Abstract
<p>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<sub>Rem</sub>] and straw retained [S<sub>Ret</sub>]) and N fertilizer rate (0, 50 and 100 kg N ha<sup>-1 </sup>in S<sub>Ret</sub>, and 0 kg N ha<sup>-1 </sup>in S<sub>Rem</sub> 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<sub>min</sub>) 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<sub>Ret</sub> had greater TOC and TON compared to S<sub>Rem</sub> 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<sup>-1</sup> and 0.216 Mg N ha<sup>-1</sup>, respectively. Application of N fertilizer increased TOC and TON in both soil layers, up to the 50 kg N ha<sup>-1</sup> rate at Breton (by 7.96 Mg C ha<sup>-1</sup> and 0.702 Mg N ha<sup>-1</sup> in the 0-15 cm soil) and up to the 100 kg N ha<sup>-1</sup> rate at Ellerslie (by 5.11 Mg C ha<sup>-1</sup> and 0.439 Mg N ha<sup>-1</sup> 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<sub>Ret</sub> and S<sub>Rem. </sub>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<sup>-1</sup> and LFON by 4.0 kg N ha<sup>-1</sup>. In both 0-7.5 and 7.5-15 cm soil layers, LFOC and LFON increased with S<sub>Ret</sub> compared to S<sub>Rem.</sub> Averaged over both sites, the increase in LFOC and LFON in the 0-15 cm soil was 97 kg C ha<sup>-1</sup> and 3.5 kg N ha<sup>-1</sup>, respectively. Mass of LFOC and LFON increased dramatically in both soil layers with application of N fertilizer up to the 100 kg N ha<sup>-1</sup> rate at both sites, with an average increase of 866 kg C ha<sup>-1</sup> and 45.5 kg N ha<sup>-1</sup>. In the zero-N treatment, LFOC and LFON increased with S<sub>Ret</sub> compared to S<sub>Rem</sub> under RT at Breton and under NT at Ellerslie. On average, tillage had no effect on N<sub>min</sub> in soil, but S<sub>Ret</sub> increased N<sub>min </sub>in soil in both RT and NT, with an average increase of 4.8 kg N ha<sup>-1</sup>. Application of N fertilizer increased N<sub>min</sub> in the 0-20 cm soil up to 50 kg N ha<sup>-1</sup> rate at Breton (by 13.7 kg N ha<sup>-1</sup>) and up to 100 kg N ha<sup>-1</sup> rate at Ellerslie (by 18.6 kg N ha<sup>-1</sup>). In conclusion, RT had no effect on TOC, TON and N<sub>min</sub> in soil, but LFOC and LFON increased with RT compared to NT in the 7.5-15 cm layer at one site. S<sub>Ret</sub> and N fertilization usually had dramatic positive effects on TOC, TON, LFOC, LFON and N<sub>min</sub> in soil compared to the corresponding treatments.</p>
Highlights
In the Prairie Provinces of Canada, farmers traditionally used tillage for seedbed preparation to facilitate seeding operations, seed germination and weed control
Short-term RT following long-term NT had no significant negative effect on total organic C (TOC) and TON in soil at both sites, these parameters tended to be slightly lower in the 0-7.5 cm soil layer with RT compared to NT
One would expect a decrease of total organic C in soil under RT compared to NT, especially in soils with relatively low initial organic matter content
Summary
In the Prairie Provinces of Canada, farmers traditionally used tillage for seedbed preparation to facilitate seeding operations, seed germination and weed control. Tillage is expected to expose some of the protected soil organic C (SOC) by breaking the aggregates through physical action and making it more accessible to soil microorganisms for faster decomposition This information is needed, since there is very limited research on the effects of tillage of previously long-term NT soil on crop yield and nutrient uptake, soil fertility, and persistence of organic C in soil that was gained/stored under NT on individual farm fields (Lal et al, 1990; Campbell et al, 1988, 1996, 1998; Hassink, 1997; Yang & Kay, 2001a; Six et al, 2002b; Vandenbygaart & Kay, 2004; Baan et al, 2009), especially in the Parkland region of western Canada where large quantities of crop residue are produced and left on land after harvest. This paper discusses the effects of RT on soil quality parameters, related to quantity and quality of soil organic C and N
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