No abstract

Contact CEH NORA team at noraceh@ceh.ac.ukThe NERC and CEH trademarks and logos ('the Trademarks') are registered trademarks of NERC in the UK and other countries, and may not be used without the prior written consent of the Trademark owner.

Heat-treated animal bone char (ABC) has not previously been evaluated for its potential as a phosphorus (P) fertilizer. ABC, Gafsa phosphate rock (GPR) and triple superphosphate fertilizer (TSP) were incubated in 12 soils. Dissolved-P was assessed by extraction with NaOH and bioavailability with the Olsen extractant. The rate of P dissolution from ABC was described almost equally well by the Elovich and Power equations. After 145 days, the fraction of P dissolved ranged from 0 to 73% and to 56% for ABC and GPR, respectively. The most important soil properties determining P dissolution from ABC were pH and P sorption. P dissolution was not significant at soil pH [6.1 (ABC) and [5 (GPR) and the lower the pH, the greater the Dissolved-P. Dissolved-P also correlated positively and significantly with inorganic P sorption, measured by the Freundlich isotherm and the P sorption index of Bache and Williams (1971). Soil pH and P sorption index could be combined in multiple regression equations that use readily measured soil properties to predict the potential for ABC dissolution in a soil. Dissolution of P from GPR correlated with soil pH and exchangeable acidity. In comparison with GPR, ABC was a better source of available P, assessed by Olsen-P. In most soils, ABC increased Olsen-P immediately after application, including soils of relatively high pH in which GPR was ineffective. ABC is a P fertilizer of solubility intermediate between GPR and TSP.

Cocoa pod husk (CPH) is the main by-product (ca. 70-75% weight of whole fruit) of the cocoa harvest, an important and economic crop in developing countries. It is a rich source of minerals (particularly potassium), fibre (including lignin, cellulose, hemicellulose and pectin) and antioxidants (e.g. phenolic acids). An existing practise is the return of CPH to soil with potential benefits (or disadvantages) for cocoa productivity and soil sustainability that have not been fully characterised. Currently, alternative low-value applications of CPH include its use as animal feed, as a starting material for soap making and activated carbon. Other biotechnological valorisation potentials for CPH and its fractions include the production of bio-fuels and their incorporation in food systems. Physical, chemical or biological pretreatment approaches are needed in order to achieve desirable fractions in a cost-effective and sustainable manner for novel applications in food and non-food sectors.

A model for the turnover of organic matter in soil, ROTHC‐26.3, can be used to calculate how much organic C needs to enter a soil annually in order to maintain a specified stock of soil organic C. The annual return of organic C thus calculated, plus the amount of organic C removed annually from the site by harvesting, burning, etc., provides an estimate of the Net Primary Production (NPP) of that site, averaged over many years. The new method was used to calculate NPP for two adjacent savanna sites in the Nairobi National Park in Kenya, one grazed and one not, and for a dry Miombo woodland site in Zambia. Both the Kenyan and Zambian sites are taken to be at equilibrium, with soil organic C levels at steady state. Soils from the three sites were analyzed by layer for organic C, δ14C, δ13C, soil microbial biomass C, total N, pH, and clay content. Radiocarbon measurements were >100% modern in the surface layers (0–15 cm) of the Kenyan soils (both Vertisols) and in all three layers (0–15, 15–30 and 30–50 cm) of the Zambian soil (an Oxisol), presumably because of 14C coming from the testing of thermonuclear bombs. The 15–30 cm layer of the Kenyan soils dated at ∼500 yr and the 30–50 cm layer at ∼900 yr. The 14C data were consistent with the presence of a small inert fraction of organic C that accounted for an increasing proportion of total organic C with increasing soil depth. The 13C data indicated that the Kenyan soils had developed under C4 vegetation, whereas the Zambian soils had developed under vegetation dominated by C3 plants. From these results the annual input of C to soil from the ungrazed Kenyan site was calculated to be 388 g C·m−2·yr−1, to the grazed site 380 g C·m−2·yr−1, and to the Zambian soil 373 g C·m−2·yr−1. Taking the loss of C from the Kenyan sites by burning to be 40 g C·m−2·yr−1, the mean NPP for both Kenyan sites is 424 g C·m−2·yr−1. This value for NPP is compatible with earlier estimates of NPP by botanical methods from the same site in Kenya. Wood‐taking is thought to be minimal in the protected Zambian woodland, so that here the annual input of C to the soil can be taken as the NPP without great error. This new method provides a long‐term, integrated measure of NPP that should complement and enhance productivity measurements made by harvest methods over shorter periods.

No abstract

Accumulation of surplus phosphorus (P) in the soil and the resulting increased transport of P in land runoff contribute to freshwater eutrophication. The effects of increasing soil P (19-194 mg Olsen-P (OP) kg À1 ) on the concentrations of particulate P (PP), and sorption properties (Q max , k and EPCo) of suspended solids (SS) in overland flow from 15 unreplicated field plots established on a dispersive arable soil were measured over three monitoring periods under natural rainfall. Concentrations of PP in plot runoff increased linearly at a rate of 2.6 mg litre À1 per mg OP kg À1 of soil, but this rate was approximately 50% of the rate of increase in dissolved P (< 0.45 mm). Concentrations of SS in runoff were similar across all plots and contained a greater P sorption capacity (mean þ 57%) than the soil because of enrichment with fine silt and clay (0.45-20 mm). As soil P increased, the P enrichment ratio of the SS declined exponentially, and the values of P saturation (P sat ; 15-42%) and equilibrium P concentration (EPCo; 0.7-5.5 mg litre À1 ) in the SS fell within narrower ranges compared with the soils (6-74% and 0.1-10 mg litre À1 , respectively). When OP was < 100 mg kg À1 , P sat and EPCo values in the SS were smaller than those in the soil and vice-versa, suggesting that eroding particles from soils with both average and high P fertility would release P on entering the local (Rosemaund) stream. Increasing soil OP from average to high P fertility increased the P content of the SS by approximately 10%, but had no significant (P > 0.05) effect on the P sat , or EPCo, of the SS. Management options to reduce soil P status as a means of reducing P losses in land runoff and minimizing eutrophication risk may therefore have more limited effect than is currently assumed in catchment management.

No abstract