Constructing a nitrogen fertilizer recommendation system using a dynamic model: what do farmers want?

Abstract. An effective fertilizer recommendation system requires information on seasonal, soil-related and cultural variations in soil mineral nitrogen (N) and nutrient requirements of the crop. This can be provided by dynamic N turnover models, such as listed by Plentinger & Penning De Vries (1996). In this paper, we describe a survey of farmer opinion designed to ascertain what farmers want from such a decision support system. Over 100 farmers were surveyed. Surveyed farmers requested that default values be available for all model inputs. Inputs should be entered both by windows-based menu (for clarity) and tabular format (for speed), have user-selected units, and be fully supported by context-sensitive help. The system should have a hierarchical structure allowing access to fixed parameters, and be compatible with commonly used farm recording packages. Recommendations should be provided both for the field (single and optional application rates), and in tabular format across the whole farm. Simulations should be easily rerun using more recent crop and weather data. Turnover processes underlying recommendations should be illustrated by flow diagrams of flux between pools, pie charts of fertilizer fate, bar charts of movement down the soil profile and graphical plots of changes in N status against time.     

Methylmercury in ambient air. Method of determination and some measurement results

When air containing CH₃HgY (Y stands for a monovalent anion) is bubbled through pure water (MQ), part of the airborne CH₃HgY, depending on the actual distribution constant (air/water), will be retained in the liquid phase. The resulting concentration, although usually very low, is now in many cases possible to determine, using the very sensitive analytical procedure developed by Bloom and Fitzgerald (1988). By means of an evaluation method, described in this paper, the concentration data, obtained in this way, can be used to give the average original concentration of CH₃HgY in the air which had entered the bubbler and its distribution constant (air/water) as well.     

Principal reactions of airborne mercury,ozone and some other microcomponent in pure water or very dilute sulfuric acid

Numerous bubblings of pure H₂O or very dilute H₂SO₄-solutions with ambient air have been undertaken. All of them have shown the formation of HgIIa and HgIIb in the liquid phase (nomenclature according to Brosset, 1987). With increasing air volume such systems clearly approach a steady state. Earlier it has been shown that Hg° in water is oxidized by O₃ primarily to Hg²⁺, (Brosset, l.c., Iverfeldt and Lindqvist, 1986, Munthe, Thesis 1991). However, the attainment of a steady state indicates that a reaction involving a removal of Hg from the solution must exist as well. It has now been anticipated that a substance ‘X’, present in the ambient air, should be responsible, at least partly, for this removal. Starting from this assumption a model has been developed, which seems to be supported by all experimental tests hitherto performed by us. Further it has been tried to establish the chemical nature of ‘X’. So far, some experiments show that ‘X’ may be (CH₃)₂S. Finally it has been shown that HgIIb observed in precipitation is not identical with the corresponding compound formed by bubbling of ambient air at the ground level through it.     

Mercury in precipitation and ambient air a new scenario

Theoretical calculations and experimental work, mainly consisting of bubbling ambient air through different synthetic solutions and natural waters and also bubbling Hg- and O₃-free air through precipitation samples, have given some new information. The oxidation process of Hg^o by means of O₃ in natural waters and in synthetic solutions has been clarified. The primary products are water soluble Hg-compounds which are reduced by SnCl₂. Subsequently volatile or nonvolatile Hg-species may be formed. These are not reduced by SnCl₂. Further it has been shown that in precipitation those Hg-forms, which are not reducible with SnCl₂ consist of non volatile species only. The dominant one seems to be highly dispersed and easily sorbed on to solid surfaces. It is reducible with NaBH₄. Besides this there is another one consisting of larger particles. Their core contains some Hg which can be released as Hg^o by a high temperature thermal process. Species with the same properties have also been observed in ambient air but in very low concentrations.     

Agricultural nitrogen balance and water quality in the UK

Abstract. Nutrient balance calculations have been advocated as indicators of the risk of nitrate loss from agricultural land. To explore this concept, a spatially distributed UK agricultural nitrogen balance was derived using annually updated statistics. The mean UK N surplus for 1995 was 115 kg N ha^–1, made up of 51 kg ha^–1for arable land, 140 kg ha^–1 for agricultural grassland (excluding rough grazing) and an additional 14 kg N ha^–1for agricultural land from pig and poultry units. Nitrogen surpluses were greater in lowland grassland (mainly in western, wetter areas) than in arable areas. However nitrate concentrations in rivers were generally greater in arable areas. The relationship between N balance and nitrate leaching was very different for grassland and arable systems, and was also sensitive to climate, level of inputs and management practices. Nitrogen surplus was therefore weakly or even negatively correlated with river nitrate concentrations or loads. A positive correlation was found only where the comparison was restricted to grassland-dominated catchments. Nitrogen surplus calculations identified areas of very high livestock densities, which would be associated with increased risk of pollution. However their use in isolation as indicators of N leaching, or of progress towards mitigation, could be misleading especially if comparing areas differing in land use, climate or soil type.     

OSTEOGENIC SARCOMA OF THE NASAL CAVITY IN A CAT: POSTOPERATIVE CONTROL WITH HIGH DOSE-PER-FRACTION RADIATION THERAPY AND METRONIDAZOLE

An 11-year-old Siamese cat with an osteogenic sarcoma of the nasal cavity was treated by partial surgical excision followed by a course of high dose-per-fraction radiation therapy in conjuction with metronidazole, a hypoxic cell sensitizer. Four thousand two hundred rads were delivered to the tumor in 7 weekly fractions. Each treatment was preceded by 6 gm/m² oral metronidazole given 3 hours before irradiation. There were no untoward side effects and the cat was in remission 2 years after treatment.     

Uptake of pesticides from water and soil by earthworms

The uptake of pesticides by earthworms from aqueous solutions was examined and shown to be a reversible physical process. Measurements of distributions of pesticides between aqueous solutions and worm solids showed that adsorption coefficients were related to octanol-water distribution coefficients, as are soil-water distributions. From these relationships it was calculated that concentration factors of stable chemicals in earthworms from soil should be similar, except for polar substances which penetrate poorly, and be determined mainly by the soil organic matter content. Examination of uptake from soils indicated that the calculated concentration factors are unlikely to be achieved because of slow diffusion of chemicals in soils and because of metabolism in the soil or the worm.     

Influence of compost amendments on the hydraulic functioning of brownfield soils

This study assessed the impact of compost on the hydraulic properties of three soils (sandy loam, clay loam and diesel‐contaminated sandy loam) with relatively poor physical quality typical of brownfield sites. Soils were amended with two composts at 750 t/ha. Samples were also collected from a clay‐capped brownfield site, previously amended with 250, 500 or 750 t/ha of compost. Water‐release characteristics and saturated hydraulic conductivity were determined for all soils and physical quality indicators derived. Unsaturated flow in field profiles after compost application with two depths of incorporation and two indigenous subsoils was simulated using Hydrus‐1D. Compost generally increased water retention. Hydraulic conductivity tended to decrease following compost application in sandy loam but increased in clay and clay loam, where compost addition resulted in a larger dominant pore size. Although compost improved physical quality indicators, they remained suboptimum in clay and clay loam soil, which exhibited poor aeration, and in the contaminated sandy loam, where available water capacity was limited, possibly due to changes in wettability. Increasing application rates in the field enhanced water retention at low potentials and hydraulic conductivity near saturation but did not alter physical quality indicators. Numerical simulation indicated that the 500 t/ha application resulted in the best soil moisture regime. Increasing the depth of incorporation in the clay cap improved drainage and reduced waterlogging, but incorporation in more permeable subsoil resulted in prolonged dry conditions to greater depths.