Quality of a silty clay soil after 22 years in plow, chisel and no-till was compared to grass. Plowing degraded soil at a faster rate than chisel, while no-till enhanced quality. Plowing reduced total N of grass by 5300 lb/ac, while N was only reduced 2600 lb/ac with no-till. Plow lowered organic C in grass soil by 11,000 lb/ac, while no-till sequestered 10,600 lb/ac. Carbon dioxide evolution from soil was 0.70 g/cm3 for plow, and carbon dioxide evolution from grass with chisel or no-till was at 0.50 g/cm3. Soil pH, EC, Ca, Na, Fe, and Cu were higher in plow than chisel or no-till. No-till enhanced soil physical and biological properties that eliminated Fe and Zn deficiency in grain legumes present on plow. Erodible soil aggregates (< 2 mm) were highest on plow and chisel that, combined with low surface residue cover, subjected these systems to wind erosion potential.
Soil quality has gained attention in recent years due to environmental issues related to soil degradation. Soil quality has also gained the attention of producers interested in the sustainability of their soils or farming systems. The term soil quality is often open to interpretation, but has been defined as the capacity of a soil to function within ecosystem boundaries to sustain biological productivity, maintain environmental quality, and promote plant and animal health (Doran & Parkin, 1994). A discussion of the links between soil quality and the health of plants, animals, and humans is provided by Cihacek et al. (1996). The quality or health of a soil can be determined by monitoring, over time, specific chemical, physical, or biological properties. Once the properties are measured, the producer can infer quality values and make changes in management if the quality is deteriorating.
Janzen, et al. (1992) suggested that soil quality must be expressed in terms of productivity. Productivity is determined by land management, which can influence the chemical, physical, and biological properties of the soil. The climate, topography, and hydrology at any specific location also modify quality of the soil. Deibert (1997) summarizes these intrinsic and extrinsic factors in relation to conservation tillage. Carbon sequestration by soils has gained attention with the adoption of the international Kyoto Protocol on reduction of greenhouse gas as summarized by Bruce, et al. (1999) and McConkey, et al. (1999). Soils can serve as sinks to remove carbon dioxide from the air and a better understanding of these processes or relationships is needed. A meeting at Ohio State University presented an overview of current knowledge and research gaps (Lal, et al., 1996). Participants at the meeting indicated that additional information is needed in 10 specific areas, including the magnitude of inorganic carbon in arid regions, carbon sequestration with soil depth under different management practices, the interaction of N, P, and S with carbon sequestration, and the relationships of soil quality or soil structure to enhance the capacity of the soil to serve as a carbon sink. An international symposium on agricultural practices and policies for carbon sequestration in soil was recently held at Ohio State University (1999). Cihacek and Ulmer (1995) presented some preliminary work on soil organic carbon losses in a long-term crop-fallow system on the Great Plains. They indicated that carbon loss from tillage incorporated crop residue was a greater contributor to atmospheric C losses than was due to prior cultivation when prorated over 80 years. Little information was available on the relationship of carbon and other long-term residue management-crop rotations found in the Northern Plains. Recently Follet and McConkey (2000) made some estimates of the amount of carbon that can be sequestered in the Great Plains by using good agricultural practices. Halvorson, et al. (2000), discussed the effect of nitrogen fertilization on carbon sequestration.
The objectives of this study were: (1) to measure selected chemical, physical, and biological properties on a grassland area and on three long-term 22-year residue management systems in a small grain-row crop rotation to determine the impact on soil quality; (2) to determine carbon sequestration in the soil profile under the different systems; and (3) to measure the evolution of carbon dioxide from the soil with the different systems under different N fertilizer variables over two different crop seasons.
Changes in soil quality over short periods of time are usually quite subtle; thus, longer periods are needed to evaluate measurable changes in soil properties due to various management practices. The research site used in this study is one of a few locations in the northern Great Plains of the United States where management practices have continued for more than 20 years, offering the opportunity to measure changes in soil quality on a cultivated site compared to an adjacent grassland area. The chemical, physical, and biological properties measured in this study will provide some baseline information on the impact of long-term residue management and crop rotation practices on soil quality in the northern Great Plains. This information can also be used to develop best management practices to maintain the sustainability of soils, one of our most precious resources. This information can be used as a guide for selecting soil properties that producers can use to best evaluate the quality of their soil in relation to productivity. Results will also provide additional data for the Soil Quality Institute within the Natural Resource Conservation Service (NRCS), which is currently focusing on soil quality guidelines as part of their conservation effort. The soil carbon and carbon dioxide respiration information under different management practices will fill the void in data needed (outlined at recent meetings on carbon sequestration at Ohio State University in 1996 and 1999) to understand the relationships and develop models for determining the soil as a sink for carbon sequestration under arid and semi-arid climatic conditions present in the Northern Plains.
A research site was selected in eastern North Dakota that has been maintained for the last 22 years in a replicated small grain (spring wheat, barley, and durum) row crop (sugarbeet, sunflower, soybean, dry edible bean, and field pea) rotation under three different cultivated residue management systems (0% to 10%, 30% to 50%, and 70% to 90% surface residue cover that comprise a plow, chisel and no-till system). Nitrogen rate (0, 40, 80, 120 lb N/ac every other year) variables have been previously established during the long-term trial. The cultivated site was planted to durum (Triticum turgidum L.) in 2000 and field pea (Pisum sativum L.) in 2001 using recommended practices for seeding and weed control. Adjacent to the cultivated site is a grass area that has not been cultivated or fertilized in more than 30 years. Grass species on the area included 85% blue grass (Poa pratensis), 10% bromegrass (Bromus inermis) and 5% quack grass (Agropyron repens). This grass area was used for comparison of changes in various soil quality parameters and carbon flux with the cultivated site.
Replicated intact 4-foot soil profile cores were collected in plastic sleeves inside metal tubes with a hydraulic operated probe truck. Cores from the different cultivated residue management-fertilizer variable plots and grassland area were sampled in the fall of 2000 or spring of 2001. Individual soil profile cores were taken to the lab and separated into 0-3, 3-6, 6-12, 12-18, 18-24, 24-30, 30-36, 36-42 and 42-48 inch increments. The physical property of bulk density was determined on each increment using recommended methods (Klute, 1986). Soil from each increment was air dried, bagged, labeled, ground to pass a 1 mm sieve and a portion sent to the NDSU Soil Testing Lab to determine chemical properties (organic matter, extractable P, exchangeable K, pH, EC, exchangeable secondary elements including Ca, Mg, Na, and extractable micronutrients like Zn, Fe, Mn, Cu) using standard procedures (Brown, 1998; Leeman Labs; Tamulynas).
Bulk soil samples were collected in the spring from both cultivated and grass areas to measure the physical property aggregation. Replicated samples were collected from the surface profile (0-2 inch), placed in large flat containers, returned to the lab, air dried, placed in plastic containers and later subsamples used to measure aggregate size distribution (dry rotary sieve) using standard methods (Klute, 1986). The physical property water infiltration was determined in the spring or fall on both the grass area and cultivated sites using a single ring procedure (Sarrantonio, et al., 1996). An 8-inch diameter by 6-inch deep metal core was pounded 3 inches into the soil at two random sites in each replication of the grass and cultivated sites. An amount of water equal to one inch (780 mls) was applied initially (dry) and timed. A second one inch of water was applied (wet) and timed. Infiltration was calculated based on the amount of time required for the water to move into the soil.
Three biological properties (earthworm activity, microbial populations, and plant root mycorrhizae colonization) were evaluated with additional soil samples collected in 2001. Multiple soil samples were collected in the grass and cultivated areas by pounding a metal core (8-inch diameter by 6-inch deep) into the soil when earthworms are active and extracting the sample. Each soil sample was hand sorted and washed to determine cocoon, juvenile, and adult earthworm populations as outlined in a procedure developed by the principal investigators in this proposal (Deibert et al., 1991). Soil cores (1-inch diameter by 6-inch deep) were collected in plastic sleeves with a hand probe from the cultivated areas during the growing season. These small cores were returned to the lab with soil plated to determine bacteria and fungal populations using recognized techniques (Weaver, et al., 1994; Alef & Nannipieri, 1995). Soil cores were collected during the growing season from the field pea crops with the roots extracted to determine the presence of mycorrhizae as outlined by Norris, et al. (1994).
Subsamples from the profile soil core samples in Objective 1 were finely ground with a ball mill and analyzed for carbon and nitrogen. Carbon (total, inorganic and organic) was determined with a SKALAR PRIMACS Solid Carbon analyzer (Skalar, 1997), which uses an EPA method (EPA, 1995). Total N was determined using standard procedures (Page, 1982). Whole plant samples were collected each year at maturity from the grass site and durum (1st year) and field pea (2nd year) to determine total dry matter produced and the portion added to the soil system as residue. Total N and C of the residue material were also determined using standard procedures (Chapman & Pratt, 1961; Miller & Kotuby-Amacher, 1996) to measure their contribution to the system.
Respiration of carbon dioxide was measured on both the grass area and cultivated sites at selected time periods during the growing season (May-September) using a portable infrared gas analyzer (PP Systems, 1993). Random replicated measurement sites in both the cultivated sites under different N management and grass area were marked to insure measurement of respiration at the same location each sample time throughout the growing season. A round 8-inch diameter core was inserted into the soil after planting. The gas analyzer chamber was inserted in a specially designed plastic cover, which was placed over the core at sample time.
Replicated soil and plant data were evaluated using various statistical procedures to determine the long term effect of residue management, crop rotation and nitrogen fertilizer on the chemical, physical, and biological soil quality variables to compare the three cultivated residue management systems sites with the grassland area.
Although determining plant growth was not an integral part of the objectives for this study, the information on total production, grain removal, and residue returned to the soil are helpful in understanding any changes associated with the physical, chemical, and biological properties in the soil. Dry matter values usually varied with climatic conditions and crops produced, but the values presented are typical of production for the soil and area. Dry matter production on the grass, depending on year, ranged from 1750 to 2480 lbs/acre. Grass dry matter was cut by mowing and returned to the soil surface for decomposition and incorporation by biological activity. The total dry produced under the small grain (durum in 2000) averaged 7,300 lbs/acre with differences among residue management systems. Over the years, the no-till has produced higher values, while during wet years the plow produced higher dry matter (Deibert & Utter, 2002; Deibert, 1997; Deibert, 1995: Deibert & Utter, 1990; Deibert, 1989a: Deibert, 1989b). During normal years, all systems performed equally. The average grain dry matter removed from the system was 2,180 lbs/acre with around 5,120 lbs/acre residue returned to the soil. These values are probably typical of the production from the small grain/grain legume over the last 16 years of this long-term study.
Measurement of various soil physical properties after 22 years on a Fargo silty clay soil showed that bulk density (BD) values ranged from 0.9 g/cm3 in the surface 6-inches to 1.3 g/cm3 in the lower 30-48 inch depth. Although differences in BD were not dramatic, the no-till system consistently had lower values throughout the profile. The grass area had slightly higher BD values in the upper 12-inches, while the plow and chisel systems had increased BD in the 18 to 36-inch depths. The actual soil weight with no-till, based on BD, accumulated down the profile was 48, 200, 297 and 275 thousand lbs/acre lower than the plow for the respective 0-12, 0-24, 0-36 and 0-48 depths. This definitely indicates that the soil on the plow system (intensive tillage) has become more compact, either the result of organic matter loss and/or axle weight of tillage passes. Less tillage with the chisel system showed a moderate decrease in weight from 20 to 40 thousand lbs/acre.
The percent dry aggregates on the grass measured by a rotary sieve at the large sizes (greater than 2 mm) were generally the highest and decreased as the degree of tillage increased. Conversely, the aggregates on the grass less than 2-mm were low in percentage and increased with tillage. The percentage of wind erodible aggregates averaged 6% on the grass and increased to 13%, 23% and 24% for the no-till, chisel, and plow system, respectively. No wind erosion would be expected on the grass area with 100 percent cover throughout the year. The no-till soil would experience little wind erosion with the 45% and 76% cover after planting except when the pea residue was cultivated with a tandem disk in 2000, and only 8% cover was observed after planting. A portion of the aggregates with the chisel system may be subject to wind erosion, especially in 2000 where the pea residue was reduced to 7% with only one tandem disk operation. The higher portion of erodible aggregates on the plow system, along with low residue cover values, makes this system highly susceptible to wind erosion during dry-windy conditions.
Water infiltration rates varied considerably between years, and among residue management systems, and were dependent on initial soil moisture. Soils were fairly dry in both the spring and fall when infiltration rates were determined, as values ranged from 25% on the grass to 37% on the no-till. This Fargo soil has a 15 and 1/3 bar moisture content of 28% and 50%, respectively. Infiltration on the plow in the spring of 2000 (previous crop field peas) averaged 141 in/hr and decreased to 14 in/hr when a second inch of water was applied to the wet soil. No-till infiltration was considerably lower at 27 and 4 in/hr, respectively. However, spring infiltration rates, both dry and wet, were similar in 2001 (previous crop durum wheat) between plow and no-till (195 vs. 170 in/hr and 13 vs. 8 in/hr). In the fall when soils were much dryer, the infiltration rate on the plow was exceptionally high at 673 in/hr and quite variable. Even the fall 2000 wet infiltration rate on the plow system was 150 in/hr. Fall 2000 no-till infiltration was 115 in/hr dry and 25 in/hr wet. In the fall of 2001, infiltration rates averaged 210 in/hr for both plow and no-till. The infiltration rate on the no-till was similar among years and season, while the plow system showed large variability and fluctuations. The soil type can explain this large variation in infiltration rates on the plow system. The Fargo soil has a high content of clay that exhibits large shrink-swell actions with wetting and drying that leaves large cracks as the soil dries. These cracks are more prevalent under intensive tillage systems like plow. As a comparison, the initial infiltration rate on the grass with 1-inch of water in the fall of 2000 was 282 in/hr and decreased to 91 in/hr, as the soil was wetted. Infiltration rates were not determined on the chisel system, but we feel the values will range somewhere between the plow and no-till systems.
Biological activity in the soil was evaluated by measuring earthworm, bacteria, and fungi populations. Earthworms on the grass site on May 31 in 2001 averaged 792 thousand, consisting of 625 thousand adults and 167 thousand cocoons per acre. Plow and chisel systems had slightly higher total earthworms than the grass at 937 and 1,083. No cocoons were found on the plow system, indicating that all cocoons had hatched and no additional reproduction had occurred by sample time. The higher earthworm number on the chisel is associated with less tillage and better survival moisture conditions with increased surface residue cover. The 42,000 cocoons per acre found with the chisel system may be due to increased reproductive activity with better earthworm conditions or the surface residue cover created cooler soil temperatures and the cocoons had not hatched by the time of sampling. The average total earthworm population with no-till was 1,896,000 per acre. This was double the plow system. The high numbers with no-till are associated with better environmental conditions, that is, cooler temperatures, greater soil moisture, and an adequate residue food source. Earthworms also like a high nitrogen environment that is enhanced by placing a legume in the rotation or adding nitrogen as fertilizer. The increase of over 900,000 adults with added nitrogen on the no-till system demonstrates this principle. The reason for the lower number of earthworms on the plow and chisel with added nitrogen is not clear, but may be associated with the greater earthworm activity at the time tillage is performed since tillage usually decreases populations when earthworms are active in the spring or fall. As part of the objectives, an attempt was made to look at vesicular arbuscular mycorrhizae (VAM) on the roots extracted from the Fargo soil, which has a very high clay content. It was difficult to extract good root specimens from this soil. Vesicles were observed in the root samples with a microscope, but it was difficult to determine if any differences occurred among systems on the samples collected.
Bacteria that decompose both inorganic and organic material, and fungi that break down organic matter, dominate the soil microbial environment. Bacteria populations on the plow system were similar (40,000 colonies/gram soil) at the 0-3 and 3-6 inch depths without N fertilizer, but were much lower in the 0-3 inch depth (3,000) and higher (over 1 million) in the 3-6 inch depth (area in the soil where residue buried by tillage) when N fertilizer was applied. In comparison with the plow system, no-till soil, without N fertilizer, contained the highest bacteria population at 180 million in the 0-3 inch depth where most of the residue is deposited. Only 30,000 colonies were measured in the 3-6 inch depth. Bacteria populations in the soil were only in the 20,000 to 30,000 range where N fertilizer (120 lbs/acre) was applied. The reason for this lower population is unclear, but may be related to the fact that the added nitrogen produced an early high population, which depleted the food supply, and populations returned to a stable number by the time samples were collected to be evaluated. Fungi populations on the plow system ranged from 20,000 to 70,000 colonies per gram of soil. Fungi populations, like the bacteria, were higher in the 3-6 compared to the 0-3 inch depth. Fungi populations tended to be slightly higher (10,000 to 20,000) when N fertilizer was applied. Populations of fungi on no-till were generally lower than the plow system, except for the 0-3 inch depth without nitrogen where the colonies were six times higher at 120,000 colonies per gram of soil.
Some chemical properties of the soil under grass and three residue management systems were changed over the 22 years of this long-term study. The 1:1 soil pH on the plow system in the upper 12 inches increased to around 7.9 to 8.1 when compared to the grass and other two residue management systems (7.7 to 7.8). This increase was associated with moving the carbonates nearer the surface with 8 to 10 inch deep tillage every other year. Soil on the grass below 18 inches ranged from 8.1 to 8.3, while the three residue management systems (plow, chisel and no-till) contained pH levels in the 7.8 to 8.2 ranges. The electrical conductivity (EC) of the grass area ranged from 1.5 to 4.0 mmoles/cm in the upper 12 inches of the profile, and remained from 4.0 to 5.0 at the lower depths in the profile. Cultivation reduced the EC values at all profile depths when compared to grass. Under the plow system, EC averaged around 1 in the upper 12 inches, then steadily increased with depth to a value of 3.5 at the 48-inch depth. The lowest EC values were obtained on the no-till system, usually 1 or less to 24 inches, then a gradual increase to 2.5 mmoles at 48 inches. Surprisingly, the chisel system (reduced tillage) had EC values between the plow and no-till. This indicates that over a period of years, EC values can be reduced by less tillage, which allows greater movement of salts to lower depths in the profile beyond 48 inches.
Organic matter (OM) content in the surface 6 inches of the soil on the grass ranged from 5.5% to 6.5%. Extensive tillage with the plow had reduced OM levels below 5%. OM levels at this depth were around 5.0% to 5.5%. The OM levels measured below 6 inches was similar among the systems, however, higher OM was observed on the no-till between the 18 to 36 inch depths in the profile. OM total on the grass ranged from 40,000 to 45,000 pounds in the upper 6 inches. Plow ranged from 30,000 to 35,000 pounds. This loss amounted to over 19,000 pounds of OM in the 0-12 inch depth with intensive tillage like the plow system. By going to no-till, some 4,700 pounds of OM were returned to the upper 12 inches of the soil. If one compares the various systems and includes the lower depths (0-24, 0-36 and 0-48 inches), the differences in OM were much less. The no-till system actually contained more total OM than the grass when the 0-36 and 0-48 inch depths are compared.
The phosphorus (P) levels measured in the soil profile were consistently highest on the no-till, followed by the plow system. P levels on the chisel and grass area were similar. In the upper 18 inches, the no-till was 1 to 2 ppm higher than the plow. Phosphorus total on the grass at the 0-3 inch depth was less than 5 lbs/acre, dropped to 2 lbs/acre in the 3-6 and 6-12 inch depths, then gradually increased to 4 lbs/acre at the 42-48 inch depths. No-till, plow, and chisel systems had peak P total levels at the 0-3 and 6-12 inch depths that were not present on the grass area. These peaks on the cultivated systems can be attributed to surface and deep band applications of phosphorus fertilizer in the fall of 1987. The extractable P total accumulated down the profile (0-12, 0-24, 0-36 and 0-48 inch depths) followed the same pattern with no-till>plow>chisel=grass.
Potassium (K) levels in the profile averaged from 300 to 500 ppm in the upper 12 inches. K levels on the no-till and grass tended to be higher at the 0-3 inch depth than the plow or chisel systems but lower than the plow at the 3-6 and 6-12 inch depths. Below 18 inches the K levels ranged from 200 to 300 ppm with the sequence no-till>plow>chisel>grass. K total in the surface 0-3 inch depth ranged from 270 to 310 lbs/acre with a depletion zone in the 3-6 inch depth on all systems (range 210 to 260 lbs/acre) and a large increase from 400 to 450 lbs/acre at the 6-12 inch depth. A large decrease in exchangeable K was observed on the grass area at the 18-30 inch depth. Below 18 inches the K total ranged from 350 to 400 lbs/acre with no-till>plow>chisel. However, if one compares total exchangeable K in the various profile depths, other than the grass and chisel the lowest, systems were similar with an average around 960, 1640, 2400 and 3160 lbs/acre, respectively for the 0-12, 0-24, 0-36 and 0-48 inch profile segments.
The levels of exchangeable calcium (Ca) on the grass area were much lower than the three residue management systems with levels around 2,300 ppm in the surface 3 inches, and gradually increased with depth to 3,300 to 3,800 ppm at 18 to 36 inches and reached 6,500 ppm at the 48 inch depth. Ca levels on the plow, chisel, and no-till systems ranged from 3,700 to 4,700 ppm in the 0-36 in profile depth, and then increased to around 5,500 ppm at the lower depths. More exchangeable Ca was measured on the plow system in the upper 24 inches of the soil compared to the chisel and no-till. Calcium total in the 3 and 6 inch depths ranged from 2000 to 3000 lbs/acre in the sequence plow>no-till=chisel>grass. Ca levels (6,000 lbs/acre) were similar among systems at the 12-inch depth. At the 18 to 42 inch depth ranges, the three residue management systems contained Ca from 7,000 to 9,000 lbs/acre. A comparison of Ca levels accumulated down the profile showed levels for grass, plow, chisel, and no-till to be 21,000, 27,000, 25,000 and 24,000 lbs/acre in the 0-24 inch profile and 51,000, 62,000, 59,000, and 58,000 lbs/acre in the 0-48 inch profile, respectively.
The exchangeable magnesium (Mg) levels on the grass area were around 600 ppm in the surface 3 inches and increased to 1,000 ppm at 18 inches and remained around this level at the lower profile depths. The Mg levels measured on the plow, chisel, and no-till systems were similar down the profile, but were consistently 600 to 700 ppm higher than the grass area. Exchangeable total Mg in the surface 6 inches on the grass area averaged around 500 lbs/acre, while the cultivated systems had Mg values of 800 to 1,000 lbs/acre. Maximum Mg values on the grass reached 1,800 lbs/acre at 30 inches while the plow, chisel, and no-till reached 3,200 lbs/acre at this same depth. The accumulated total exchangeable Mg in the 0-48 inch depth reached around 22,000 lbs/ac on the three cultivated areas, but reached only 12,000 lbs/acre on the grass area.
The exchangeable sodium (Na) levels in the grass ranged from 400 ppm in the surface and gradually increased to a maximum of 1,700 ppm at 30 inches. The Na levels on the plow, chisel, and no-till were less than 200 ppm in the surface and increased with depth to reach maximum values of 800 to 1,100 ppm at the 48-inch depth. It is interesting to note that among the three tillage systems, plow had the highest Na concentration and the levels decreased at all depths as the degree of tillage was reduced. Therefore, chisel had Na levels around 200 ppm less than the plow, and the no-till had Na levels around 100 ppm less than the chisel. The amount of total sodium in the profile followed the same pattern. The total exchangeable sodium in the 0-12 and 0-24 inch depths on the grass amounted to 2,900 and 7,800 lbs/acre, respectively. Total sodium in these same depths was 850 and 3,300 lbs/acre for the plow, 500 and 1,100 for the chisel with only 400 and 1,600 lbs/acre for no-till. It would appear that cropping this soil has reduced the Na levels in the soil through improved soil structure and water movement to reduce Na movement upward from the lower levels, or the crop seed is removing Na over the 22 years of this study. It also indicates that less tillage with no-till and chisel has a greater impact on reducing Na levels in the soil profile when compared to intensive tillage like the plow system. Less tillage retains more surface cover thus less evaporation and upward movement of Na with the water loss.
Zinc (Zn) levels in the soil that often correlate with organic matter levels in the soil were highest on the grass. In the surface 6 inches, ppm Zn in the grass soil ranged from 0.7 to 1.2 with lower values in the cropped systems. The surface 0-3 inch depth contained extractable Zn levels of around 0.7, 0.6 and 0.5 ppm for the respective no-till, chisel, and plow. Zn levels at the 6 to 18 inch depth range were similar among the systems, but varied between systems at the lower soil profile depths. The total extractable Zn, although less than 0.5 lbs/acre, tended to be slightly higher in the no-till in the 0 to 12 inch depth than the plow or chisel. The plow and chisel systems had higher Zn levels at the lower depths. If one compares the accumulated Zn in the profile, the grass contains the most Zn at 1.8 lbs/acre with the no-till (1.2 lbs/ac) and both plow and chisel at 1.1 lbs/acre in the surface 12 inches. It should be pointed out that Zn deficiency was observed and documented early in the season on this Fargo soil with the plow system when grain legumes (soybean, edible dry bean, and field pea) were grown, but Zn deficiency was not found on the no-till system. This difference is more related to availability than extractable amounts. Higher pH reduces Zn availability, and the plow system contained higher pH levels in the surface soil than no-till.
Iron (Fe) levels in the soil were 2 to 3 ppm lower on the grass area throughout the profile compared to the three cultivated systems. Fe levels in the plow system ranged from 9 to 11 ppm in the 0-48 inch profile. Extractable Fe on both no-till and chisel were usually 1 to 2 ppm lower than the plow system. Total Fe on the grass ranged from 4 lbs/acre in the surface to 10 lbs/acre at depths below 42 inches. Around 6 lbs/acre were found in the upper 6 inches of the plow, chisel, and no-till systems, and increased to above 12 lbs/acre at 12 inches and the lower depths. Below 12 inches the amount of Fe on the plow system was always 1 to 2 lbs/acre higher than either chisel or no-till. The accumulated total Fe in the 0-24 inch increment depth on the grass was measured at 28 lbs/acre and nearly doubled on the no-till (50 lbs/acre), chisel (49 lbs/acre), and plow (56 lbs/acre) systems. It should be noted that Fe deficiency was observed on soybeans grown on the plow system but not on the no-till system. Even though the plow system contained higher extractable Fe levels the difference in deficiency is again related to availability to the plant that is controlled by wet soil conditions or internal drainage problems, decreased aggregation, and carbonate levels. The inorganic carbon levels were much higher in the surface of the plow system. Also the Fe deficiency occurred early during wet springs and the soils remained saturated above the tillage layer in the plow system due to a possible tillage pan or poor soil structure on this high clay content soil. The no-till system, with better internal drainage resulting in part to increased earthworm activity and movement of carbonates to lower depths, did not experience Fe deficiency.
Manganese (Mn) levels in the surface 6 inches ranged from 4 to 6 ppm. The no-till system had the highest level while the plow system contained the lowest Mn level. Mn levels in the 6-18 inch increment were similar, but below 18 inches the plow contained the highest levels while the grass contained the lowest Mn levels. The extractable total Mn in the surface 0-3 inches was 4 lbs/acre on the no-till, but only 3 lbs/acre on the plow. The highest total Mn values were found in the 6-12 inch increment, nearly 5 lbs/acre in the no-till system. Total Mn below 18 inches was around 2 lbs/acre on the grass, but ranged from 2 to 5 lbs/acre in the sequence plow>chisel>no-till. The total Mn accumulated in the 0-36 inch increment averaged 18 lbs/acre in the grass, and increased to 22, 22 and 24 lbs/acre for the no-till, chisel, and plow systems, respectively.
Another trace element, copper (Cu), often associated with organic matter, was highest in the plow system throughout the soil profile, ranging from 1.5 ppm in the surface to greater than 2.5 ppm below 30 inches. The grass area had lower Cu levels than chisel or no-till in the upper 18 inches but had similar values below 18 inches. Total Cu in the upper 6 inches (1 lbs/acre) and 6-12 inch depth (2.5 lbs/acre) was similar among the four systems. Cu values below 12 inches varied among the systems. and ranged from 3 to almost 5 lbs/acre. The accumulated total Cu in the 0-48 inch increment depth was 26, 27, 28 and 30 lbs/acre, respectively, for the grass, no-till, chisel, and plow systems.
A comparison of organic carbon percentages shows from 3.2% to 4.0% on the grass in the surface 6 inches, while the no-till and chisel in the range of 2.6% to 2.8%, and the plow the lowest at less than 2.5%. Organic carbon below 12 inches was similar. Total organic carbon in the upper 6-inches ranged from 23,000 to 27,000 lbs/acre on the grass. The plow, chisel, and no-till showed lower total carbon values near 15,000, 17,000, and 18,000. The accumulated total organic carbon in the 0-6 inch depth was 50,300, 32,300, 35,100 and 35,800 lbs/ac for the grass, plow, chisel, and no-till, respectively. The total organic values in this study are much lower than the values estimated by Cihacek and Ulmer (1995) in 6-inches of various soils, or Bauer and Black (1983) in 18 inches in a fine textured soil for other North Dakota soils. The carbon levels in Saskatchewan Canada at this same depth were much lower under conventional (28,000 lbs/ac) and no-till (30,000 lbs/ac) systems (Campbell, et al., 1995). All systems showed a spike in total organic carbon at the 6 to 12 inch depths, with similar values below. Total organic carbon on the grass area in the 0-24 inch depth amounted to slightly less than 109,000lbs/acre. The amount found in the plow, chisel, and no-till was lower 91,000, 94,000, and 98,000, respectively. The total organic carbon found in the profile at the grass area, predominantly blue grass, was much lower than that recorded by Cihacek and Meyer (2002) under bromegrass with the same soil.
The inorganic carbon in the 0-6 inch depth was the highest with the plow system at around.0.4 to 0.5 percent. Grass, chisel, and no-till contained similar levels at 0.2% to 0.3%. A large peak in inorganic carbon appeared in the 18 to 30 inch depths with grass (2.5%), chisel (2.3%), and plow (2.0%) higher than the no-till (1.7%). The lower inorganic content with no-till was also associated with similar levels of inorganic carbon at the 36 to 48 inch depth, while the levels on the plow, chisel, and grass were well below 1.5%. This indicates that the inorganic carbon on the no-till is being moved downward as the levels above decrease. The inorganic carbon levels on the grass, plow, and chisel remain rather constant at the 18 to 30 inch depth. The inorganic carbon total for all systems was less than 5,000 lbs/acre in the upper 6 inches of soil, and increased to 35,000 lbs/acre at the 18 to 30 inch depth of the plow, chisel, and grass. No-till contained less than 30,000 lbs/acre of inorganic carbon at this depth range, and remained constant at the lower profile depth. Inorganic carbon total on the plow, chisel, and grass area were lower than no-till at these lower depths, usually less than 25,000 lbs/acre. If one looks at inorganic carbon accumulations down the profile, the grass ranges from 16,000 lbs/acre in the 0-12 inch profile, to 200,000 lbs/acre in the 0-48 inch profile. Inorganic carbon for these same depths was 21,000 and 190,000 for the plow with 19,000 and 200,000 for the chisel. The amount of total accumulated inorganic carbon on the no-till averaged much less: 14,000 at 0-12 inch and 170,000 lbs/acre in the 0-48 inch profile. The total inorganic carbon in the profile measured in this study was higher than that found stored in other North Dakota soils (Cihacek & Ulmer, 2002).
Percent total carbon (inorganic + organic) followed similar trends among the systems as previously discussed. Total carbon accumulations in the 0-48 inch profile amounted to 351,000, 332,000, 348,000, and 329,000 lbs/acre for the grass, plow, chisel, and no-till systems, respectively.
The percent total nitrogen (N) in the soil profile ranged from 0.45 in the surface 0-3 inches to 0.05 at the 42-48 inch depth. The grass area contained the highest N percentage down the profile and the lowest N percentage was found under the plow system. The total N in the surface 0-6 inches ranged from 2,700 to 3,200 lbs/acre on the grass area. No-till and chisel contained around 2,000 lbs/acre, while soil in the plow system measured at around 1,800 lbs/acre. A large peak of N was found on all systems at the 6-12 inch depth, with values running from a low of 3,000 lbs/acre on the plow to a high of 3,700 lbs/acre with grass, and both no-till and chisel in the middle, at around 3,400 lbs/acre. Total N accumulated down the profile on the grass averaged 9,560, 14,640, 18,880 and 22,000 lbs/ac for the 0-12, 0-24, 0-36, and 0-48 inch increments, respectively. Comparing the grass with the plow system shows that 2,780, 3,630, 4,670, and 5,310 lbs/acre of N was lost by cultivation with intensive tillage. It should be pointed out that some of this N loss may have occurred prior to the initiation of this long-term study because the site was cultivated for five years since the grass area was first cultivated. This loss may even be greater since nitrogen fertilizer was added to the plow system every other year, starting in 1997 and grain legumes that can fix N from the atmosphere were grown every other year starting in 1987. By going to less tillage with the chisel and no-till, the loss of N was considerably less. Total N loss in the no-till system was 2,080, 2,260, 2,560 and 2,650 lbs/acre at the respective 0-12, 0-24, 0-36, and 0-48 inch depth increments. If one compares the plow system with no-till, an average increase of N at these same increments amounted to 700, 1,370, 2,110 and 2,660 lbs/acre of N were gained by converting to a no-till system. The N gained by using the reduced chisel system in place of the plow was a moderate 700, 1,230, 1,730 and 2,090 lbs/acre. The total N accumulated in the 0-18 inch depth of the plow (9,000 lbs/ac) and chisel (10,000 lbs/ac) were very similar to values reported by Bauer and Black (1983) for conventional and reduced tillage small grain-fallow systems from North Dakota. The total N in the 0-6 inch depth for plow (3,770 lbs/ac) and no-till (4,100 lbs/ac) was much higher than the soil levels (3,100 lbs/ac) with conventional or no-till systems under spring wheat reported in Saskatchewan Canada by Campbell, et al. (1995).
The evolution of carbon dioxide was measured at various times during the cropping season using a portable environmental gas monitor (EGM-2). Measurements were taken around the 15th of each month. Data was collected starting in 1999 and continued in 2000 and 2001. The 2000 results were discarded because large fluctuation occurred in the data, which turned out to be equipment failure that required repair before sampling could continue. The amount of gas evolved varied with time of year and system, and was generally related to soil temperature and moisture. The amount of carbon dioxide released decreased as soil moisture decreased, and increased with increasing soil temperature, unless soil moisture was low. The average carbon dioxide release was usually lower with no N fertilizer compared to when fertilizer was applied. The grass area had carbon dioxide values that ranged from 0.26 (September 2001) to 1.35 grams per square meter per hour (June 1999). Plow, chisel, and no-till had maximum values of 1.61, 1.22, and 1.28 grams, which occurred in June 1999 when decomposition of carbon was rapid. However, in 2001 the maximum rates were measured in July with 1.11, 0.74, 0.66, and 0.62 grams for the grass, plow, chisel, and no-till systems, respectively. The lowest loss of carbon usually occurred in August of 1999 and September in 2001. The slightly higher release of carbon on the grass during the middle of the summer compared to the three cultivated sites may be related to better soil moisture and warmer soil temperatures with less growth and the shorter height of the grass plants. The carbon loss for grass, plow, chisel, and no-till systems, averaged across the season of both years, was measured at 0.70, 0.61, 0.49, and 0.48 grams, respectively. Reicosky (2002) reported similar fluctuations over time in carbon dioxide flux values on tilled and untilled loam soils. In this study, the amount of carbon dioxide released to the atmosphere was not always related to the amount of C or OM in the soil or system, but depended more on the time of year and/or plant growth and dry matter produced that subsequently affected soil moisture and temperature, which altered biological activity and the mineralization rate of C.
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This two-year study, which looked at long-term changes in soil properties under three residue management systems compared to grass, showed some interesting results. The plow system showed a greater degradation of soil quality indicators than the chisel did, while the no-till system improved many indicators. Although some differences occurred for specific profile depths, results indicated that physical properties like bulk density or weight were not greatly different after 22 years (averages values around 1.0 g/cubic cm in upper 6-inches and 1.1, 1.2 and 1.3 in the lower 6-12, 12-24 and 24-48 inch depths). Soil weight did not change among grass or tillage system, and had a total average weight of around 13 million pounds in the 0-48 inch profile depth. Infiltration rates varied among systems, years, and time of year, but initially the averages in this study were more rapid on the tilled plow system (304 in/hr) and grass (282 in/hr) than the no-till system (130 in/hr). After the soil was wetted with one inch of water, the infiltration rates were considerably lower and similar among the systems (48, 91 and 15 in/hr). The percentage of erodible soil aggregates (< 2mm) increased with degree of tillage with the sequence: grass (6%), no-till (13%), chisel (23%), and plow (24%). The average surface cover measured on the grass was 100%, while cover after planting on the no-till, chisel, and plow systems were, respectively, 76%, 39%, and 4% after planting field peas into small grain residue. Grain legumes, without fall tillage, only provided 46%, 27%, and 22% cover on the no-till, chisel, and plow systems after planting small grain into grain legumes. Fall tillage of grain legumes left less than 10% residue cover after planting, irrespective of tillage system. The low surface cover and high erodible aggregates on the chisel and plow subjected the soil to wind erosion. Biological measurements of earthworm population showed a large increase on no-till with an average around 1.9 million/acre but only half this number on the grass (0.8 million), chisel (1.0 million), and plow (0.9 million). This indicates that soil disturbance at the time of earthworm activity, spring or fall, and a reduction in surface cover inhibits earthworm activity and reproduction. The similar or slightly higher earthworm numbers on the plow and chisel compared to the grass area may be attributed to the introduction of a legume into the rotation which enhances earthworm activity when compared to a non-legume situation. This study indicated that bacteria and fungi populations varied with depth and between tillage systems. The overall average bacteria colonies per gram of soil in the 0-6 inch depth were increased by no-till (45 million) compared to plow (300,000). The average fungi count was similar among plow and no-till at around 47,000 per gram of soil. One of the most significant observations in this trial was that both total N and organic C were lost in the soil profile when comparing tillage systems with grass. Plow reduced N by 5,300 lbs/acre and C by 11,000 lbs/acre over 22 years. Reduction by switching to a chisel plow system was 3,200 lbs N/acre and 3,900 lbs C/acre. Going to a no-till system with no primary or secondary tillage reduced the loss further, 2,600 lbs N/acre and 400 lbs C/acre. This indicates that producers are capable of large savings in N and C by reducing tillage. Over the years of this study, both iron and zinc deficiency were consistently observed on the plow system when grain legumes (soybean, dry bean, and field pea) were grown. Due to improved physical (internal drainage or hydraulic conductivity), biological (earthworms, bacteria) and chemical (carbonates) conditions, iron and zinc deficiency were not observed on the reduced tillage systems (chisel and no-till). A second finding of significance in this study was the impact of various systems on sodium levels in the soil profile. Cultivation of the soil in this long term small grain/row crop rotation reduced the levels of Na throughout the profile when compared to the grass area. Na levels in the profile followed the same sequence as amount of tillage with plow>chisel>no-till and the difference among systems increased as depth in the profile increased. That is, after 22 years, the total Na in the 0-48 inch profile was decreased some 8,700 lbs/ac with plow, 11,500 lbs/ac with chisel, and 12,800 lbs/ac with no-till compared to the grass area. This change in Na is partially due to crop removal (none removed by the grass), but mainly due to improved soil structure and surface cover differences that controls water movement up and down the profile, which varies among the plow, chisel, and no-till systems. We believe the sodium results in this study have not been previously documented under tillage system comparisons.
No direct economic analyses were performed because this was not a part of the objectives, and it is difficult to assess the overall benefits or improvements in the physical, chemical, and biological properties, currently referred to as soil quality. The reason for the difficulty is that producers and economists currently give little value to the soil and associated properties. The soil is usually considered to have value only if it is sold, and in most cases the soil is considered a liability since it is added to the expense side of the equation since taxes are paid on the soil. Currently the trend is to tax better soils at a higher rate because these soils provide more income. Maybe the trend should be reversed and more taxes are assessed when soils are allowed to deteriorate with extensive tillage and/or erosion. The economic gain or loss due to increases or decreases in the physical and biological properties is difficult to evaluate since so many variables are influenced by changes in these properties. Although the chemical properties are also influenced by the physical and biological conditions, some of these properties might be easier to evaluate. For example, what is the value of nitrogen, a major input into most crop productions systems? If one compares the total N in the grass at the 0-48 inch depth to the plow system, what is the 5,310 lbs/acre (241 lbs/acre/yr) difference or loss worth? At current prices of 20 cents/lb of N, it would take $1,062 per acre (above $48/yr) to replace the N loss due the intensive plow tillage system. By going to no-till, over the 22 years, the loss would be about one half or only $530 per acre. The question always arises, is this saving worth changing tillage systems? Carbon is another chemical property that has value because it also influences the other physical and biological properties. There is interest in storing carbon in the soil as a sink to reduce carbon dioxide in the atmosphere with payments for the amount of carbon stored. Unfortunately at this time, the value of this stored carbon has yet to be determined (McConkey, et al., 1999). If one looks at only organic carbon, cultivating the grass for 22 years with the plow system has decreased organic carbon in the 0-48 inch soil depth by 11,050 lbs/acre. This released carbon contributes to the “green house effect.” Switching to no-till retained most of the carbon in the soil, as the grass and no-till contained 151,620 and 151,235 lbs/acre, respectively. What is this 10,660 lb/acre carbon stored in no-till worth? Something that needs to be determined to help evaluate soil properties.
Adoption of any tillage system(s) by producers based solely on improvements in soil properties, especially on new research information, has shown in the past to be very slow because of resistance to change. Most producers want quick fixes rather than slow changes, but fail to realize that the overall benefits of improved soil properties require longer periods of time. The benefits shown in this research study — especially the savings in carbon and nitrogen, potential for less plant deficiency problems, reduction in salinity problems, and reduced soil erodibility — will likely be rapidly adopted by innovative producers, while others will be slow adopters because of their attitudes or financial restraints.
Educational & Outreach Activities
Information collected in this evaluation of soil property changes after 22 years will be provided to the North Dakota State University (NDSU) Extension service, North Dakota Research/Extension Center, and North Dakota National Resource Conservation Service (NRCS). We hope this information will be used in developing soil quality fact sheets and bulletins for producers, presenting talks to the general public, or provide training to new and/or established employees. This complete final report, with tables and figures, will be made available on the NDSU Soil Science Department web site for interested producers and research personnel. This site is located at http://www.soilsci.ndsu.nodak.edu/deibert/deibert.html#publications
Areas needing additional study
Hopefully the database provided by this research will provide information on the long-term effects that residue management systems have on the chemical, physical, and biological properties of the soil and those positive impacts will direct future soil quality research. Chemical properties and associated changes are easier to measure and assess when compared to the physical and biological properties. Improved physical and biological properties were observed on this long-term study, but there is a need to develop techniques to measure these gains over a shorter period of time and then place a value on the improvements that can be used to quantify the benefits of any particular system. Concurrently the value of sequestered C, N and other improvements (reduce erosion potential, correct plant nutrient deficiency problems, lower salinity, improved internal drainage) must be established and this value entered into the economic equation as a positive, that is, considered to be income. There is also a need to study the impact of the addition of new crops (example: canola, borage, and coriander) to the rotation and their long-term impact on soil properties.