Nitrogen dynamics during till and no-till pasture restoration sequences in Rondônia, Brazil

Abstract

The clearing of tropical rain forest in the Amazon basin has created large areas of cattle pasture that are now declining in productivity. Practices adopted by ranchers to restore productivity to degraded pastures have the potential to alter soil N availability and gaseous N losses from soils. We examined how soil inorganic N pools, net N mineralization and net nitrification rates, nitrification potential and NO and N 2 O emissions from soils of a degraded pasture responded to the following restoration treatments: (1) soil tillage followed by replanting of grass and fertilization, (2) no-till application of non-selective herbicide, planting of rice, harvest followed by no-till replanting of grass and fertilization, and (3) the same no-till sequence with soybeans instead of rice. Tillage increased soil NH 4 + and NO 3 À pools but NH 4 + and NO 3 À pools remained relatively constant in the control and no-till treatments. Cumulative rates of net N mineralization and net nitrification during the first 6 months after treatment varied widely but were hightest in the tilled treatment. Emissions of NO and N 2 O fluxes increased with tillage and with N fertilization. There were no clear relationships among rates of N fertilizer application, net N mineralization, net nitrification, NO, N 2 O and total N oxide emissions. Our results indicate that pasture restoration sequences involving tilling and fertilizing will increase emissions of N oxides, but the magnitude of the increase is likely to differ based on timing of fertilizer application relative to the presence of plants and the magnitude of plant N demand. Emissions of N oxides appear to be decreased by the use of restoration sequences that minimize reductions in pasture grass cover.

Ploughing a poorly drained grassland reduced N2O emissions compared to chemical fallow

“…In studies of well-drained, semi-arid soils of Brazil (Do Carmo et al, 2005) and in cool humid soils in Great Britain and the Netherlands (Davies et al, 2001;Velthof et al, 2010) peak emissions typically occurred for 10-15 d after grassland ploughing. Emissions following ploughing of managed grasslands range from 1 to 5 mg N 2 O m À2 h À1 , though they are typically higher when fertilizer N is applied at the same time as ploughing (Davies et al, 2001;Dobbie and Smith, 2003;Ball et al, 2007;Mori and Hojito, 2007).…”

Synthesis, characterization and application of hydrogel derived from cellulose acetate as a substrate for slow-release NPK fertilizer and water retention in soil

“…While 14 reducing fertilizer application can compromise crop productivity, 15 reducing nutrient losses in fertilizer application by using 16 substrates that perform controlled-release or slow-release while 17 conserving soil moisture is considered a promising alternative 18 [1,2]. 19 According to Carmo et al [3] and Nogueira et al [4] the overuse 20 of mineral fertilizers, mainly fertilizers with nitrogen (ammonium 21 and nitrate), can cause environmental impacts. The mineral 22 fertilizers are inefficient; therefore, it is necessary to apply several 23 times, especially when it comes to highly mobile nutrients such as 24 N and K. Thus, they may be leached into rivers and lakes to cause 25 eutrophication.…”

Short-term changes in nitrogen availability, gas fluxes (CO2, NO, N2O) and microbial biomass after tillage during pasture re-establishment in Rondônia, Brazil

“…Peak NO 3 À following tillage was 6 times higher than in the control, ranging from 0.24 to 6.3 kg N ha À1 . Tillage increased rates of net N mineralization compared with the control for 10 days, after which net immobilization dominated over net mineralization but did not lead to a clear change in net nitrification rates (Carmo et al, 2005b).…”