Mineralization of nitrogen in long-term pasture soils: effects of management

Abstract

A field incubation technique with acetylene to inhibit nitrification was used to estimate net N mineralization rates in some grassland soils through an annual cycle. Measurements were made on previously long-term grazed pastures on a silty clay loam soil in S.W. England which had background managements of +/-drainage and +/-fertilizer (200 kg N ha-1 yr-1). The effect of fertilizer addition on mineralization during the year of measurement was also determined. Small plots with animals excluded, and with herbage clipped and removed were used as treatment areas and measurements were made using an incubation period of 7 days at intervals of 7 or 14 days through the year. Soil temperature, moisture and mineral N contents were also determined. Mineralization rates fluctuated considerably in each treatment. Maximum daily rates ranged from 1.01 to 3.19 kg N ha-~, and there was substantial net release of N through the winter period (representing, on average, 27% of the annual release). Changes in temperature accounted for 35% of the variability but there was little significant effect of soil moisture. Annual net release of N ranged from 135 kg ha-1 (undrained soil, no previous or current fertilizer) to 376 (drained soil, + 200 kg N ha-1 yr-1 previous and current fertilizer addition). Addition of fertilizer N to a previously unfertilized sward significantly increased the net release of N but there was no immediate effect of withholding fertilizer on mineralization during the year in which measurements were made.

Resilience of soil microbial activity and of amino acid dynamics to the removal of plant carbon inputs during winter

“…In conclusion, low temperature simulated overwintering of soil caused a gradual decline in the concentration of dissolved organic solutes in soil solution. Even at temperatures reflecting the coldest months for the soil it was apparent that the microbial community was still very active and that lowering the temperature did not inhibit the processing of organic N. This supports previous studies demonstrating significant nitrification in winter in a range of ecosystems (Vance & David, 1991;Jackson et al, 1994;Gill et al, 1995). Our results also suggest that despite continual microbial activity over a four month period, significant reserves of DOC, DON and amino acids remained in soil.…”

Nitrogen management in organic farming: comparison of crop rotation residual effects on yields, N leaching and soil conditions

“…Franko (1984) and Gill et al (1995) confirm that mineralization can provide quite substantial N at low temperatures. During two weeks in mid January daily temperatures were on average 8.5°C (5.6-13.2°C) and rainfall amounted to 100 mm of which 45 mm occurred within 3 days.…”

Slurry 15NH4-N recovery in herbage and soil: effects of application method and timing

“…Since only a small proportion of the recovered soil N was in the form of inorganic N, and the rate of mineralisation is relatively low in the cold and wet winter months (Gill et al 1995), we hypothesize that benefits from residual effects (implication 2) may outweigh increased losses (implication 1).…”