Impact of Deep Ripping of Previous No-Tillage Cropland on Surface Soil Properties

The use of continuous no-tillage cropping raises concern about water and nutrient movement into subsoil due to high soil bulk density. Deep ripping (i.e., paraplowing) might be a conservation strategy to loosen surface and subsoil without excessive incorporation of surface crop residues. We initiated a multi-year study comprised of four water catchments (3.1-6.7 acres each) that had previously been under continuous no-tillage cropping for at least 10 years. Two of the water catchments were paraplowed each autumn, but managed otherwise with conservation tillage, similar to the two remaining water catchments. Soil-surface properties were evaluated during the first and second year of the study. Soil bulk density of the surface 20 cm was significantly lower under paraplowing (1.37 Mg · m) than under no tillage (1.51 Mg · m). Soil organic C was significantly greater under paraplowing (10.4 mg · g) than under no tillage (8.7 mg · g). Surface residue C was not different between tillage systems in either year. As the standing stock of total organic C in residue and soil to a depth of 20 cm, there was no difference between tillage systems in either year. We conclude from these early years of the study that annual paraplowing in combination with conservation tillage management had few negative impacts on soil-surface chemical properties and may have improved soil physical conditions to possibly allow greater water utilization. Introduction Crop management systems can vary greatly in their production potential and impacts on the environment. Tillage is an important management variable that influences long-term sustainability. Restoration of eroded cropland in the southeastern USA has been demonstrated with the development of conservation tillage systems, which limit soil disturbance and allow surface residue accumulation (Langdale et al., 1992). Long-term no-tillage management can increase infiltration by increasing soil macroporosity (Edwards et al., 1988). Many of the management options for achieving sustainability, however, are regionally specific, with variations due to soil type, climatic conditions, and landscape ecology. Land application of manure provides essential nutrients to crops and helps alleviate waste disposal. Poultry production in the Southern Piedmont is extensive (Census of Agriculture, 1992). Manure is often mixed with bedding material at the end of the production cycle, cleared from confinement housing, and applied as litter (manure plus bedding) to nearby land as a source of nutrients. Depending upon management, however, repeated application of poultry litter could become a source of excessive nutrients (Vervoot et al., 1999). Surface application of poultry manure without soil incorporation may potentially cause unwanted nutrient enrichment in surface water runoff, which can be high in the high-rainfall region of the southeastern USA. Of increasing concern is the unbalanced load of P in poultry manure compared with N. Crop production in the southeastern USA benefits greatly from P application, because these soils have a great capacity to fix P, especially in the subsurface clayey horizons. However, little information is available to predict the impact on surface water concentration of and soil profile distribution of P from poultry manure application to conservation tilled cropland. Increased density of soil under continuous no-tillage cropping could limit water and nutrient movement into subsoil. Deep ripping (i.e., paraplowing) might be a conservation strategy to loosen surface and subsoil without excessive incorporation of surface crop residues. This loosening of the soil could also enhance water and nutrient storage at lower depths than possible with continuous no tillage. We evaluated the effect of no tillage compared with paraplowing on surface-soil distribution of bulk density and organic C and N during the first two years of an intended long-term study. Surface water runoff volume and nutrient concentration will be reported in these proceedings by Endale et al. (2002). Other aspects of this study that will eventually be reported are agronomics, N cycling of broiler litter, soil-profile distribution of inorganic N and P, ammonia volatilization, water-use efficiency, and fecal-borne pathogen survival and transport. Materials and methods This study consisted of four small water catchments [3.1-6.7 acres each (1.3-2.7 ha)] located near Watkinsville, Georgia (33E 52' N, 83E 25' W). Soils are Cecil sandy loam (fine, kaolinitic, thermic Typic Kanhapludult). These soils are classified as well drained with moderate permeability. Mean annual precipitation is 49" (1250 mm) and temperature is 62 EF (16.5 EC). The four water catchments were managed separately under various forms of cropping and forage production since 1972. Two water catchments (P1 and P2) were separated by 0.5 mile. The other two water catchments (P3 and P4) were immediately adjacent to each other and separated from P1 by 2.3 miles and from P2 by 1.8 miles. Prior to this experiment, all water catchments were managed with no tillage for at least 10 years. In autumn 1998, the four water catchments were managed together. Two water catchments (P1 and P3) were allowed to continue under continuous no tillage and the other two water catchments (P2 and P4) were converted to no tillage planting of all crops with autumn paraplowing following harvest of the summer crop. Paraplowing depth was ca. 12-16" (30-40 cm). Summer crops were maize (Zea mays) in 1999, pearl millet (Pennisetum glaucum) In 2000, and grain sorghum (Sorghum bicolor) in 2001. Winter crops were crimson clover (Trifolium incarnatum) on P2 and P3 and rye (Secale cereale) on P1 and P4 in 1998/1999, barley (Hordeum vulgare) in 1999/2000, and rye in 2000/2001. Crops were fertilized according to soil test with inorganic N-P-K, as well as with broiler litter in July 2000, July 2001, and December 2001 at 1.1 ton · acre (2.48±0.25 Mg · ha · application). Soils were collected from each water catchment in five zones, which served as pseudoreplicates for analyses. The five zones represented the waterway and four corners of each water catchment. Within each zone, eight sites separated by -50' (15 m) were sampled and composited. At each site, surface residue was collected from 64 sq. in. (20 x 20 cm) areas by first removing green plant material above -1.5"-height (4 cm) and then collecting all surface residue to ground level by cutting with a battery-powered hand shears. Following surface residue removal, a soil core [1.6" diam (4.1-cm diam)] was sectioned into depths of 0-1.2, 1.22.4, 2.4-4.7, and 4.7-7.9" (0-3, 3-6, 6-12, and 12-20 cm). Surface residue was dried at 158 E F (70 EC) for several days, ground to <1/32" (1 mm), and analyzed for total C and N with dry combustion. Soil was dried at 131 EF (55 EC) for 3 days, initially passed through a sieve with openings of 3/16" (4.75 mm) to remove stones, a subsample ground in a ball mill for 5 minutes, and analyzed for total C and N with dry combustion. Soil bulk density was calculated from the total dry weight of soil and volume of coring device. Standing stock values of soil organic C and total soil N to a depth of 7.9" (0-20-cm depth) were calculated based on the density and volume of each soil depth section. Stratification ratios of soil properties were calculated based on the weighted concentration of a soil property at a depth of 0-6 cm divided by the concentration of that property at a depth of 12-20 cm. Data were analyzed for variance due to tillage system within each depth using the general linear models procedure of SAS (SAS Institute Inc., 1990). Differences among tillage systems were considered significant at P#0.1. Results and discussion Soil bulk density was significantly lower under paraplowing (PP) than under no tillage (NT) at all soil depths to 20 cm in February 1999 (Table 1). Soil samples from February 1999 were collected ca. 4 months following the first paraplowing operation in this experiment. The vertical breaking action of the paraplow tool had a strong loosening effect on soil density. Except for no difference between tillage systems at a depth of 0-3 cm, soil bulk density in February 2000 responded similarly to tillage management as during the sampling in February 2000. Although paraplowing reduced soil bulk density, compaction of soil under NT was not excessive. Soil bulk density >1.7 Mg · m might be expected to hinder root growth of many plants. The protective layer of surface residue and accumulation of surface soil organic matter were very likely important long-term attributes that helped to alleviate excessive surface-soil compaction with continuous NT. Soil organic C and total soil N concentrations were greater under PP than under NT at depths of 3-6 and 6-12 cm during sampling in 1999 and 2000 (Table 1). Some surface residue incorporation with paraplowing likely contributed to this tillage effect. Soil organic C and total soil N at a depth of 0-3 cm were also greater under PP than under NT in 1999, but not significantly different between tillage systems in 2000. Perhaps the more frequently that paraplowing is employed, the more disturbed the plow layer will become, which could eventually result in a decline in soil organic matter pools. This temporal effect will be evaluated in years to come. Taken to a depth of 0-20 cm, soil organic C and total soil N were significantly greater under PP than under NT in February 1999 (Table 1). This analysis on a gravimetric basis was counteracted by the significantly lower soil bulk density with PP than with NT resulting in no significant difference in the stock of soil organic C and total soil N on a volumetric basis between tillage systems in either 1999 or 2000 (Table 2). Surface residue C, although numerically lower under PP than under NT in both years, was not significantly different between tillage systems in either 1999 or 2000 (Table 2). However, surface residue N was significantly lower under PP than under NT in 1999, but not different in 2000. Surface residue C averaged 12 ± 1% of the total standing stock of C to a depth of 20 cm. Surface residue N averaged 6 ± 2% of the total standing stock of N to a depth of 20 cm. Surface residue C and N in either of these conservation tillage management systems were a significant portion of the total C and N of the near surface budget. This differs considerably with conventional tillage systems, in which surface residue C and N are often <1% (Franzluebbers et al., 1999). The C:N ratio of soil organic matter increased gradually with depth in both tillage management systems during both years (Table 1). The C:N ratio of soil organic matter at a depth of 0-3 cm was significantly greater under PP than under NT in 1999 and 2000. Differences in C:N ratio of soil organic matter between tillage systems were often not significant at lower depths. The C:N ratio of surface residue was 25 ± 7 among tillage systems and sampling dates. This ratio is similar to that reported for 13 crop and pasture management systems from the same geographic region on similar soils (27 ± 8) (Franzluebbers et al., 2000). Stratification of soil bulk density during the sampling in February 1999 was the only property measured with a significant difference between tillage systems (Table 3). The lower stratification ratio under PP than under NT suggested that total soil porosity (i.e., the inverse of bulk density) was improved more under PP than under NT. Stratification ratios of soil organic C and total soil N were 3.7 ± 0.4 among tillage systems and sampling dates. These ratios are intermediately high on a theoretical scale that has been proposed to assess soil ecosystem functioning (Franzluebbers, 2002). The fact that paraplowing did not reduce the stratification ratio of soil organic C and total soil N suggests that this operation may not be detrimental to soil quality or ecosystem functioning. The energy requirements of paraplowing are not minor. Yet the benefit of paraplowing on increasing total soil porosity without destroying surface soil organic matter should be considered as a possible option to improve soil water-plant relations and possibly reduce water runoff concentration of nutrients. ConclusionsThis early evaluation of annual deep ripping (i.e., paraplowing) with conservation tillagecompared with continuous no-tillage cropping suggests that soil physical conditions could beimproved with deep ripping and that surface residue and soil organic C and total soil N could bemaintained without significant degradation. We intend to evaluate these treatments in thisexperimental setup for at least five years. ReferencesCensus of Agriculture. 1992. Geographic area series 1B: U.S. summary and county level data.U.S. Dept. Commerce, Economics, and Statistics Admin., Bureau of the Census.Edwards, W.M., M.J. Shipitalo, and L.D. Norton. 1988. Contribution of macroporosity toinfiltration in a continuous corn no-tilled watershed: Implications for contaminantmovement. J. Contam. Hydrol. 3:193-205. Endale, D.M., H.H. Schomberg, A.J. Franzluebbers, R.R. Sharpe, and M.B. Jenkins. 2002.Impact of deep ripping of previously no-tillage cropland on runoff and water quality. (Theseproceedings).Franzluebbers, A.J. 2002. Soil organic matter stratification ratio as an indicator of soil quality. Soil Till. Res. (in press).Franzluebbers, A.J., G.W. Langdale, and H.H. Schomberg. 1999. Soil carbon, nitrogen, andaggregation in response to type and frequency of tillage. Soil Sci. Soc. Am. J. 63:349-355. Franzluebbers, A.J., J.A. Stuedemann, H.H. Schomberg, and S.R. Wilkinson. 2000. Soil organicC and N pools under long-term pasture management in the Southern Piedmont USA. SoilBiol. Biochem. 32:469-478.Langdale, G.W., L.T. West, R.R. Bruce, W.P. Miller, and A.W. Thomas. 1992. Restoration oferoded soil with conservation tillage. Soil Technol. 5:81-90. Vervoot, R.W., D.E. Radcliffe, M.L. Cabrera, and M. Latimore, Jr. 1999. Field scale nitrogenand phosphorus losses from hay fields receiving fresh and composted broiler litter. J.Environ. Qual. 27:1246-1254. Table 1. Surface-soil properties as affected by tillage system during the first and second year.Paraplowing was in November 1998 and 1999. Soil depthFeb 1999 Tillage system Feb 2000 Inchescm NTPPNT PP Soil bulk density (Mg · m)0-1.2 0-31.18 *** 0.981.031.011.2-2.4 3-61.46 *** 1.271.44 *** 1.262.4-4.7 6-121.63 *** 1.461.58 *** 1.424.7-7.9 12-201.61 ** 1.501.61 *** 1.49 0-7.9 0-201.53 *** 1.381.49 *** 1.36 Soil organic C (mg ·g)0-1.2 0-321.6 ** 26.924.723.31.2-2.4 3-611.3 ** 14.913.1 * 16.52.4-4.7 6-126.6 * 8.77.6 * 9.44.7-7.9 12-204.8 † 6.15.36.2 0-7.9 0-208.2 * 10.39.2 † 10.5 Total soil N (mg · g)0-1.2 0-32.33 * 2.692.722.381.2-2.4 3-61.21 ** 1.521.37 † 1.642.4-4.7 6-120.64 * 0.810.73 * 0.884.7-7.9 12-200.430.500.490.53 0-7.9 0-200.82 * 0.970.921.00 C:N ratio of soil organic matter (g · g)0-1.2 0-39.5 ** 10.29.3 * 10.11.2-2.4 3-69.6 † 9.99.910.22.4-4.7 6-1210.510.810.710.74.7-7.9 12-2011.212.511.011.8 0-7.9 0-2010.1 † 10.710.110.6 †, *, **, and *** indicate significant differences between tillage systems within a year at P#0.01,P#0.05, P#0.01, and P#0.001, respectively.NT is continuous no tillage and PP is conservation tillage with autumn paraplowing. Table 2. Surface residue and soil organic C and N stocks as affected by tillage system during thefirst and second year. Paraplowing was in November 1998 and 1999. Feb 1999 Tillage system Feb 2000 ComponentNTPPNTPP C stocks (g · m)Surface residue382337377336Soil (0-6 cm)1228 * 13401319 1323Soil (6-20 cm)1259148513961521 Soil (0-20 cm)2487282527152844Total (residue + soil) 2869316230923180 N stocks (g ·m)Surface residue23 * 151113Soil (0-6 cm)131135141 133Soil (6-20 cm)118131131138 Soil (0-20 cm)249266272271Total (residue + soil) 271281283284 * indicates significant difference between tillage systems within a year at P#0.05. Table 3. Stratification ratio (0-6 cm / 12-20 cm) of soil properties as affected by tillage systemduring the first and second year. Paraplowing was in November 1998 and 1999. Feb 1999 Tillage system Feb 2000 Soil propertyNTPPNTPP Soil bulk density (Mg · m) 0.82 * 0.750.770.76Soil organic C (mg · g) 3.33.43.43.3Total soil N (mg · g) 3.94.23.93.9C:N (mg · g)0.90.80.90.9 * indicates significant difference between tillage systems within a year at P#0.05.