Abstract

Pre-seeding tillage of long-term no-till soil may alter soil quality by changing some properties, but the magnitude of change depends on soil type and climatic conditions. Effects of short-term (2 or 3 years) tillage (hereafter called reverse tillage [RT]) of land previously under long-term no-till (NT, 29 or 30 years), with straw management (straw removed [S_Rem] and straw retained [S_Ret]) and N fertilizer rate (0, 50 and 100 kg N ha^-1 in S_Ret, and 0 kg N ha^-1 in S_Rem plots) were determined in autumn 2011 on total organic C (TOC) and N (TON), light fraction organic C (LFOC) and N (LFON), and mineralizable N (N_min) in the 0-7.5, 7.5-15, or 15-20 cm soil layers at Breton (Gray Luvisol [Typic Cryoboralf] loam) and Ellerslie (Black Chernozem [Albic Argicryoll] loam), Alberta, Canada. Short-term RT following long-term NT had no significant negative effect on TOC and TON in soil at both sites, although these parameters tended to be slightly lower in the 0-7.5 cm soil layer with RT compared to NT. For the zero-N treatment, S_Ret had greater TOC and TON compared to S_Rem in both soil layers at both sites. On average, over both sites, TOC and TON in the 0-15 cm soil increased by 2.08 Mg C ha^-1 and 0.216 Mg N ha^-1, respectively. Application of N fertilizer increased TOC and TON in both soil layers, up to the 50 kg N ha^-1 rate at Breton (by 7.96 Mg C ha^-1 and 0.702 Mg N ha^-1 in the 0-15 cm soil) and up to the 100 kg N ha^-1 rate at Ellerslie (by 5.11 Mg C ha^-1 and 0.439 Mg N ha^-1 in the 0-15 cm soil). In both RT and NT treatments, the effects of N rate on TOC and TON were similar for S_Ret and S_Rem. There was greater LFOC and LFON in the 7.5-15 cm soil layer with RT than NT at both sites. In the 0-15 cm soil layer, averaged over both sites, RT increased LFOC by 66 kg C ha^-1 and LFON by 4.0 kg N ha^-1. In both 0-7.5 and 7.5-15 cm soil layers, LFOC and LFON increased with S_Ret compared to S_Rem. Averaged over both sites, the increase in LFOC and LFON in the 0-15 cm soil was 97 kg C ha^-1 and 3.5 kg N ha^-1, respectively. Mass of LFOC and LFON increased dramatically in both soil layers with application of N fertilizer up to the 100 kg N ha^-1 rate at both sites, with an average increase of 866 kg C ha^-1 and 45.5 kg N ha^-1. In the zero-N treatment, LFOC and LFON increased with S_Ret compared to S_Rem under RT at Breton and under NT at Ellerslie. On average, tillage had no effect on N_min in soil, but S_Ret increased N_min in soil in both RT and NT, with an average increase of 4.8 kg N ha^-1. Application of N fertilizer increased N_min in the 0-20 cm soil up to 50 kg N ha^-1 rate at Breton (by 13.7 kg N ha^-1) and up to 100 kg N ha^-1 rate at Ellerslie (by 18.6 kg N ha^-1). In conclusion, RT had no effect on TOC, TON and N_min in soil, but LFOC and LFON increased with RT compared to NT in the 7.5-15 cm layer at one site. S_Ret and N fertilization usually had dramatic positive effects on TOC, TON, LFOC, LFON and N_min in soil compared to the corresponding treatments.

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