Agricultural management practices affect the dynamics of soil organic matter (SOM) by influencing the amount of plant residues returned to the soil and rate of residue and SOM decomposition. Total organic C and δ 13 C of soil were measured in two field experiments involving corn cropping to determine the effect of tillage practices on SOM dynamics. Minimum tillage (MT) and no tillage (NT) had no significant impact on the soil C compared with conventional tillage (CT) in the 0- to 50-cm soil depth sampled at both sites. Continuous corn under MT and CT for 29 yr in a silt loam soil sequestered 61–65 g m −2 yr −1 of corn-derived C (C 4 -C), and it accounted for 25–26% of the total C in the 0- to 50-cm depth. In a sandy loam soil cropped to corn for 6 yr, SOM contained 10 and 8.4% C 4 -C under CT and NT, respectively. Reduced tillage practices altered the distribution of C 4 -C in soil, causing the surface (0–5 cm) soil of reduced tillage (MT and NT) plots to have higher amounts of C 4 -C compared to CT. Tillage practices did not affect the turnover of C 3 -C in soil. Key words: Soil organic matter, 13 C natural abundance, tillage practices
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Agricultural management practices affect the dynamics of soil organic matter (SOM) by influencing the amount of plant residues returned to the soil and rate of residue and SOM decomposition. Total organic C and δ 13 C of soil were measured in two field experiments involving corn cropping to determine the effect of tillage practices on SOM dynamics. Minimum tillage (MT) and no tillage (NT) had no significant impact on the soil C compared with conventional tillage (CT) in the 0- to 50-cm soil depth sampled at both sites. Continuous corn under MT and CT for 29 yr in a silt loam soil sequestered 61–65 g m −2 yr −1 of corn-derived C (C 4 -C), and it accounted for 25–26% of the total C in the 0- to 50-cm depth. In a sandy loam soil cropped to corn for 6 yr, SOM contained 10 and 8.4% C 4 -C under CT and NT, respectively. Reduced tillage practices altered the distribution of C 4 -C in soil, causing the surface (0–5 cm) soil of reduced tillage (MT and NT) plots to have higher amounts of C 4 -C compared to CT. Tillage practices did not affect the turnover of C 3 -C in soil. Key words: Soil organic matter, 13 C natural abundance, tillage practices
Findings
What changed what, as the paper reports it. Grouped by the measured property. The largest groups are open; open the others as you need them.
no tillage (NT) vs. conventional tillage (CT)significant · 5–15 cm · fall1994 · Delhi
Numbers
treatment -25.65 vs. control -24.16 per mill (+6.167 %) · 5–10 cm
treatment -25.76 vs. control -24.59 per mill (+4.758 %) · 10–15 cm
Source · p. 3
“C values than those of corn under NT in the 5- to 15-cm soil layer.”
Source · p. 3
“The soil from corn under CT had significantly higher δ”
=no effect
no tillage (NT) vs. conventional tillage (CT)not significant · 20–50 cm · fall1994 · Delhi
Numbers
treatment -25.26 vs. control -25.07 per mill (+0.7579 %) · 20–25 cm
treatment -24.83 vs. control -24.35 per mill (+1.971 %) · 25–30 cm
treatment -24.84 vs. control -24.74 per mill (+0.4042 %) · 30–40 cm
treatment -25.35 vs. control -25.71 per mill (-1.4 %) · 40–50 cm
Source · p. 3
“The δ13C values of all three treatments were not significantly different in the 20- to 50-cm soil depth zone.”
=no effect
corn (CT and NT) vs. tobacco-rye (conventional tillage)not significant · 20–50 cm · fall1994 · Delhi · CT and NT variants each separately compared with tobacco-rye; every pair difference below its LSD; no pooled contrast.
Numbers
treatment -25.07 vs. control -25.8 per mill (-2.829 %) · 20–25 cm · CT
treatment -25.26 vs. control -25.8 per mill (-2.093 %) · 20–25 cm · NT
treatment -24.35 vs. control -25.77 per mill (-5.51 %) · 25–30 cm · CT
treatment -24.83 vs. control -25.77 per mill (-3.648 %) · 25–30 cm · NT
treatment -24.74 vs. control -26.25 per mill (-5.752 %) · 30–40 cm · CT
treatment -24.84 vs. control -26.25 per mill (-5.371 %) · 30–40 cm · NT
treatment -25.71 vs. control -26.27 per mill (-2.132 %) · 40–50 cm · CT
treatment -25.35 vs. control -26.27 per mill (-3.502 %) · 40–50 cm · NT
Source · p. 3
“The δ13C values of all three treatments were not significantly different in the 20- to 50-cm soil depth zone.”
=no effect
minimum tillage (MT) vs. conventional tillage (CT)not significant · 0–25 cm · spring1995 · Elora · Corn29yr; MTtillage15yr; forest excluded from pairLSD.
Numbers
treatment -21.85 vs. control -22.78 per mill (-4.083 %) · 0–5 cm
treatment -22.45 vs. control -22.71 per mill (-1.145 %) · 5–10 cm
treatment -23.06 vs. control -22.59 per mill (+2.081 %) · 10–15 cm
treatment -23.5 vs. control -22.62 per mill (+3.89 %) · 15–20 cm
treatment -24.1 vs. control -23.49 per mill (+2.597 %) · 20–25 cm
Source · p. 3
“Tillage practices at Elora had no”
Source · p. 3
“significant effect on the δ13C of soil, except in the 25- to 30cm soil depth zone”
↓decrease
minimum tillage (MT) vs. conventional tillage (CT)significant · 25–30 cm · spring1995 · Elora
Numbers
treatment -24.17 vs. control -23.55 per mill (+2.633 %)
minimum tillage (MT) vs. conventional tillage (CT)not significant · 30–50 cm · spring1995 · Elora
Numbers
treatment -24.4 vs. control -22.85 per mill (+6.783 %) · 30–40 cm
treatment -24.25 vs. control -24.3 per mill (-0.2058 %) · 40–50 cm
Source · p. 3
“Tillage practices at Elora had no”
Source · p. 3
“significant effect on the δ13C of soil, except in the 25- to 30cm soil depth zone”
proportion of corn-derived carbon (C4-C) in SOM
↓ 2= 46
=no effect
no tillage (NT) vs. conventional tillage (CT)not significant · 0–5 cm · fall 1994 · Delhi · Delhi surface fraction. Explicit nonsignificant NT/CT comparison, distinct from the significant 5-15 cm decrease. Figure 1 visually verified; percentages are printed in Results, not estimated from bars.
Numbers
treatment 21 vs. control 15 % (+40 %) · 0–5 cm
Source · p. 3
“No tillage at Delhi resulted in a higher proportion (21%) of C -C in SOM in the soil surface (0–5 cm) compared with4 CT (15%); however, this difference was not statistically significant (Fig. 1).”
corn-derived carbon (C4-C) stock in soil organic matter
↑ 1= 23
=no effect
Reduced tillage practices (MT and NT) vs. conventional tillage (CT)not significant · 0–50 cm · Delhi fall 1994; Elora spring 1995 · Delhi · Elora · Integrated 0-50 cm inventory. NT at Delhi after 6 years of corn; MT at Elora after 29 years of corn and 15 years of the tillage experiment. Practice variants merged; each site's pairwise LSD supports the null independently, without a pooled test. Layer-specific stock effects are not implied by this integrated inventory.
Numbers
treatment 185.2 vs. control 234.9 g m-2 soil (-21.16 %) · 0–50 cm · fall 1994 · Delhi NT versus CT; Table 7 Total row; columns verified in original PDF, LSD 93.4.
treatment 1,780 vs. control 1,888 g m-2 soil (-5.736 %) · 0–50 cm · spring 1995 · Elora MT versus CT; Table 8 Total row, LSD 602.7.
total organic carbon
= 11
=no effect
Reduced tillage practices (MT and NT) vs. conventional tillage (CT)not significant · 0–50 cm · Delhi fall1994;Elora spring1995 · Delhi · Elora · NTDelhi6yr versusCT; MTElora15yr tillage,29yr corn versusCT. Individual layers and cumulative profile all null by actual pairwiseLSD, not omnibus inference.
Numbers
treatment 465.5 vs. control 427.2 g m-2 soil (+8.965 %) · 0–5 cm · Delhi NT
treatment 381.6 vs. control 401.9 g m-2 soil (-5.051 %) · 5–10 cm · Delhi NT
treatment 378.4 vs. control 420.4 g m-2 soil (-9.99 %) · 10–15 cm · Delhi NT
treatment 353.8 vs. control 348.8 g m-2 soil (+1.433 %) · 15–20 cm · Delhi NT
treatment 225.8 vs. control 265.1 g m-2 soil (-14.82 %) · 20–25 cm · Delhi NT
Natural-abundance 13C partitioning using measured soil and corn-residue isotope signatures and a C3 reference; corn-derived fraction multiplied by measured soil C inventory.
no tillage (NT) vs. conventional tillage (CT)significant · 5–15 cm · fall 1994 · Delhi · Delhi. Named corn-derived fraction, an explicit study objective and abstract result; two consecutive significant layers merged. Figure 1 visually verified; no chart-derived means.
Source · p. 3
“Corn under CT had a significantly higher proportion of C4 -C in SOM compared with corn under NT in the 5- to 15-cm depth; the differences in the 15- to 50-cm depth were not significant.”
=no effect
no tillage (NT) vs. conventional tillage (CT)not significant · 15–50 cm · fall 1994 · Delhi · Delhi, five consecutive deeper fraction layers explicitly reported as nonsignificant. Separate from the significant 5-15 cm decrease. Figure 1 visually verified; no chart-derived means.
Source · p. 3
“Corn under CT had a significantly higher proportion of C4 -C in SOM compared with corn under NT in the 5- to 15-cm depth; the differences in the 15- to 50-cm depth were not significant.”
=no effect
minimum tillage (MT) vs. conventional tillage (CT)not significant · 0–25 cm · spring 1995 · Elora · Elora, 29 years of corn. Five consecutive upper fraction layers, with the surface explicitly nonsignificant and 25-30 cm identified as the sole significant layer. Figure 2 visually verified. Surface fraction null differs from the surface stock increase; printed surface percentages retained. Page 4 extraction interleaves columns, so separate verbatim passages support the two printed means.
Numbers
treatment 33 vs. control 26.5 % (+24.53 %) · 0–5 cm
Source · p. 4
“compared with MT (33%), and this difference was not sig- more C in the 0- to 5-cm layer, probably due to the effect of nificant (Fig. 2).”
Source · p. 4
“The proportion of C4 -C in SOM in corn residue retention on the soil surface and less incorporation under CT was only significantly higher than that of corn compared with CT. These results agree with previous studunder MT in the 25- to 30-cm soil depth zone.”
↓decrease
minimum tillage (MT) vs. conventional tillage (CT)significant · 25–30 cm · spring 1995 · Elora · Elora, 29 years of corn. Explicit sole significant fraction layer. Figure 2 visually verified; no chart-derived means. This is a source fraction, not the raw delta13C response or the surface stock.
Source · p. 4
“The proportion of C4 -C in SOM in corn residue retention on the soil surface and less incorporation under CT was only significantly higher than that of corn compared with CT. These results agree with previous studunder MT in the 25- to 30-cm soil depth zone.”
=no effect
minimum tillage (MT) vs. conventional tillage (CT)not significant · 30–50 cm · spring 1995 · Elora · Elora, 29 years of corn. Two consecutive deeper fraction layers; Results explicitly confines the significant fraction difference to 25-30 cm. Figure 2 visually verified; no chart-derived means. Separate deeper null run preserves the text-stated depth exception.
Source · p. 4
“The proportion of C4 -C in SOM in corn residue retention on the soil surface and less incorporation under CT was only significantly higher than that of corn compared with CT. These results agree with previous studunder MT in the 25- to 30-cm soil depth zone.”
Source · p. 7
“The total amount of corn-derived C in the 0- to 50-cm layer was not significantly affected by the tillage practices”
↑increase
minimum tillage (MT) vs. conventional tillage (CT)significant · 0–5 cm · spring 1995 · Elora · Elora, 29 years of corn. Table 8 pairwise LSD 103.3 at P=0.05. Abstract surface-stock statement verified against original table; Delhi NT surface stock is not included in this significant result (Table 7, 98.1 versus 62.4, LSD 43.3, P=0.079).
Numbers
treatment 438.7 vs. control 323.6 g m-2 soil (+35.57 %) · 0–5 cm
Source · p. 7
“It should be noted that the only significant difference observed in this study was in the 0- to 5-cm soil layer at Elora.”
Source · p. 6
“0–5 323.6 (33.8)
**x**
438.7 (47.2) 103.3 0.038”
=no effect
minimum tillage (MT) vs. conventional tillage (CT)not significant · 5–50 cm · spring 1995 · Elora · Elora, 29 years of corn. Seven consecutive deeper layers: each CT/MT difference is below its own Table 8 LSD at 0.05. Explicit Results and Discussion limit the stock difference to 0-5 cm; this is the complementary deeper null run, separate from the integrated profile.
Numbers
treatment 392 vs. control 333.3 g m-2 soil (+17.61 %) · 5–10 cm
treatment 352.2 vs. control 330.1 g m-2 soil (+6.695 %) · 10–15 cm
treatment 290.5 vs. control 361.3 g m-2 soil (-19.6 %) · 15–20 cm
treatment 86.7 vs. control 165.3 g m-2 soil (-47.55 %) · 20–25 cm
treatment 59.7 vs. control 77.6 g m-2 soil (-23.07 %) · 25–30 cm
treatment 76.9 vs. control 203.7 g m-2 soil (-62.25 %) · 30–40 cm
treatment 82.9 vs. control 92.6 g m-2 soil (-10.48 %) · 40–50 cm
Source · p. 7
“It should be noted that the only significant difference observed in this study was in the 0- to 5-cm soil layer at Elora.”
treatment 101.2 vs. control 163.8 g m-2 soil (-38.22 %) · 25–30 cm · Delhi NT
treatment 140.6 vs. control 166.8 g m-2 soil (-15.71 %) · 30–40 cm · Delhi NT
treatment 164.3 vs. control 143.3 g m-2 soil (+14.65 %) · 40–50 cm · Delhi NT
treatment 2,211 vs. control 2,338 g m-2 soil (-5.403 %) · 0–50 cm · Delhi NT,integrated profile
treatment 1,347 vs. control 1,224 g m-2 soil (+10.12 %) · 0–5 cm · Elora MT
treatment 1,385 vs. control 1,251 g m-2 soil (+10.72 %) · 5–10 cm · Elora MT
treatment 1,469 vs. control 1,245 g m-2 soil (+17.95 %) · 10–15 cm · Elora MT
treatment 1,368 vs. control 1,329 g m-2 soil (+2.904 %) · 15–20 cm · Elora MT
treatment 483.5 vs. control 705.1 g m-2 soil (-31.43 %) · 20–25 cm · Elora MT
treatment 307.9 vs. control 331.8 g m-2 soil (-7.203 %) · 25–30 cm · Elora MT
treatment 410.7 vs. control 694.9 g m-2 soil (-40.9 %) · 30–40 cm · Elora MT
treatment 395.6 vs. control 436.1 g m-2 soil (-9.287 %) · 40–50 cm · Elora MT
treatment 7,167 vs. control 7,217 g m-2 soil (-0.6942 %) · 0–50 cm · Elora MT,integrated profile
Source · p. 3
“Tillage method under corn did not affect the amount of organic C in the coarse-textured soil at Delhi”
Source · p. 3
“Results were similar at Elora where corn under CT or MT did not cause any significant changes in organic C of soil”
Source · p. 7
“Tillage practices had no significant impact on the soil C in any of the soil depths sampled at Delhi and Elora sites.”
