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.
Some cyanobacteria strains have biofertilization and ⁄ or bioconditioning effects in soils as a result of their ability to fix dinitrogen or produce exocellular polysaccharides. The objective of the present study was to screen indigenous cyanobacteria strains with the potential to improve the N fertility and structural stability of degraded soils, and evaluate their ameliorative effectiveness in semiarid soils of the Eastern Cape, South Africa. Soils from Guquka, Hertzog and Qunu villages, and Fort Cox College were used in the screening study. The results showed that only three cyanobacteria strains (3g, 3v and 7e) out of 97 isolated strains were heterocystous, with appreciable nitrogenase activity and the ability to produce exocellular polysaccharides. Nostoc strains 3g and 3v had a greater ability to produce exocellular polysaccharides, but low potential to fix dinitrogen (4.7 and 1.3 nmol C 2 H 4 lg )1 chl h )1 , respectively). Strain 7e had the greatest ability to fix dinitrogen (16.1 nmol C 2 H 4 lg )1 chl h )1 ), but produced fewer exocellular polysaccharides. The ability of strains 3g and 7e to influence maize dry matter (DM) and soil C and N contents was tested in a nitrogen-poor soil with Nostoc strain 9v as a reference strain. Potted soils with and without growing maize plants were inoculated with the different cyanobacteria strains in a glasshouse at a rate of 6 g m )2 soon after maize emergence. Harvesting and soil sampling were done 6 weeks after inoculation. Inoculation with strains 3g and 7e increased maize DM and N uptake significantly, on par with the reference strain. These increases were consistent with increases in nitrate-N observed at harvest time in inoculated cropped and non-cropped soils. Strain 7e resulted in greater increases in soil nitrate-N, tissue N and uptake than strain 3g, perhaps because of its greater ability to fix dinitrogen. Cropping with maize reduced soil total C and N, possibly owing to its negative effects on cyanobacteria establishment. These results suggest that indigenous cyanobacteria strains screened for greater N 2 -fixing ability have the potential to improve the productivity of N-poor soils in semiarid regions in South Africa.
Two South African cyanobacteria strains (coded 3g and 7e) of the genus Nostoc were evaluated for improvement of the aggregate stability of a silty loam soil with low organic C content and compared with Nostoc strain 9v isolated from a Tanzanian soil. The soil was either cropped with maize or noncropped and inoculated with the three strains in a glasshouse. After 42 days, the aggregate stability based on mean weight diameter (MWD) and fragment size distribution were determined by fast wetting, wet stirring and slow wetting methods. Inoculation of the soil with strains 3g and 7e improved the soil's MWD and increased its proportion of large aggregates, particularly in the cropped soil. The opposite was the case for aggregates in soils inoculated with the reference strain 9v. Strain 3g resulted in greater improvement of MWD estimated by fast wetting, while strains 7e and 9v improved aggregate stability estimated by wet stirring. Improvement of aggregate stability was more related to exocellular polysaccharide (EPS) content than organic C. The results suggest that indigenous strains with high potential for EPS production could improve the soil structural stability of degraded soils in South Africa.
Medicago sativa (lucerne) is a widely used perennial fodder crop and ranked amongst the highly nutritive fodders globally. This study assessed the nutritive value (i.e. CP % and TDN %) of four lucerne cultivars under two soil types at Bathurst Research Station. A random grid (quadrant) sampling method was used for sampling and samples were submitted to the laboratory for analysis to determine forage quality. Data collection was carried out by separating harvested biomass for each cultivar using clean packs, weighed and dried at 70˚C for 48 hours then crude protein (CP %) and Total Digestible Nutrients (TDN %) were determined. The results of the study showed that soil type (site) had a significant (P < 0.05) effect on the overall quality of dry matter produced. In soil 1 (S1) the overall CP % content was 11.48% while it was 19.03% in soil 2 (S2). Cultivar 3 (KKS 9911) was the least nutritive cultivar in site 1, while the same cultivar was the most nutritive cultivar in site 2 pertaining CP content. Soil type also significantly affected (P < 0.05) the overall total digestible nutrient (TDN %) content of different lucerne cultivars. In S1, C4 (WL 525) had the highest (P < 0.05) TDN content in comparison to the rest of the cultivars while in the same soil type C1 (SA Std.) had the least TDN content. The four tested lucerne cultivars generally produced highly nutritive lucerne in S2 while they produced less nutritive lucerne in relation to both CP and TDN content in S1.
Medicago sativa (lucerne) is a perennial and drought tolerant fodder crop which is widely used as feed for livestock in South Africa. This study evaluated four lucerne cultivars under two water regimes and also determined the effect of soil type on lucerne biomass production. To determine dry matter production per cultivar per treatment, a random grid (quadrant) sampling method was used and all biomass within that radius was cut to 5 cm above the ground level in each plot. All biomass sampling was done just before regrowth commences. Biomass data collection on four lucerne cultivars belonging to different dormancy groupings (WL 711, WL 525 HQ, KKS 9911 and SA Standard) were collected seasonally under different soil types on both irrigated and non-irrigated plots and analysed. Soil type (site) had a significant (P < 0.05) effect on the overall quantity of dry matter produced as more dry matter was produced in site 2 (S2) in comparison to site 1 (S2). Different levels of water application (moisture supplementation) also affected the quantity of dry matter produced in each soil type. The once-a-month irrigation treatment (Ir1) led to the production of superior dry matter yield on SI even though the effect was
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