Introduction to Soil Science: AGS 211

Introduction to Soil Science: AGS 211, degree examination January 2011

Effects of goat manure and inorganic phosphate addition on soil inorganic and microbial biomass phosphorus fractions under laboratory incubation conditions

Changes in inorganic phosphorus (P) and soil microbial biomass P following the addition of goat manure and different amounts of inorganic P to an Umbric Ferralsol were assessed over 12 weeks under laboratory incubation conditions using a sequential fractionation procedure. Triple superphosphate was added at rates equivalent to 0, 45, 90, 135 and 180 mg P kg-1, with or without goat manure at a rate of 10 g kg-1soil on a dry-weight basis and incubated moist. Resin P, 0.5 mol L-1 NaHCO(3) extractable inorganic P (NaHCO(3)-P(i)), 0.1 mol L-1 NaOH extractable inorganic P (NaOH P(i)) and soil microbial biomass P concentrations were determined on days 7, 14, 28, 56 and 84. The magnitudes of the inorganic P fractions extracted were: NaOH P(i) > Resin P > NaHCO(3) P(i). Thus, NaOH P(i) was the major sink for the applied P. The dynamics of the three labile P fractions (resin P, NaHCO(3) P(i) and microbial biomass P) varied considerably during the incubation period. The resin P fraction consistently declined with time in all treatments, whereas the NaHCO(3) P(i) fraction changed little with time in the control and goat manure amended soil, but increased rapidly with time when inorganic P was applied alone or in combination with goat manure. Microbial biomass P increased with time in all treatments, peaking on day 28 and declining thereafter. The co-application of inorganic P with goat manure produced up to twofold more microbial biomass P than either inorganic P or goat manure applied alone. Therefore, the combined application of manure with low rates of P fertilizers may be a cost effective strategy for increasing the efficiency of fertilizer P use through enhanced biological cycling of P in small-holder farms in South Africa

Introduction to Soil Science: AGS 211

Introduction to Soil Science: AGS 211, degree/diploma examination June 2011

Introduction to Crop Science: AGS 211

Introduction to Crop Science: AGS 211, supplementary examination August 201

Goat manure application improves phosphate fertilizer effectiveness through enhanced biological cycling of phosophorus

High phosphate fixation necessitates the application of high rates of phosphorus (P) fertilizers to achieve reasonable crop yields in most tropical soils. The present study investigated the efficacy of goat manure in improving the effectiveness of fertilizer P for increasing maize yields. Treatments consisted of combinations of four rates of goat manure (0, 2.5, 5 and 10 g kg-1 equivalent to 0, 5, 10 and 20 t goat manure ha-1, respectively) and four rates of inorganic P (0, 45, 90 and 180 mg P kg-1 equivalent to 0, 90, 180 and 360 kg P ha-1, respectively) applied to 7 kg soil in pots. Maize (Zea maize L.) was sown immediately after application. Maize dry matter yields (maize yield) and the concentrations of resin P, soil microbial biomass P (biomass P), 0.5 mol L-1 NaHCO(3) extractable inorganic P (NaHCO(3)-P(i)) and 0.1 mol L-1 NaOH extractable inorganic P (NaOH-P(i)) were determined 6 and 12 weeks after planting. After 12 weeks, maize yield increased with the addition of fertilizer P or goat manure separately and was further increased when they were applied together. These synergistic effects on maize yield were ascribed to enhanced P cycling because goat manure increased the concentration of biomass P, which in turn accounted for most of the observed variations (63%) in maize yield. The combination of biomass P and resin P, however, explained a greater proportion of the variations in maize yield (73%), suggesting that the usefulness of biomass P as an index of P availability would be enhanced if used in conjunction with resin P. These results indicated that goat manure application could be used to increase soil microbial biomass P, which in turn could improve the effectiveness of fertilizer P in the Eastern Cape, South Africa

Effects of cyanobacteria strains selected for their bioconditioning and biofertilization potential on maize dry matter and soil nitrogen status in a South African soil

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 C2H4 μg-1 chl h-1, respectively). Strain 7e had the greatest ability to fix dinitrogen (16.1 nmol C2H4 μg-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 N2-fixing ability have the potential to improve the productivity of N-poor soils in semiarid regions in South Africa. © 2010 Japanese Society of Soil Science and Plant Nutrition.This work was part of a European Union INCO-DEV funded research programme in Southern Africa (CYANOSOILS), Project ICA4-CT-2001-10058. The National Research Foundation of South Africa granted a fellowship to the first author to undertake the study at the University of Fort Hare. We thank Antonia Herrero and José Enrique Frías of Instituto de Bioquímica Vegetal y Fotosíntesis, Consejo Superior de Investigaciones Científicas, Sevilla, Spain, for their assistance with the isolation and characterization of the cyanobacteria strains

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

13 pages, figures, and tables statistics.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 (R2 = 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.This work was part of an EU, INCODEV funded research programme in Southern Africa (Cyanosoils), Project ICA4-CT-2001-10058.Peer reviewe