Effect of nitrogen inputs to cereals on nitrate leaching from sandy soils

Abstract. The effect of nitrogen fertilizer inputs to cereal crops on nitrate leaching after harvest was tested on 21 experiments on sandy soils in England. At small nitrogen fertilizer rates leaching increased very little with increasing inputs, while at high rates more than half of any additional nitrogen could be accounted for as increase in nitrate leached. In many cases the response fitted two straight lines. Nitrogen offtake in grain also fitted two straight lines, with a form which complemented the leaching response. The gradient averaged 0.52 kg N in grain for every additional 1kg N applied below the break point, but only 0.05 kg/kg above. The break points were generally close to or above the economic optimum N input. The effect of inputs on leaching could he quantitatively related to nitrogen offtake in grain, assuming a constant ratio of nitrogen in grain to total nitrogen uptake. The results show that fields receiving N inputs in excess of the economic optimum cause a disproportionately large nitrate loss. However because of uncertainty in predicting the break point in advance, modest further reduction in leaching will occur by reducing inputs to somewhat below the expected economic optimum.     

The transfer of methylmercury between ambient air and different lake waters

With the intention to elucidate, at least partly, why lakes situated nearby sometimes exhibit very different concentration of methylmercury in their fish population, two such lakes have been studied. A newly developed bubbling method was applied to determine very low concentrations of airborne methylmercury and the actual distribution constant (air/water). The water in one of the lakes studied was clear. In the other it was brownish. The result of the investigation showed that water in the clearwater lake with respect to the distribution of methylmercury between air and water behaved nearly in the same way as MQ-water. The behaviour of the brownish lakewater was however quite different. It turned out that the bubbling procedure in this case resulted in generation of some methylmercury in this water.     

Uptake and distribution of thiabendazole by seed potatoes

The uptake of thiabendazole into potato seed tubers (cultivar King Edward) was determined by the method of application, more being taken up from solutions and suspensions than from dusts. Penetration and uptake were greatest with solutions at pH 3, and less at higher or lower pHs. The addition of inorganic salts (KCl, CaCl₂) had no effect. Treatment of tubers with weak solutions of mineral acid increased uptake of thiabendazole. There was little movement and no metabolism of the chemical when potatoes were stored for 3 months.