Effect of sampling date on nitrogen mobilization during incubation experiments
SummaryThe influence of time of sampling on nitrogen mobilisation in incubation experiments at 20°C with humus and mineral soil samples has been systematically investigated. After five and seven samplings, respectively, during the years 1967 and 1968, it has been established that the amounts of mineral nitrogen formed vary considerably more after incubation than other characteristics investigated in samples taken at different times.The variation is great in both humus layer and mineral soil (0–5 cm) and decreases somewhat when the incubation time increases from six to nine weeks.The dry weight, density, ignition loss and Kjeldahl nitrogen of the sample vary relatively little on different sampling occasions, usually with a variation coefficient by about five per cent.The mineral nitrogen after incubation showed rather large coefficients of variation (up to 57 per cent) for the years investigated.For this reason the time at which samples are collected for incubation experiments cannot be considered irrelevant.
The effect of nitrogenous fertilizers on the nitrification of forest soils
The effect of fertilization with urea and ammonium nitrate on nitrogen mineralization was studied in a series of laboratory incubation experiments. The samples (humus layer) were collected from field experiments with different applications of fertilizers during a period of 11–14 years. The nitrogen fertilization influenced some chemical properties of the humus layer such as pH, N-Kjeldahl content and the content of inorganic nitrogen, especially in the samples from North Sweden. Nitrate nitrogen was formed in humus samples classified as non-nitrifying in several cases, usually after urea fertilization.
Small-scale spatial variation in forest soil properties and its implications for sampling procedures
Soil samples from the various horizons have been collected from points in a square lattice in two areas representing typical Swedish forest types, at Garpenberg (60°27' lat.N, Dalarna) and Vindeln (64°17' lat. N, Vasterbotten). The samples were analysed for N, P, K and loss on ignition, and the values obtained were expressed both as percentages and per unit area. The conclusion to be drawn from the results is that to obtain good precision in analytical values, it is necessary to take a greater number of samples when the results are expressed in weight per unit area than when they are expressed in percentages by weight. As a rule, it is necessary to use samples from at least 10-15 points (often more)-aggregated to a composite sample-to depress the coefficient of variation below 10 per cent for the values per unit area of the studied elements. The paper also contains tables showing the distribution of these elements in the profiles examined.