Summary Simulation models of net mineralization of nitrogen (N) in soil need to be able to incorporate the effect of soil water. Our objective was to identify and define the best way of expressing soil water and its effect on net mineralization across a range of soil types. We collated data from 12 laboratory incubation studies, including a total of 33 different soils, where rates of net mineralization of N were determined from the net accumulation of mineral N under a range of water contents at near‐optimal temperatures. Measurements of water potential and limits of water content observed in the field were available for most of these soils. The percentage of pore space filled with water was estimated from measurements of soil bulk density. We found that relative water content, particularly when expressed relative to an upper and lower limit of water content observed in the field, was the best descriptor for net mineralization. The next best descriptions were soil water potential, water content relative to the optimal water content for mineralization, and percentage of pore space filled with water, with water content alone being poor. Although various functions may be used to describe the relation between relative water content and net mineralization of N, an equation for a sigmoidal curve provided the best fit, and explained 78% of the variation.

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The effects of slash and litter management practices on soil water and temperature, fluxes of mineral N, needle water potential, and tree nutrition and growth were studied in a young Pinusradiata D. Don plantation growing on a sandy Podzol in southeastern Australia. Treatments were slash and litter retained (SL), litter only retained (L), litter ploughed (LP), and slash and litter removed (SLR). Soils without slash or litter cover (LP and SLR) were up to 4 °C warmer on average than soils overlaid by slash or litter and were subjected to greater extremes of temperature. Treatments had relatively little effect on soil water content and needle water potential in trees. Carbon in surface soil increased from 1.14 to 1.83% after incorporation of litter by ploughing, but decreased to 1.37% during the next 40 months. Smaller but significant decreases in C also occurred in other treatments. LP and SLR led to the highest rates of N mineralization in the 1st year. During the first 3 years after clear-felling, rates of N mineralization increased in SL, L, and LP but decreased in SLR. During the 4th year, rates of N mineralization were low (20–30 kg N•ha−1•year−1) in all treatments. Over 4 years, 211, 170, 210, and 147 kg N•ha−1 were mineralized in treatments SL, L, LP, and SLR, respectively. Rates of mineralization and leaching were strongly correlated (R2 = 0.82) and leaching below 30 cm accounted for 75–85% of N mineralized irrespective of treatment. Incorporation of litter by ploughing doubled concentrations of mineral N during the first summer after planting and increased early tree growth. However, rates of N mineralization in the slash and litter treatments, which were high compared with potential rates of uptake, were weakly correlated with tree growth. Factors controlling N supply were of little consequence for tree growth during this early phase of plantation establishment.

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The effects of clear-felling and slash removal on the distribution of organic matter and nutrients, fluxes of mineral N, and soil water and temperature were studied in a 37-year-old Pinusradiata D. Don plantation, on a sandy Podzol in southeastern Australia. Slash, litter, and the top 30 cm of soil combined contained 1957 kg N•ha−1, of which slash and litter contained 12 and 25%, respectively. Therefore, loss of slash and litter due to burning or other intensive site preparation practices would substantially reduce the N capital at the site. During the first 18 months after clear-felling, soil water content in the clear-felled area was up to 50% higher than in the uncut plantation, but there were only minor differences in soil temperature. Slash removal decreased the water content of litter, but had little effect on the water content or temperature of the soil. In the uncut plantation, N mineralized in litter and soil was completely taken up by the trees. Following clear-felling, rates of N mineralization increased in litter after 4 months, and in soil after 12 months, but changes were less pronounced with slash removal. After clear-felling, increased mineralization and the absence of trees (no uptake) led to increased concentrations of mineral N in both litter and soil, 64–76% of which was leached below the 30 cm soil depth prior to replanting. Despite leaching, concentrations of mineral N after clear-felling remained higher than those in the uncut plantation for at least 3 years.