that Nostoc caused significant increases in the EPS and soil C contents of non-cropped soils. The proportion of very stable aggregates was increased by inoculation with Nostoc possibly due to the greater quantities of soil C and EPS observed in inoculated soils. Inoculated soils cropped with maize had a lower proportion of stable aggregates presumably due to their low soil C and EPS contents compared to non-cropped soils. The results suggested that Nostoc could improve the fertility and structural stability of the studied degraded soils.

Selection of Hyper Exopolysaccharide Producing and Cyst Forming Azotobacter Isolates for Better Survival under Stress Conditions

“…Further, the development of good aggregate and structure by the binding substances produced by the added bacterium might have reduced the volume of soil solids and consequently the bulk density. These results confirm the findings of Maqubela et al, (2009), who observed a decrease in bulk density of soil on the addition of organic matter. This reduction might occur directly by dilution of the soil matrix with a less dense material or indirectly by the improvement of aggregate stability.…”

Exopolysaccharides produced by the symbiotic nitrogen-fixing bacteria of leguminosae

“…The EPS of Nostoc ssp. contributes not only to the soil biochemical properties but also to soil fertility, once the EPS produced by this cyanobacterium increases the soil C pool as carbohydrates (Maqubela et al, 2009). Also, the water retained in the EPS matrix reduces evaporation losses and potentially increases the waterholding capacity of the soil (Mager, 2010).…”

Effect of Different Anabaena variabilis (Kütz) Treatments on Some Growth Parameters and Physiological Aspects of Hordeum vulgare L. and Trigonella foenum-graecum L.

“…Cyanobacteria can enrich the soil with micro and macronutrients, plant growth regulators and different bioactive secondary metabolite compounds that inhibit the growth of soil pathogenic bacteria and fungi (Karthikeyan et al, 2007). In addition they secrete mucilage and polysaccharide materials that improve soil structure, porosity, aggregation stability and fertility, thus enabling recovery of poor soils and increase plant growth (Osman et al, 2005 andMaqubela et al, 2008) .…”