No abstract

Grassland soils in Northern China are being seriously degraded under cultivation and grazing. This study investigated the impacts of land use on soil erosion and soil fertility in alpine grassland of China. Land uses included three levels of pasture degradation, lightly (LDP), moderately (MDP), and heavily degraded pasture (HDP) classified based on vegetation cover, and cultivated fields ranging from 1 to 50 yr of cultivation. Soil samples were collected from 18 sites at seven locations in Chernozemic soils between elevations of 2600 to 3000 m. Soil erosion was estimated by 137Cs radioactivity. When pasture was heavily degraded, 137Cs activity was significantly reduced, and organic C (OC), total N, and cation‐exchange capacity declined by 33, 28, and 18% respectively. Cultivation of grassland worsened soil erosion, and after 8‐, 16‐, and 41‐yr cultivation soil OC decreased by 25, 39, and 55%, respectively. Regionally, 59% of OC was lost within 30 to 50 yr of cultivation. There were concomitant losses of total N and exchange capacity. On cultivated soils, soil erosion and mineralization were equally responsible for organic C losses. Pasture degradation and cultivation also caused changes in soil P. Mineralization of organic P, incorporation of subsoil by tillage following erosion, and fertilization increased levels of Ca‐P in cultivated fields. This study indicated that grassland degradation and cultivation caused not only severe soil erosion, but also fertility decline and chemical changes of P dynamics.

Field studies were conducted for 3 yr at two locations in Manitoba, Canada, to evaluate the effect of various sources and rates of Se fertilizer on crop growth and the Se and Cd concentrations of durum wheat. Selenium concentration in durum wheat grown without Se application ranged from 195 to 532 µg kg-1 over the 6 site-years. Selenium seed coating, “Selcote” commercial granular fertilizer, and a foliar spray of sodium selenate solution applied at Feekes stage 5 all increased Se concentration in durum wheat grain at all locations, without negative effects on crop stand, biomass yield or grain yield. Regardless of treatment, Cd concentration in the grain was generally below proposed regulatory limits. Application of Se did not reduce Cd concentration in the grain, regardless of Se source. Selenium fertilization can be used to increase Se concentration of durum wheat, but is not an effective means of reducing the grain Cd concentration. Key words: Selcote, sodium selenate, seed-coating, selenium, cadmium

study of controlled release urea and split applications of nitrogen as compared with non-coated urea under conventional and reduced tillage management. Can. J. Plant Sci. 93: 523Á534. To evaluate the use of controlled-release urea (CRU) as a beneficial management practice for nitrogen management of wheat, barley, and canola, a multi-location study was conducted from 2004 to 2006 in a range of agro-environments across western Canada. The objective was to evaluate the relative economic performance of CRU and non-coated urea (NCU) for their effects on seed yield and quality, costs and net revenue (NR) using conventional tillage (CT) and reduced tillage (RT) management under varying environmental conditions. The NR was estimated as the income remaining after paying for all cash costs, ownership costs on machinery and buildings, and labour. The main factor affecting crop yield and NR was N application rate. In general, application of NCU produced similar or higher net revenues than that of CRU, split fertilizer applications or a blend of NCU and CRU. There were some limited situations where the use of split applications, CRU or CRU in a blend with the NCU increased crop yield as compared with NCU; however, the increased yield was not sufficient to cover the extra costs of CRU or the split application. The impact of tillage system on crop yield and NR was not consistent. Net revenue was higher under CT than RT for certain crops in some regions, but not in all regions or for all crops. Overall, NR analysis indicated that use of CRU did not provide an economic benefit over the use of NCU.

In spite of the management practices adopted by Canadian producers to mimize fertilizer losses, N‐use efficiency is normally estimated to be less than 50% in the year of application. Various types of enhanced‐efficiency fertilizers such as nitrification inhibitors, urease inhibitors, and coated N fertilizers are available that attempt to address the constraints associated with traditional N management in order to improve N‐use efficiency and/or the operational efficiency of Canadian agricultural systems. Enhanced‐efficiency N fertilizers can chemically or physically influence the movement and transformations of N in order to improve synchrony between nutrient supply and crop uptake, reduce nutrient losses, and improve nutrient‐use efficiency. Pathways and magnitude of N loss are influenced by soil characteristics, weather conditions, and crop management practices, as well as by fertilizer source and management practices. Therefore, the effectiveness of the various enhanced‐efficiency fertilizers will be strongly dependent on the environmental conditions that influence potential losses. Under environmental conditions where the potential for N loss is high, enhanced‐efficiency fertilizers may provide an effective method of improving N use, particularly where other agronomic factors are optimized so that the crop is able to convert the N supplied into usable yield with the greatest efficiency.