Total organic carbon, aluminium and iron in bulk samples and aggregate size fractions of a sandy clay loam humic soil under sugarcane relative to native forest in northern KwaZulu-Natal, South Africa.

The distribution of total aluminium (Al) and iron (Fe) and organic carbon (TOC) in aggregate fractions gives an insight into the dynamics of these elements in soil. This study determined the effects of over 30 years of sugarcane cultivation, compared to adjacent native forest, on Al, Fe and TOC in bulk soil and aggregate fractions within the 100 cm depth of a sandy clay loam humic soil. Samples were separated into large macro-aggregates: LM (>2000 µm), small macro-aggregates: SM (250-2000 µm), micro-aggregates: M (250-63 µm) and silt + clay: SC (<63 µm) fractions. The TOC was analyzed by dry combustion and total Al and Fe by X-ray fluorescence spectrometry. Sugarcane cultivation (i) reduced macro-aggregates and TOC and (ii) increased the SC fraction and total Al and Fe. The mean weight diameter declined from 1.32 mm (0-30 cm) to 1.06 mm (30-100 cm) under forest. Average (0-100 cm) Al and Fe contents (g kg-1) increased in LM (6-16 for Al; 6 to 9 for Fe), SM (7-11 for Al), M (5-14 for Al; 6 to 9 for Fe) and SC (7-16 for Al; 9 to 10 for Fe) under sugarcane relative to forest. The TOC (g kg-1) declined in the LM (13-7) and SM (7-6) but increased in the M (5-9) and SC (10-13) due to cultivation. These findings suggested that sugarcane cultivation decreases aggregate stability and TOC in macro-aggregates, and increases Al and Fe in all aggregates. Adoption of practices inclined to improve or maintain TOC as well as liming to increase pH are necessary management practices for sustainable production.

Characteristics and liming potential of biochar types from potato waste and pine-bark.

Large amount of wastes are burnt or left to decompose on site or at landfills where they cause air pollution and nutrient leaching to groundwater. Waste management strategies that return these food wastes to agricultural soils recover the carbon and nutrients that would otherwise have been lost, enrich soils and improve crop productivity. This study characterised biochar produced by pyrolysis of potato peels (PP), cull potato (CP) and pine bark (PB) at 350 and 650°C. The biochar types were analysed for pH, phosphorus (P) and other elemental composition. Proximate analysis was done following ASTM standard 1762-84, while surface functional groups and external morphology characteristics were determined using FTIR and SEM; respectively. Pine bark biochar had higher yield and fixed carbon (FC), and lower ash content and volatile matter than biochar types from potato wastes. The liming potential of CP 650°C is greater than that of PB biochars. Biochar types from potato waste had more functional groups even at high pyrolysis temperature relative to pine bark. Potato waste biochars showed an increase in pH, calcium carbonate equivalent (CCE), K and P content with increasing pyrolysis temperature. These findings imply that biochar from potato waste may be valuable for soil C storage, remediating acidity and increasing availability of nutrients especially K and P in acidic soils.

Land use and site effects on the distribution of carbon in some humic soil profiles of KwaZulu-Natal, South Africa.

Land use effects on the stocks of soil organic carbon (SOC) are generally based on the topsoil. Although subsoil horizons have lower concentrations, they contain a significant amount of SOC which may be more strongly protected than that in the topsoil layers. Analysis of SOC storage must therefore include the whole profile in respect of climate change mitigation. Humic soils in South Africa have high organic C in the A horizon, while the amount of C stocks through the whole profile depth is unknown. This study was conducted at six sites in KwaZulu-Natal Province to determine the effect of land use and site factors on C stocks, texture, pH and extractable aluminium (Al) and iron (Fe) concentrations and their vertical distribution to 100 cm in soils with thick (>45 cm) and thin (<45 cm) humic A horizons. The land use at some sites had been changed from grassland to maize and cultivated pasture and at others from forest to sugarcane farming. Cultivation with field crops reduced the organic C, mainly in the upper 20 cm (from 110 to 22 g C kg-1), with limited effect in deeper layers. The soils with thick humic A horizons and coarser texture stored more C in the deeper layers compared to those with thin humic A horizons and finer texture which had more of the C stocks in the 0-20 cm depth. Although cultivation reduced the soil C stocks in the surface layers, land use did not significantly affect the overall C stock (0-100 cm) at all sites. The high contents of extractable Fe (up to 340 mg kg-1) and Al (up to 3700 mg kg-1) stabilised the soil C and were more important than the effects of either land use or other site factors.

Short-term effects of selected organic fertilizer sources on carbon dioxide fluxes and soil quality.

Biogas slurry (BGS) has potential as an organic nutrient source, and understanding its effect on carbon (C) exchange in soils is important for clarifying the contribution of organic amendments to soil fertility and the C budget globally. This study evaluated the effect of BGS, cattle manure (CM), and chemical fertilizer (CF) on carbon dioxide (CO2 ) fluxes, microbial biomass C, and ß-glucosidase activity during the 2016-2017 and 2017-2018 maize (Zea mays L.) seasons, covering December-May, in South Africa. The experiment was arranged in a randomized complete block design with the treatments as (a) BGS, (b) CM, and (c) CF, applied at 40, 80, and 120 kg nitrogen (N) ha-1 . In both seasons, BGS and CM had higher CO2 fluxes than CF. Relative to CM, BGS resulted in higher CO2 flux earlier in the season and lower flux later in the season. The highest CO2 flux was in February but decreased as the season progressed. When expressed as a percentage of organic C present, CO2 fluxes increased with N rate for CM, decreased for BGS, and changed minimally for CF. At maize harvest, the microbial biomass C and ß-glucosidase activity were higher in CM than BGS at all N levels tested. These findings imply that relative to CF, applications of BGS and CM increase CO2 fluxes, soil organic C, microbial biomass C, and ß-glucosidase activity, and the two organic resources also differ in their contributions to CO2 fluxes, soil organic C, microbial biomass C, and ß-glucosidase activity depending on the part of the season, at least in the short term.

Sorption of Selected Heavy Metals with Different Relative Concentrations in Industrial Effluent on Biochar from Human Faecal Products and Pine-Bark.

The removal of heavy metals from effluents at source could reduce contamination of soil and water bodies. A batch sorption experiment was performed to determine the effects of feedstock of biochars pyrolysed at increasing temperature on sorption capacities of Cu, Cr and Zn from industrial effluent and aqueous solutions. Sewage sludge, latrine faecal waste and pine-bark biochars were used. The sorption data were fitted to the Langmuir isotherm. Maximum sorption capacities of latrine waste, sewage sludge and pine-bark biochar (350 °C) were, respectively, 313, 400 and 233 mg kg-1 for Zn, 102, 98.0 and 33.3 mg kg-1 for Cu, and 18.9, 13.8 and 67.1 mg kg-1 for Cr from industrial effluent. Conversely, sorption capacities from single metal solutions were 278, 227 and 104 mg Zn kg-1, 97.1, 137 and 21.3 mg Cu kg-1, 122, 106 and 147 mg Cr kg-1 on latrine waste, sewage sludge and pine-bark biochar, respectively. Step-wise regression analysis showed that the combined effects of ash, fixed C, pH influenced Zn sorption, ash and fixed C affected Cu sorption, and Cr sorption by ash and specific surface area of the biochar. The findings of the study imply that biochar from human faecal waste, particularly sewage sludge, has the potential to be utilized as sorbents of heavy metals from multiple metal effluent and that the sorption is affected by relative concentrations.

Biomass, Nitrogen Uptake and Content of Wolffia arrhiza Depends on Strength of Swine Lagoon Water.

Studies focusing on manipulation of growth conditions for duckweed Wolffia arrhiza to promote biomass for crop nutrient supply, are scarce. The effects of swine lagoon water (SLW) concentration and its replenishment and harvest regimes on selected properties of W. arrhiza were investigated. Dry matter and average growth rate of W. arrhiza were not affected by SLW replenishment periods, whereas the properties decreased with increasing concentration of SLW. The carbon and carbon/nitrogen content increased as the period between solution replenishment increased and as SLW concentration declined from 15 to 5%. Harvesting regimes did not affect the nitrogen content and uptake of duckweed, , and mineral-N of SLW. Harvesting duckweed once per week resulted in higher growth rate and biomass, compared with twice a week. Findings from this study suggest that W. arrhiza cultured on 10% SLW and harvested once a week yields biomass with nitrogen content suitable for crop nutrient supply.

Decomposition of Wolffia arrhiza residues rapidly increases mineral nitrogen and decreases extractable phosphorus in acidic soils.

While nutrient loads from anthropogenic sources upset aquatic ecosystem balance, Wolffia arrhiza (duckweed) has capacity to purge nutrient-rich water if continuously harvested. The nutrients accumulated in biomass have potential as soil fertility amendments. The objective of this study was to determine changes in release of nitrogen (N) and phosphorus (P), and the fate of P in soils after duckweed biomass amendment. An incubation experiment was conducted at 25 °C using three soils amended with proportions equivalent to 501, 1002 and 1503 mg N kg-1 and 62, 124 and 186 mg P kg-1. Soil samples were collected on 0, 3, 7, 14, 21, 28, 42 and 56 days, for ammonium-N, nitrate-N and extractable-P measurements. At the end of incubation, P pools were determined. At least 25 mg kg-1 of ammonium-N was released on day 0, reaching a peak within the first 2 weeks. Nitrate- and mineral-N increased from 14 to 42 days, with a corresponding decrease in ammonium-N. Relatively fertile soil released more mineral-N at higher applied ratios of duckweed than the less fertile. About 10-80 mg kg-1 of duckweed P was extractable on day 0 and amounts progressively declined over the incubation period. The combined percentage (0.5%) of tissue aluminium (Al) and iron (Fe) facilitated Al and Fe phosphate accumulation as the proportion of duckweed amendment increased. The results suggested that soil type and elemental composition of duckweed are important determinants for N and P release, and liming could improve P availability in soil.

Vermicomposting manure-paper mixture with igneous rock phosphate enhances biodegradation, phosphorus bioavailability and reduces heavy metal concentrations.

In organic soil fertility management, rock phosphate (RP) is gaining momentum as an acceptable phosphorus source, though much of this P is not bioavailable for plant uptake, particularly in igneous RP. This study evaluated the nutrient solubilization, biodegradation and heavy metal concentration when cow dung - waste paper mixture amended with increasing rates of igneous RP was vermicomposted with E. fetida. The cow dung was optimized to a C/N ratio of 30 using waste paper and amended with RP to provide 0%; 2%; 4% and 8% of elemental phosphorus on a dry w/w basis. Incorporation of RP at 2% and 8% P enhanced compost biodegradation resulting in a 12% and 22% significantly (P < 0.001) lower final C/N ratio, respectively, compared to the control; together with higher humification parameters. Amending the cow dung - waste paper mixture with 2%, 4% and 8% P as rock phosphate, resulted in a 39%; 50% and 65% more resin extractable P, respectively, relative to the control. Similarly, the bicarbonate extractable P, which represents the bioavailable P fraction, increased consistently by 19%; 28% and 33% following 2%, 4% and 8% RP application, respectively. Though incorporation of RP initially resulted in increased heavy metal levels, reductions of 40%; 35%; 35%; 40% and 45% for Cr, Cu, Cd, Pb and Zn, respectively, were observed in the 8% RP treatment after 8 weeks, due to the presence of earthworms. Vermicomposting with E. fetida significantly reduced heavy metals to levels below the maximum permissible concentration of potentially toxic elements in soils after 8 weeks. This study demonstrates the potential of optimized vermicomposting with igneous RP for generating nutrient rich organic fertilizers.

Effects of a precomposting step on the vermicomposting of dairy manure-waste paper mixtures.

Thermophilic composting is being promoted as a means of sanitizing waste materials prior to vermicomposting. The precomposting duration is, however, critical to the success of the vermicomposting phase as it affects worm biomass. This study evaluated the effectiveness of different precomposting periods (0, 1, 2, 3 and 4 weeks) on the sanitization and vermicomposting of dairy manure-waste paper mixtures. The parameters measured were coliform bacteria and protozoa oocyst numbers, earthworm growth, as well as stabilization and nutrient content of vermicomposts. Over 95% of fecal coliforms, Escherichia coli and of E. coli 0157 were eliminated from the waste materials within 1 week of precomposting and total elimination of these and protozoan oocysts was achieved after 3 weeks of precomposting. Microbial biomass carbon and water soluble carbon of waste mixtures decreased with increase in precomposting time and impacted negatively on earthworm growth and subsequent stabilization of the dairy manure-paper waste mixtures. Vermicomposts from waste mixtures precomposted for over 2 weeks were less stabilized, less humified and had lower nutrient contents than vermicomposts from waste mixtures precomposted for 1 week or less. A precomposting period of 1 week was found to be ideal for the effective vermicomposting of dairy manure-waste paper mixtures.

Complementary nutrient effects of separately collected human faeces and urine on the yield and nutrient uptake of spinach (Spinacia oleracea).

A glasshouse experiment was conducted to evaluate the combined use of separately collected human faeces and urine as fertilizer for spinach (Spinacia oleracea) production. Seven human faeces N : urine N combinations (1 : 7 to 7 : 1) each supplying 200 kg N ha(-1) were evaluated along with sole human faeces, sole urine, inorganic fertilizer and an unamended control. Complementary application of the two resources, human faeces and urine, increased fresh and dry matter yields only in treatments having high proportions of urine. Nitrogen uptake followed the same trend but the opposite trend occurred for P uptake indicating that urine was a better source of N whereas human faeces were the better source of P. Potassium uptake was not influenced by the two resources. The minimal improvement observed in the fertilizer value of human faeces when co-applied with urine suggested that co-application of the two resources may not give an added yield advantage when compared with sole human faeces.

Evaluation of human urine as a source of nutrients for selected vegetables and maize under tunnel house conditions in the Eastern Cape, South Africa.

The introduction of ecological sanitation (ECOSAN) toilets in South Africa has created opportunities for safer sanitation and recycling of human excreta, as fertilizers, in rural and peri-urban areas. A study was carried out to evaluate the fertilizer value of human urine (0 to 400 kg N ha(-1)) for maize and tomato, compared to urea, in a tunnel house. Dry matter yield of both maize and tomato, harvested at 9 and 10 weeks after planting, respectively, increased with increasing N rate (both as urine or urea) up to 200 kg N ha(-1). Urea reduced soil electrical conductivity (EC) whereas urine increased it. Leaf tissue Na, in both crops, also increased with urine application. A follow-up study was carried out with two crops with contrasting sensitivity to salinity and using a wider range of N application (0 to 800 kg N ha(-1)). The results indicated increased root and leaf dry-matter yield of beetroot (tolerant to salinity) with increased urine rates up to the highest rate of 800 kg N ha(-1), whereas the leaf and root dry-matter yield of carrot, which is sensitive to salinity, peaked at the low urine application rate of 50 kg N ha(-1). Soil EC increased with urine application up to 4.64 and 13.35 mS cm(-1), under beetroot and carrot, respectively. Generally the results showed that human urine compared well with urea as a source of N for crops but optimum rates depend on the sensitivity of the crops to soil salinity, which should be monitored where human urine is regularly used for fertilizing crops.