Anderson, D.W.

Cowell, L.E.

English

eCommons@USASK

The effect of crop rotation history on nitrogen and sulphur mineralization in Luvisolic soils

University of Saskatchewan Research Archive

THE EFFECT OF CROP ROTATION HISTORY ON NITROGEN AND SULPHUR MINERALIZATION IN LUVISOLIC SOILS L.E. Cowell and D.W. Anderson Department of Soil Science, University of Saskatchewan Saskatoon, Saskatchewan Over 90% of nitrogen (N) and sulphur (S) compounds in soil are organic and are released as available nutrients by mineralization. Mineralization is a microbial process and is, therefore, affected by everything that modifies the soil environment. Cultivation of virgin land will alter the biological and physico-chemical environment of the soil. Luvisolic soils change markedly when converted from native conditions to cul ti vat ion in that surface leafy 1 itter is mixed into the soil. Many projects have studied the effect of cultivation on the total carbon, nitrogen and sulphur levels in the soil. Less is known of the effect of cul ti vat ion on mineralizable N and s. The objectives of this research were: i) To study the effect of a wide variety of crop rotations, including virgin forest, on the mineralization of Nand Sin Luvisolic soils, and ii) To study the relationships among mineralizable N and S, and total organic C, N, Sand HI~reducible sulphur (HI~s). HI-S refers to ester-bonded sulphur (C-O-S) as opposed to carbon-bonded sulphur (C-S). HI-S is considered more labile. Two locations were seleeted in the Luvisolic (Grey) soil zone of Saskatchewan. Both locations were mapped as Wai tville loam. The first location was south of Star City (Township 44, Range 17, W2) and the second 300 location was north of Hafford (Oscar Lake - Township 46, Range 10, W3). These locations will be referred to as SC and OL, respectively. Both locations are in well-established farming districts. Reasonably accurate histories were obtained for each site, in an effort to produce results which would reflect the farming practices used on the land (Table 1). Each location included a comparable virgin site with native aspen vegetation. Table 1 provides descriptive histories of each site. Samples were taken in the summer of 1984. A volumetric probe (15 em deep) removed the Ap horizon of the cultivated sites, and the approximate depth to which cultivation would mix the soil at virgin sites. Small roots were included but top growth was removed. Three cores were obtained, dried and weighed for bulk density calculation, then mixed and subsampled for analysis of organic C, and total N, Sand HI-S (Table 2). Three replicates of each site were placed in incubation units at 28°C for the mineralization experiment. Each soil was leached with 0.001 M CaCl 2 and a nutrient solution lacking either N or S. The leachates were analyzed for mineralized N and S with a Dionex exchange column. This procedure was repeated on days 7, 21, 35, 54, 70 and 84; a total of 12 weeks were therefore involved. The data were expressed as kg/ha, with a hectare volume being one hectare in area and 15 em deep. RESULTS Initial C, N and S Interrelationships There was as much organic C and slightly more N and S in the long-term cultivated soils as compared to virgin and short-term cultivated soils. This is in contrast to grassland soils, which generally have less organic matter 301 Table 1. Descriptive histories of sites. Site Cropping (vegetative) history Designation SC01 SC02 SC03 SC04 SC05 SC06 SC07 SC08 OL01 OL02 OL03 OL04 OL05 OL06 OL07 Virgin aspen forest. Pasture; cleared of forest about 1900 Cultivated in wheat~fallow rotation with occasional clover since 1900; presently in fallow. Originally sampled as a 30-year continuous fallow; however, sample apparently was contaminated by discarded grain and retained only for.experimental comparison. Recently cleared by chain-saw; most surface litter incorporated into soil. Cleared of bush between 1900 and 1910, with alfalfa from 1973 to 1983. Flax was present (1984) crop. Comparable to SC07 and SC08. Virgin aspen forest. Similar to SC06, but without alfalfa crop. Sampled after a wheat crop. Cleared of bush about 1925, farmed in crop-fallow rotation with a sweet clover forage crop every 5 years. Presently in fallow. As OL01, about 10 meters away. Virgin aspen forest. Similar to OL01, but with a alfalfa-grass forage mix for the past 4 years. Cultivated since 1964 as OL01. Virgin aspen forest. Recently cleared with a blade, with most surface litter removed. Key: Virgin (V); Pasture (P); Long-term cultivation (LT); Short-term cultivation (ST); Medium-term cultivation (MT); History unknown (?) 302 v p LT ? ST LT v LT LT LT v LT MT v ST Table 2. Average amount of organic nitrogen, sulphur and carbon in the upper 15 em of soil water various rotations Bulk Organic Organic Organic Organic Crop density c N s HI-S C/N/S rotation (g/ em 3 ) (kg/ha) (kg/ha) (kg/ha) (kg/ha) ratio Virgint 0. 91 4.88x10" 3220 277 78 186/11.7/1 Long-term 1. 31 4.60x10" 4033 380 1 33.7 121/9.32/1 cul ti vat ion'¥ Short-term 1. 11 4.56x10" 3163 302 91 1 66/1 0. 5/1 cul ti vationa: Pastures 1. 09 5.35x10" 3368 322 93 1 66/1 o. 5/1 tAverage of SC01, SC07, OL03, and OL06 '¥Average of SC03, SC06, SC08, OL01, OL02, OL04 and OL05 a:Average of SC05 and OL07 sSC02 only when cul ti vat ed. Higher total and HI-S in long-term cultivated sites, despite crop removal, may be due to additions of S fertilizer, but probably results from a more efficient storage of S in soil organa-mineral complexes. In addition, there was a significant increase in the percentage of s as HI-S, from 27.6+5.2 in the virgin sites to 35.4.::_3.3 in the long-term cultivated sites. Crop rotation was a significant factor affecting organic C, N and s (Table 2). Organic C was more strongly correlated with organic N than organic S, since one-third of the organic S was as HI-S, and not directly bonded to C. Organic Nand S were strongly correlated in the total soil (Table 3). This indicates a constant form and amount of N and S in Luvisolic soils which cultivation did not affect. 303 Table 3. Comparison of r values of selected relationships on total organic matter of all sites, and of virgin and long-term cultivation sites. Relationship Organic C vs. Organic N Organic C vs. OrganicS Organic N vs. OrganicS OrganicS vs. Organic HI-S All sites 0.716** 0.620** 0.965*** 0.960*** Virgin ( 4 sites) 0.957** 0.464 0. 858* 0.994*** Long-term cultivation ( 7 sites) t 0.934*** 0.936*** 0.961*** 0. 982*** tLong-term sites include SC03, SC06, SC08, OL01, OL02, OL05 and OL06 *Significant at P .05 **Significant at P .01 ***Significant at P .001 Mineralization Characteristics Over the 84 days, N and S mineralization was highly correlated with time (Table 4; Figure 1). Site SC07 was representative of native sites that showed marked initial depressions in N mineralization. No discernible depressions were seen in S mineralization. Significance of past rotation practices was established with t-tests (Tables 5 and 6). A comparison oft-tests shows significant differences inN mineralization among soils from long-term cultivated sites, probably related to recent cropping. Largest differences were between short-term cultivated and long-term cultivated sites. The long-term pasture site (SC02) was significant from all others, being closest to SC06, the soil broken from alfalfa. With S mineralization, the greatest differences were between long-term cultivated soils and virgin or short•term cultivates sites, indicating a change in organic S with cultivation. Differences among cultivation treat-304 Table 4. Analyses of cumulative nitrogen and sulphur released with time. Cumulative N Cumulative s mineralized r 2 of mineralized r 2 of Site + crn-1 N mineralized + crn-1 S mineralized (kg/ha) VS. time (kg/ha) vs 0 time SC01 ( V) 1 84. 3 + 1 5. 6 0.988 'i 3. 5 + 1 • 3 0.998 SC02 ( P) 221 . 5 + 1 3. 1 0.998 1 5' 5 + 1 . 7 0.990 SC03 ( LT) 1 97. 8 + 9.7 0.982 22.6 + 0. 96 0. 964 SC04 ( ?) 179. 8 + 6.0 0.996 13.6 + 1 • 1 0.998 SC05 ( ST) 98.3 + 42.9 0.996 9.04 + 2.9 0.998 SC06 ( LT-A) 263.8 + 17.4 0.994 1 6. 7 + 0' 15 0.998 SCOT ( V) 144.4 + 8.6 0.922 1 1 • 7 + 0. 45 0.998 SC08 ( LT) 1 75. 8 + 1 6. 7 0.998 1 4. 1 + 1 • 4 0.998 OL01 ( LT) 285.4 + 8.9 0.995 1 7. 9 + 0. 98 1 . 000 OL02 ( LT) 277.4 + 21 . 5 0.998 20.5+1,0 0.998 OL03 ( V) 242.5 + 1 8. 4 0.994 14.5 + 0.99 0.996 OL04 ( LT-F) 263.8 + 1 4. 1 0.998 18.3 + 0.99 0.994 -OL05 (MT) 306.0 + 38.9 0.994 35.4 + 0.27 0.998 OL06 ( V) 178.3 + 48.9 0.992 1 2. 9 + 1 '3 0.988 OL07 ( ST) 234.2 + 5.8 0.996 1 5. 8 + 0. 53 0.998 Key: Virgin (V); Pasture (P); Long-term cultivation (LT); Short-term cultivation (ST); Medium-term cultivation (MT); Long-term cultivation with recent alfalfa (LT-A); Long-term culitivation now under forage (LT-F); History unknown ( ?) 305 Figure 1. Mineralization curves for nitrogen and sulphur. 350 • 16 300 • • OL02 NitroQen 14 0 0 SC02 NltroQen ~ ..c: ....... ::J 250 A SC07 NitroQen (I) 0' 12 ~ ~ OL01 Sulphur Q - • N' c: 0 scoe Sulphur (I) Q) ~ 0' 200 10 w e en 0 c: 0\ +-z "'0 ::r 9 c: ~ "'0 150 Q) -N "' 8 cO 0 ....... ~ ::r Q) c: Q :!: -4 2 Weeks of Incubation Table 5. t-tests for nitrogen mineralization. Star City Nitrogen SC01 SC02 SC03 SC04 SC05 SC06 SC07 SC08 SC01 6.83 2.75 1, 01 1 8. 06 6.52 6.39 1. 39 SC02 5.44 1 0. 83 29.42 3.53 1 3 0 24 8.06 SC03 5.90 28.72 5. 61 1 0. 03 4.26 SC04 29.08 7.26 7.20 0.84 SC05 1 4. 1 5 8.89 1 5. 4 4 SC06 9. 65 7. 15 SC07 4.87 Oscar Lake Nitrogen OL01 OL02 OL03 OL04 OL05 OL06 OL07 OL01 1.29 7.85 4.85 1. 93 8.06 1 8. 03 OL02 4. 61 1. 98 2. 41 6.94 7.26 OL03 3.44 5.52 4.60 1. 61 OL04 3.82 6.29 7.26 OL05 7.65 6.83 OL06 4.26 OL07 d p 0. 001 ; t 3.674 t n 28 p o. 01 ; t 2.763 s-d p 0.05; t 2.048 307 Table 6. t-tests for sulphur mineralization. Star City Sulphur SC01 SC02 SC03 SC04 SC05 SC06 SC07 SC08 SC01 3.51 18.82 0.22 12.05 3.84 5. 06 1.20 SC02 11 • 80 3.52 1 3. 76 1. 38 1 3. 76 8. 31 SC03 20.58 44.32 6. 06 38.1 2 1 6. 24 SC04 1 4. 26 3. 81 6.30 1.07 SC05 9.87 20.98 12.52 SC06 6. 51 3.04 SC07 6. 1 8 Oscar Lake Sulphur OL01 OL02 OL03 OL04 OL05 OL06 OL07 OL01 6. 81 9.08 o. 61 7 64.34 11.29 6.88 OL02 1 5. 58 3. 17 51.82 1 6. 81 1 4. 91 OL03 5.58 76.06 3. 68 4.43 OL04 26.98 7.52 3.84 OL05 61.5 9 1 22. 85 OL06 7. 71 OL07 d p = 0. 001 ; t = 3. 674 t = -- n = 28 p = 0.01; t = 2.763 s-d p = 0.05; t = 2.048 308 ments were significant as well. The pasture (SC02) differed from all sites except the alfalfa breaking, consistent with observations for N minerali-zation. At Oscar Lake, the OL05 site differed markedly from all others in S mineralization. This site had the greatest amount of HI-S, but otherwise was not different from the other sites. Factors Influencing Mineralizable N and S Total mineralizable N and S were strongly correlated. If sites SC03 and SC05 are not included, an r value of 0.941 results. The N/S ratios of the total soil (x = 10.7) were lower than the mineralized ratios (x = 13.5) in all but two sites. There appears to be a small pool of organic compounds which is most important to mineralization, and this pool had a wider N/S ratio than the total organic matter. Correlation coefficients of several relationships of mineralized N and S were calculated (Table 7). Crop rotation had a definite effect on several relationships. The relationship between HI-S and mineralized S remained significant, indicating the importance of this fraction in supplying plant available S. Effect of Specific Crop Rotations on Mineralization Virgin sites. Virgin sites showed initial lags inN mineralization. This may reflect the high C/N ratios of virgin sites, an initial lag in microbial activity, or a possible enzymatic inhibition by tannins and related compounds from the leaf litter. No lag was shown inS mineralization, though the virgin sites did have lower S mineralization rates. It must be remembered that the virgin soil was not in a natural state, as it was mixed before incubation. Thus, the mineralization rates cannot be transposed to the native environment. 309 Table 7. Comparison of r values of selected relationships of mineralized nitrogen and sulphur in all sites, and virgin and long-term cultivation sites. Relationship All sites Mineralized N vs. Total c 0. 251 Mineralized s VS. Total c 0.078 Mineralized N vs. Total N 0.642** Mineralized s vs. Total s 0.559* Mineralized N vs. C/N -0.713** Mineralized s vs. CIS -0.571* Mineralized s vs. Total HI-S 0.663** tLong-term sites include SC03, SC06, SC08, *r value significant at p 0.05 **r value significant at p 0. 01 Virgin ( 4 sites) 0.632 -0.642 0. 738 0.785 ~o. 736 -0.796 0. 81 6* OL01, OL02, Long-term cultivation (7 sites )t 0.554 -0.246 0.606 0.512 0. 122 -0.146 0.788* OL05 and OL06 Short-term cultivation sites. Both SC05 and OL07 showed low N and S mineralization rates. SC05, in particular, released little inorganic Nor S. The incorporation of relatively more leaf litter into SC05, cleared with a chain-saw, than OL07 (cleared with a bull-dozer) may explain the lowre net mineralization of S at SC05. Long-term pasture site. SC02 showed increased total C, N and s. In addition, bulk density was not significantly increased from the virgin SC01 site. Nand S mineralization was also relatively high. Permanent pasture definitely improved the quality of the soil. Long-term cultivation sites. Long-term cul ti vat ion generally increased bulk density, reduced organic C levels, but increased organic N, S and HI-S levels (Table 2). The highest mineralization rates were observed in 310 long-term cultivation sites. Site SC06 showed the effect of a long-tel~m alfalfa crop. Though total N and S were not increased, more N and S were mineralized. Alfalfa built up the pool of mineralizable Ot~ganic compounds, though organic matter levels were not increased. SC08, adjacent to SC06, did not have the recent alfalfa crop and had lower mineralization rates. SC08 also had lowS mineralization, despite a large HI-S pool. This suggests there is a subfraction of HI-S most respon-sible for mineralization and that this fraction I¥ as depleted by crop growth. OL sites showed similar results. mineralization in all sites. Physical Properties of the Soil Cultivation increased N and S Cultivation also affects physical properties of the soiL This is reflected by the increased bulk density in cultivated sites (Table 1). Adverse soil structure was evident when the soils were leached during the incubation procedure. Cultivated soils became more difficult to leach with time. Structural problems are likely a greater limitation in Luvisolic soils than fertility problems. It is interesting to note that many of the Luvisolic soils with an apparent soil structure problem have as much as 2. 5% Ot~ganic carbon (4% organic matter), an amount adequate for good structure in Chernozemt c ar·eas, In this respect, forage rotations and limited fallow would improve the soil. CONCLUSIONS Crop rotation proved to be a significant factor in determining total organic C, N, Sand HI-S. N/S ratios of both the soil and the mineralized fraction ~-1as not affected by cultivation. There was a significantly higher 311 proportion of HI-S in cultivated soils than in forest or short-term culti-vated soils. HI--S and miner ali zed S were strongly correlated. A long-term pasture site maintained total organic matter and increased mineralization rates. Long-term cultivation sites showed gains in total N and S despite slight losses of' organic C. This resulted in increased mineralization rates in long-term cultivation sites. Thus, quality of organic matter increased despite a slight decrease in quantity. Soil bulk density was higher in the long-term cultivated sites, a consequence of lower organic matter (carbon) concentrations. Legumes increased mineralization rates, apparently by increasing the mineralizable pool of organic matter. Legumes should be considered in field management by the farmer. Crop rotation history is definitely a significant factor which must be accounted for in studying the mineralization of N or S, and in assessing the long-term effects of different management practices. 312 

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The effect of crop rotation history on nitrogen and sulphur mineralization in Luvisolic soils

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