W. van Averbeke

Nitrogen mineralization potential of three animal manures applied on a sandy clay loam soil

Understanding the dynamics of N forms applied as manure is germane for appropriate rate and timing of applications of manure. Manure characterization and laboratory incubation were conducted for 120 days to study the mineralization of poultry, cattle and goat manures. Results showed that manure properties differ. Net immobilization of N was recorded for goat and cattle manures while poultry manure mineralized marginally. The relationship between N release and time is polynomial (cubic). The release phases were: initial rapid N release at 0-30 days; phase of constant release; 40-55 days; decline phase in N release 70-90 days and sharp increase in N release at 120 days. Increasing the N rates of manures above 120 kgNha(-1) will improve their potential as plant nutrient sources. Complementing the manures with inorganic N fertilizers in integrated nutrient management will also improve its quality and effectiveness.

Mineralogy and Fertility Status of Selected Soils of the Eastern Cape Province, South Africa

Abstract Thorough knowledge of cultivated soils is necessary for their informed and sustainable management. This study was carried out to gain a better understanding of cropped soils in the Eastern Cape Province of South Africa. The mineralogical and chemical composition and nutrient status of topsoils collected from homestead gardens and fields of smallholdings in 5 of the 36 magisterial districts where smallholder farming prevails in the Province were determined. These data were supplemented with results of soil analyses conducted by an Analytical Services Laboratory that obtains its samples from the 31 magisterial districts where large‐scale farms are dominant. The soils studied were similar mineralogically, and all had a clay fraction that was dominated by quartz, mica, and/or kaolinite, which is fairly typical for many tropical and subtropical soils. Elemental analysis showed that the soils were generally low to very low in their total content of nutrients, except for sulfur (S), manganese (Mn), zinc (Zn), copper (Cu), and boron (B), reflecting the marine and sedimentary nature of their parent materials. The available nutrient status of the cultivated soils was generally low to very low, especially those found in smallholder fields. This was attributed to low soil organic matter levels and low geological reserves of some nutrients notably phosphorus (P), potassium (K), and calcium (Ca), coupled with continuous cultivation of the lands without adequate nutrient replenishment. Depending on location, 75–100% of the fields tested low in pH, 62–100% were low in organic carbon, 83–100% were low in extractable K, 62–93% were low in extractable Ca, and 79–100% were deficient in available phosphorus. The nutrient status of soils receiving moderate to high amounts of nutrients was generally satisfactory, as revealed by the nutrient content of garden soils found on smallholdings and the fields on large‐scale farms. In all cases, soil pH was low to critically low. The findings are used to propose a soil fertility management strategy for the communal areas of the Province.

Smallholder farming styles and development policy in South Africa: The case of Dzindi Irrigation Scheme

Abstract Diversity among smallholders farming 1.28 ha plots at Dzindi Irrigation Scheme in the Thulamela Local Municipality of Limpopo Province, South Africa is investigated by applying farming style theory. Farming styles refer to specific farming strategies, which are conscious responses of farmers to the prevailing ecological and socio-economic conditions. The specific objectives of the study were to identify and characterize styles of farming in the Dzindi community of smallholders, to provide an understanding of the different styles from a smallholder perspective, and to interpret the meaning of the findings for smallholder development policy. Data collection involved both quantitative and qualitative methods. Three main farming styles were identified, and in each of these farmers employed particular strategies, which were congruent with their farming objectives, and which represented different degrees of exposure to risk evidenced by the crop selection, the amount of land they planted, the service providers they used with specific reference to land preparation, the social networks they maintained, especially with regard to marketing produce, the labour they hired and the farming requisites they purchased and utilised. The findings suggest that the response by farmers in the different styles to contemporary agricultural and related policy aimed at their empowerment and commercialisation is unlikely to be uniform, and this is expected to dilute the impact of policy measures in support of specific development trajectories.

Fate of manure phosphorus in a weathered sandy clay loam soil amended with three animal manures.

Laboratory incubation was conducted for 120 days to study the fate of phosphorus in poultry (PM), cattle (CM) and goat manures (GM). Phosphorus mineralized from manure was dependent on total P, Al and Fe content. Manures improved P availability in the order: PM>CM>GM; however, the highest amount of P was fixed or immobilized between 10 and 70 days of incubating with CM and GM. Fixation and immobilization of mineralized P from poultry manure was negligible probably due to the high total P and the low amount of Al and Fe. Generally, manure application reduced the ability of the soil to fix P. More than 90% of the manure P was either immobilized or fixed by the soil. The relationship between the amount of P released and time was cubic. Improvement of the C:P ratio of CM and GM would be an option to enhance their agronomic use as fertilizer P source.

Effect of irrigation scheduling on leaf yield of non-heading Chinese cabbage (Brassica rapa L. subsp. chinensis).

A field experiment conducted on the Dzindi canal irrigation scheme in the north of South Africa demonstrated that non-heading Chinese cabbage (Brassica rapa L. subsp. chinensis) needed to be irrigated at least twice per week to maintain the water content of the rooting zone close to field capacity and achieve maximum leaf yield. Irrigation scheduling practice affected both total consumptive water use and leaf yield of the crop and the latter two variables were strongly correlated (r = 0.91). Single applications of 20 mm per week, commonly practiced by smallholders on canal irrigation schemes in the region, limited yield to about two-thirds of the maximum achieved when the soil was irrigated to field capacity every other day. Pre-charging the upper 800 mm of the soil profile to field capacity followed by single applications of 20 mm per week increased yield, but only to 80% of the maximum, suggesting that the scope for improving water use efficiency in non-heading Chinese cabbage through the use of deficit irrigation was limited.

Dynamics of Soil pH and Electrical Conductivity with the Application of Three Animal Manures

A laboratory incubation experiment was conducted to determine the dynamics of soil pH and electrical conductivity (EC) in a soil to which three animal manures [poultry (PM), cattle (CM), and goat (GM) manures] had been applied. The result of this study showed that the manures differed in qualities. Poultry manure had significantly greater EC and dissolved salts compared with the other manures, whereas the pH of cattle and goat manures are significantly greater than that of PM treatment. The liming effect of the manures was only for about 30 days after manure incorporation, and it varied with manure type and incubation period. There was an increase in EC as days of incubation increased. The potential of manure-induced soil salinization is very high in PM and GM. It was concluded that manure quality and use should be synchronized with consideration of their liming potential and reduced salinization effect.

Pine litter as substrate for propagation of vegetable transplants in trays

The study evaluates the potential of pine litter for use as a substrate in the propagation of vegetable transplants in trays. Sub-optimum pH and electrical conductivity of pine litter were addressed by incorporating 10% feedlot manure by volume. The water holding capacities of pine litter and the pine litter-feedlot manure mixture were higher than the minimum required, but their air filled porosities were below optimum. The pine litter-feedlot manure mixture reduced the germination percentages of cabbage seedlings by 17% and lettuce seedlings by 13% relative to composted pine bark, but the germination percentage of tomato seedlings was similar in both substrates. There were no significant differences in the growth of vegetable transplants between the two substrates. In both substrates increasing nutrient availability by adding controlled-release fertilizer had similar positive effects on the growth transplants. Substrate-nutrient availability interactions were only observed in dry shoot mass of lettuce seedlings and dry root mass of tomato seedlings. Composting the pine-litter animal manure mixture could possibly improve the observed low germination percentage of vegetable transplants in pine litter.

Salinity Effect of Animal Manure on Leafy Vegetable Yield

Crop produce maximum yield at optimum fertiliser level. Excess nutrient in soil limits germination, growth and yield. Efficient use of manure requires persistent development to enable recommendation for its safe application rate. To this end, this research evaluated the effect of salinity from different application rates of manure on yield of vegetables. Green house and laboratory assays were used for vegetable growth and the determination of electrical conductivity (EC), respectively. Salinity effect on plant growth occurred to be a function of manure type. Optimum salinity level of poultry manure ranged from 15.6 to 21.8 mS m–1 EC. For goat manure, optimum EC ranged from 29.1 to 59.2 mS m–1. For cattle manure, EC was about 42.3 mS m–1 but for Chinese cabbage, the highest biomass was obtained at the highest EC of 47.4 mS m–1. Salinity differed considerably among manures.

Effects of liming on microbial activity and N mineralization in broiler manure-amended soils from Bizana, Eastern Cape, South Africa.

A laboratory incubation study was conducted to determine the effects of liming on microbial activity and N mineralization in two Bizana soils amended with broiler manure. The experimental layout was a 4 x 3 complete factorial experiment with three replicates, arranged in a randomized design. Soil pH, CO2 evolution, and mineral N concentration were measured. After 56 days the soil pH ranged from 4.50 to 5.74 and 4.99 to 5.94, in the Magusheni and Nikwe soils, respectively. The effect of liming on microbial activity and N mineralization differed between the soils. In the Nikwe soil (acid saturation 4.0%), microbial activity and N mineralization increased as the rate of broiler manure application was raised, but liming had no effect. In the Magusheni soil (acid saturation 25%), microbial activity increased as both lime and chicken manure application rates increased, but liming reduced N mineralization, suggesting N immobilization was being driven by an active microbial population in the limed soils. The rates of lime and/or chicken manure application, percentage Ca2 + and soil acid saturation were important factors influencing microbial activity and N mineralization, but the effect of soil pH on N mineralization was not evident in either of the soils.