Enhanced-efficiency phosphate fertilisers, diffusive flux of phosphorus and matric potential in Acrudox

Enhanced-efficiency phosphate fertilisers may play an important role in phosphorus (P) availability in tropical soils by increasing their concentration in solution and enhancing the diffusive flux of P (DFP). This work evaluated the DFP in soil influenced by polymer-coated phosphate fertilisers and organophosphates (enhanced-efficiency phosphate fertilisers) applied to soil, at two matric potentials. The experiment was conducted using a 4 × 2 × 4 + 2 factorial design in which four phosphate fertilisers (conventional monoammonium phosphate (MAP), polymer-coated monoammonium phosphate (POL), pelletised monoammonium phosphate with filter cake (FC) and granulated monoammonium phosphate with swine compost (SC)), two soil water contents corresponding to two matric potentials (–10 and –50 kPa), four anion exchange resin insertion distances (0.5, 1.0, 1.5 and 2.0 cm from the phosphate fertiliser granules) and two control treatments (matric potential of –10 and –50 kPa without fertiliser) were studied across four replicates. Enhanced-efficiency phosphate fertilisers increased the release of P into the soil solution. The values of DFP (nmol m–2 15 days–1) for MAP were in the range of 0.18–48.69, for POL were 0.19–32.20, for FC were 0.17–19.74 and for SC were 0.17–18.50. For –10 and –50 kPa matric potentials, the values ranged within 0.18–43.07 and 0.17–48.69 nmol m–2 15 days–1 respectively. In relation to the distances 0.5, 1.0, 1.5 and 2.0 cm, DFP (nmol m–2 15 days–1) ranged within 17.56–48.69, 0.42–11.39, 0.22–0.57 and 0.17–0.22 respectively. The decrease in the soil water matric potential decreased DFP in the short term for fertilisers with coating technologies compared to MAP. This result indicates that coating technologies hold promise for maintaining DFP over time.

Partial Nutrient Balances in Tropical Velvet Bean-Maize System in Zimbabwe

In a field experiment on legume-maize cropping sequence, the effect of nitrogen and phosphate fertiliser application on nutrient budgeting after a two year cropping cycle was studied. The results of this work showed that partial nutrient balances can give an indication about the sustainability of a system unless a full stock of all the nutrients is known. It is also clear from these results that there would unlikely be a carryover of N to the next season, probably due to leaching of N from the top soil. Positive partial P balances would, on the other hand, be of residual value. However, it should be noted that the positive partial P balances were only observed where maize yield was low. The long-term perspectives of a crop production system cannot be assessed solely on the basis of partial nutrient balances. The nutrient stock: balance ratio may be a better indicator of sustainability, giving a more accurate indication of how long farming can continue in the same way, given the available nutrients. These points towards taking a fresh look at the existing recommended application rates for maize crops.

The relative strengths of phosphate fertiliser application and white clover cultivar introduction for hill pasture improvement

Combinations of four phosphorus (P) fertiliser rates (0, 8.5, 22.5 or 26.5 kg/ha/year of citrate-soluble P) and three pasture types with different white clover germplasm, 'resident' cv. Huia and cv. Tahora were compared in self-contained, replicated farmlets grazed by sheep over 4 years. Fertiliser increased white clover herbage accumulation (HA) 3- to 4-fold compared with the control treatment, and increased total sward HA by 50%. Introduction of Tahora white clover significantly increased white clover and total sward HA and nitrogen fixation compared with the resident and Huia-sown swards. Sheep liveweight gain was significantly greater in all systems fertilised with P (438 versus 243 kg/ha for the unfertilised control) and in systems sown with Tahora (425 versus 372 kg/ha for resident and Huia). Keywords: phosphorus fertiliser, white clover, cultivars, herbage accumulation, animal production