Agroecological analysis and economic benefit of organic resources and fertiliser in till and no-till sorghum production after a 6-year fallow in semi-arid West Africa

A field experiment was conducted in Gampela (Burkina Faso) in 2000 and 2001 to assess the impact of organic and mineral sources of nutrients and combinations thereof in optimising crop production in till and no-till systems and to assess the economic benefit of these options. The study showed that under conditions of rainfall deficiency, the use of a single organic resource at an equivalent dose of 40 kg N ha⁻¹ better secured crop yield than the application of an equivalent amount as urea-N, while a combination of organic resources and fertiliser was better in increasing crop yield than the application of the same N amount in the form of urea. In a year of rainfall deficiency, a mix of organic resources and fertiliser in both till and no-till systems increased crop water use efficiency, with the result that the farmer was able to purchase only half of the normal quantity of N fertiliser to obtain a higher yield that he would have done when all of the N was supplied in the form of urea. Under conditions where soil N is deficient, an economic benefit was achieved when urea was combined with easily decomposable organic material (e.g. sheep dung); mixing the urea at a dose of 40 kg N ha⁻¹ with maize straw was not sufficient in alleviating the negative interaction due to the enhanced N immobilisation. The results demonstrate that the use of N fertiliser alone was risky and that a higher yield, with the accompanying economic benefit, was scarcely achieved under the prevailing rainfall conditions. The application of soil and water conservation measures can contribute greatly to increasing the economic benefit of mineral, organic or combined organic and mineral-derived nutrient application under semi-arid conditions.     

Compositional changes in the hydrophobic acids fraction of drainage water from different land management practices

Dissolved organic matter (DOM) can play a key role in many environmental processes, including carbon cycling, nutrient transport and the fates of contaminants and of agrochemicals. Hydrophobic acids (Ho), the major components of the DOM, were recovered from the drainage waters from well-drained (WDS) and poorly-drained (PDS) Irish grassland soils in lysimeters, amended with N fertiliser (F) and with bovine urine (U) and were studied using 1D and 2D solution-state Nuclear Magnetic Resonance (NMR) spectroscopy. The Diffusion Edited (DE) ¹H NMR spectra indicated that the Ho consisted largely of larger molecules, or of molecules that formed rigid aggregates, and the 1D and the 2D (Heteronuclear Multiple Quantum Coherence - HMQC, the Total Correlation Spectroscopy - TOCSY, and the Nuclear Overhauser Effect - NOESY) spectra indicated that the samples were composed of lignin residues, carbohydrates, protein/peptides, and aliphatic components derived from plant waxes/cuticular materials and from microbial lipids. The F amendments increased the concentrations of Ho in the waters by 1.5 and 2.5 times those in the controls in the cases of WDS and PDS, respectively. The lignin-derived components were increased by 50% and 300% in the cases of the Ho from the WDS and PDS, respectively. Applications of F + U decreased the losses of Ho, (compared to the F amendments alone) and very significantly decreased those of the lignin-derived materials, indicating that enhanced microbial activity from U gave rise to enhanced metabolism of the Ho components, and especially of lignin. In contrast the less biodegradable aliphatic components containing cuticular materials increased as the result of applications of F + U. This study helps our understanding of how management practices influence the movement of C between terrestrial and aquatic environments.     

Crop responses to 15N-labelled organic and inorganic nitrogen sources

A major challenge for low-external-input farming systems is to secure the N supply. Lack of synchrony between mineralization of organic N sources and plant N requirements is causing many growers to use different techniques to overcome this problem. One of these techniques is the application of soluble water extracts of different farm residues and plants. A field study was conducted to study the crop uptake of applied ¹⁵N-labeled alfalfa and clover extracts as compared to the N uptake from¹⁵N-glycine and three levels of ¹⁵N-(NH₄)₂SO₄. The results show that total N accumulation in the field crops, squash and lettuce was primarily affected by the amount of added N (P ≤ 0.05) and not by the form in which the N was applied (P ≤ 0.05). The utilization efficiencies of N (pNdff) from plant extracts and glycine increased (P ≤ 0.05) gradually from 10, 20, to 30 days after application in contrast to (NH₄)₂SO₄ which peaked in utilization efficiencies of 56% around 20 days after application. The pNdff reached 60%, 40% and 36% of the applied glycine, alfalfa and clover extracts, respectively in lettuce. Squash showed the same pattern during at 10, 20 and 30 days; however, the proportion of N derived from most of the treatments was higher in squash than in lettuce (P ≤ 0.05). These results indicate that plant extracts of clover and alfalfa can be used as efficient N fertilisers in low-external-input agroecosystems.     

Reuse of urban wastewater treated by a combined stabilisation pond system in Benslimane (Morocco)

The aim of this paper is to study the performance of a combined waste stabilisation pond after three years of functioning and the reuse of treated wastewater for irrigating potatoes and lettuce culture. The combined ponds showed good functioning conditions and excellent performances either for organic load (90%), faecal coliform (6 log units) or helminth eggs (100%) and produced a high and perennial effluent quality. The effluent could be used for non-restrictive irrigation, with a clear improvement of culture production and hygienic quality for both fruits and soil.     

Are groundwater nitrate concentrations reaching a turning point in some chalk aquifers?

In past decades, there has been much scientific effort dedicated to the development of models for simulation and prediction of nitrate concentrations in groundwaters, but producing truly predictive models remains a major challenge. A time-series model, based on long-term variations in nitrate fertiliser applications and average rainfall, was calibrated against measured concentrations from five boreholes in the River Frome catchment of Southern England for the period spanning from the mid-1970s to 2003. The model was then used to “blind” predict nitrate concentrations for the period 2003-2008. To our knowledge, this represents the first “blind” test of a model for predicting nitrate concentrations in aquifers. It was found that relatively simple time-series models could explain and predict a significant proportion of the variation in nitrate concentrations in these groundwater abstraction points (R² = 0.6-0.9 and mean absolute prediction errors 4.2-8.0%). The study highlighted some important limitations and uncertainties in this, and other modelling approaches, in particular regarding long-term nitrate fertiliser application data. In three of the five groundwater abstraction points (Hooke, Empool and Eagle Lodge), once seasonal variations were accounted for, there was a recent change in the generally upward historical trend in nitrate concentrations. This may be an early indication of a response to levelling-off (and declining) fertiliser application rates since the 1980s. There was no clear indication of trend change at the Forston and Winterbourne Abbas sites nor in the trend of nitrate concentration in the River Frome itself from 1965 to 2008.     

A conceptual framework for determining economically optimal fertiliser use in oil palm plantations with factorial fertiliser trials

The theory, and the statistics and mathematics of using factorial fertiliser trials to assist in making fertiliser recommendations for neighbouring commercial plantings is presented as a conceptual framework and in a format for practical application. As an example, the yield and leaf nutrient levels from a typical factorial fertiliser rate trial (nitrogen by potassium) were modelled using multiple linear regression and the resulting response surfaces used to determine the maximum agronomic yield and optimum economic yield and to calculate the requirement for ‘basal’ fertiliser. Leaf nutrient data in both the trial and commercial plantings was used to estimate the requirement for ‘corrective’ fertiliser, where necessary, to increase the leaf nutrient levels to the target leaf nutrient level for maximum yield. All the mathematics required can be incorporated into a spreadsheet calculator that uses costs (e.g. fertiliser) and prices (e.g. oil) to calculate optimum economic fertiliser application rates. Problems with extrapolating the results of fertiliser trials to commercial plantings can be overcome by matching each trial with a corresponding commercial planting domain.     

The influence of two soil nitrogen levels on the utilisation of 15N-labelled ammonium nitrate by ryegrass

In a field plot experiment with grass under cutting management, two soil organic nitrogen levels (0.92% and 1.14% in the top 75mm of soil) were created by repeated applications of pig slurry over a period of 8 years. The influence of soil organic nitrogen level on the recovery by ryegrass of ammonium nitrate fertiliser was then studied by reseeding the plots and applying ¹⁵N-labelled fertiliser at four rates (40, 80, 120, 160kg N ha^?1). After each of the first four cuts unlabelled ammonium nitrate fertiliser was applied at these same rates. The percentage utilisation of the labelled fertiliser was measured in five harvests over 2 years. At the first cut the percentage utilisation averaged 46.4% and was independent of fertiliser rate and soil organic nitrogen level. The average percentage utilisation values in cuts 2, 3, 4 and 5 were 9.9, 2.4, 0.8 and 0.5 respectively. For the total of all cuts it was only at the 40 kg N ha^?1 fertiliser rate that the percentage utilisation was significantly different (P<0.05) between the 0.92% and 1.14% soil organic nitrogen levels, at 49.0% and 61.4% respectively. The soil nitrogen contribution to ryegrass at the first cut was significantly increased (P<0.05) by the high soil organic nitrogen level at the 40 and 160 kg N ha^?1 fertiliser rates. Over all fertiliser rates the average soil nitrogen contribution to the first cut was 50.4 and 61.1 kg N ha^?1 at the 0.92 and 1.14% soil organic nitrogen levels respectively. From the first cut data, soil organic nitrogen was estimated to have a net mineralisation rate of 2.6% year^?1 and a half-life of 26 years.     

The effect of hygienic treatment on the microbial flora of biowaste at biogas plants

In Sweden, full-scale, commercial biogas plants (BGP), which process low-risk animal waste, operate a separate pre-pasteurisation at 70 °C for 60 min as required by EEC regulation 1774/2002. The purpose of this study was to establish if, during pasteurisation and further processing and handling in full-scale BGPs, pathogens in biowaste could be sufficiently reduced to allow its use on arable land.

Four BGPs were sampled on six occasions during 1 year. Sampling was performed from six locations during biogas production. The samples being analysed quantitatively to detect indicator bacteria (Escherichia coli, Enterococcus spp. and coliforms) and spore-forming bacteria (Clostridium spp. and Bacillus spp.) and qualitatively for bacterial pathogens (salmonella, listeria, campylobacter and VTEC O157).

Salmonella was the most frequently isolated pathogen before pasteurisation In general, the treatment adequatly reduced both indicator and pathogenic bacteria. Spore-forming bacteria were not reduced. However, recontamination and regrowth of bacteria in biowaste was frequently noted after pasteurisation and digestion.     

Evaluation of partially acidulated phosphate fertilisers and reactive phosphate rock for hill pastures

The initial and residual effectiveness of two partially acidulated fertilisers, a single superphosphate (SSP): reactive phosphate rock (RPR) physical mix (SSP:RPR) and a partially acidulated phosphate rock (PAPR), and a RPR, North Carolina, were compared with SSP at two phosphate (P)-responsive sites in hill country. One site had received small annual inputs of SSP (125 kg ha^–1 y^–1) fertiliser for 10 years (LF) and the other site no SSP in the past 5 years (NF). The SSP, PAPR and RPR were applied at 3 rates (20, 40 and 60 kg P ha^–1) and SSP:RPR at one rate (40 kg P ha^–1) once only in the first year. Fertiliser treatments were applied with or without Grasslands Huia white clover (Trifolium repens L.) seed. Initial and residual pasture and legume responses were measured over two years.In the first year, pasture and legume response to applied P was much greater at the LF than NF site. A deterioration in legume content and vigour brought about by withholding fertiliser, rather than a difference in soil-fertiliser reactions, appears to be the main reason for the different response at the two sites in the first year. At the LF site the fully (SSP) and partially (SSP:RPR and PAPR) acidulated fertilisers were far more effective in stimulating legume growth than the RPR, while at the NF site no differences in pasture or legume production were found between fertilisers in the first year. Where fertiliser has been withheld for a number of years the use of SSP appears to be a wasteful and inefficient use of a processed fertiliser.Residual effects of RPR were greater than those of SSP, as shown by the greater yield of legume at both sites in the second year. The residual effectiveness of both the partially acidulated materials was much less than that of the RPR. Mixing and sowing white clover with the fertilisers had some beneficial effects on legume content at the NF site in both years and improved legume production at this site in the second year.     

The influence of organic and inorganic fertiliser application rates on UK biomass crop sustainability

Bioenergy and energy crops are an important part of the UK’s renewable energy strategy to reach its greenhouse gas reduction target of 80% by 2050. Ensuring the sustainability of biomass feedstocks requires a greater understanding of all aspects of energy crop production, their ecological impacts and yields. This work compares the life-cycle environmental impact of natural gas and biomass from two energy crop systems grown under typical UK agronomic practice. As reported in previous studies the energy crops provide significant reductions in global warming potential (GWP) compared to natural gas. Compared to no fertiliser application, applying inorganic fertiliser increases the GWP by 2% and applying sewage sludge increases the GWP by a lesser extent. In terms of an equivalent GWP savings per unit area of land, the emissions associated with fertiliser production and application can be offset by a yield increase of <0.2 t/ha. However, very large increases in eutrophication and acidification levels are incurred compared to the natural gas reference case when applying either fertiliser. For sewage sludge the impact of varying the allocation factor between the function of wastewater treatment and that of crop growth is also illustrated.