Impact of human activity on NO soil fluxes

Changes in land use driven by the increasing demand of food are affecting the fluxes of trace gases to the atmosphere. The more important human activities that affect NO soil fluxes are: deforestation, intensification of agricultural practices, and biomass burning. In this review emphasis is given to identifying the physicochemical and biological processes involved in the changes, and no attempt to quantify their contribution to global or regional NO budgets is made.Conversion of tropical forest to pasture is occurring very rapidly. An increase of the NO emission is observed immediately after deforestation (1–5 years) followed by a significant decrease (below forest levels) in old pastures and secondary successional forests. It seems that deforested tropical areas produce, in the long term, less NO than primary forests. The observed changes are not completely understood, but are most likely driven by the availability of exchangeable nitrogen and the bacteria' population.Soil plowing and fertilization are important factors that affect NO fluxes in agricultural soils. Plowing increases soil porosity and aeration, as well increasing the surface area that is exposed to the atmosphere. These physical changes increase the production of soil nitrate, and the escape efficiency of NO from the soil, enhancing NO fluxes. The emission of NO from fertilized soils depends on many variables: type of fertilizer (i.e. ammonium, nitrate), the structure of the soil microbial community (e.g., populations of nitrifiers and denitrifiers), meteorogical conditions (e.g. soil moisture and temperature), and soil management (e.g. plowing). A combination of these factors should explain the large range reported for the fraction of N-fertilizer that is emitted as NO to the atmosphere. Measurements made in diverse ecosystems show that vegetation burning enhances NO soil emissions. However, it seems that different processes, which are not well understood, occur at the various sites; e.g., in the tropical savannah, enhanced emissions, from dry soils, are observed immediately after burning, whereas in Californian chaparral burned dry soils emit on average less than the unburned plots, and the fluxes only increase after soil wetting. Changes in the physical conditions of the soil surface and N availability are the most likely factors that explain the increased fluxes.     

Changes in glycoalkaloids content of potatoes destined for consumption

The purpose of the present study was to determine glycoalkaloid content of early potato cultivars, grown with the use of various N rates and subsequent changes resulting from preparation of potatoes for consumption. The material taken for the study consisted of three very early potato cultivars from the growing seasons of 2003–2005: Bard, Lord and Denar, grown in the experimental plots belonging to Wroclaw University of Environmental and Life Sciences.     

Protein Quality and Energy Density of Leek (Allium porrum L) as Influenced by Water and Nitrogen Supply and Plant Age at Harvest

Leeks were cultivated under conditions differing in level of nitrogen (N) supply (100 kg N ha^-1, 160 kg N ha^-1, 220 kg N ha^-1, 280 kg N ha^-1), level of water supply (normal, low) and time of harvest (September, October, November). Based on chemical analysis and balance studies on rats the nutritive value of the 26 batches of leek was determined. The protein content of the leeks increased progressively from 90 g kg^-1 DM to 163 g kg^-1 DM with N-supply. This increase in protein was associated with a reduction of all essential amino acids (g per 16 g N) and, subsequently, a reduction of the biological value. Protein and energy digestibilities increased with level of N-supply. Leeks harvested in September had a higher protein content, but had at the same time the lowest biological value as compared to leeks harvested in October or November. This was due to a lower content of essential amino acids (g per 16 g N) in leeks harvested in September as compared to leeks of later harvest. Only small differences between the two levels of water supply were observed in the chemical composition of the leeks. The content of non-starch polysaccharides (NSP) was rather high in all samples of leek (approximately 240–280 g kg^-1 DM) and appeared to be unaffected by the growth conditions applied in the investigation. Soluble-NSP constituted approximately half of the total NSP. © 1997 SCI.     

Nitrogen balances in long-term field experiments

The influence of fertilization with different N doses on nitrate-N content of the deeper soil layers were investigated in soils of long-term experiments at the experimental stations of the National Fertilizer Experimental Network in Hungary. Distribution of nitrate-N with depth was also studied in plots fertilized with different N doses. Although these experiments were set up according to an identical experimental plan at every location, after 20 years of experimentation substantial differences could be detected in the nitrate-N contents, nitrate-N distribution profiles on plots of the same treatments, as well as in the yield and the nitrogen uptake of the cultivated plants at the various sites. These differences are attributed to differences in soil properties and in environmental conditions existing at the individual experimental stations. The conclusions drawn from the data are very important when evaluating the role of nitrogen fertilization in the nitrate-contamination of soils, surface water and groundwater, and for a more precise determination of the N doses to be applied under specific soil and environmental conditions.     

Nitrogen response of fluted pumpkin (Telfairia occidentalis Hook. F) grown sole or intercropped with banana

In the 1994 and 1995 cropping seasons, fluted pumpkin(Telfairia occidentalis Hook. F) was intercropped withbanana (Musa AAA) or grown alone. The flutedpumpkin, whether intercropped or grown alone, received 30 to 120 kgNha^–1 in the first cropping season and 80 to320kg N ha^–1 in the following season. Fluted pumpkinplants grown alone or which did not receive N served as controls. The objectiveof the study was to determine the N requirement of fluted pumpkin when grownalone or as an intercrop. Intercropping significantly decreased vine yield andnumber of fruits set in the 1994 cropping season, but it did not significantlyinfluence number of fruits set in the 1995 cropping season. In both croppingseasons, intercropping had no significant effect on fruit yield. In the 1994cropping season, linear trends were significant for the response of vine yieldto N fertilization. In the 1995 cropping season, quadratic trends weresignificant for the response of fruit set and fruit yield to N fertilization.There was no interaction between cropping systems and N fertilization. Based oncash advantage due to fertilizer application values, 160 kg Nha^–1 was considered optimal for dual purpose (vegetable+ seed) production of fluted pumpkin.