Soil Compaction and Agricultural Production: A Review

Transcription

1 Proceedings of the International Soil Tillage Research Organisation (ISTRO) Nigeria Symposium, Akure 2014 November 3-6, Akure, Nigeria. Soil Compaction and Agricultural Production: A Review. Baker Soil Compaction and Agricultural Production: A Review Baker, A.T Land and Water Management Engineering Department, National Centre for Agricultural Mechanization, Ilorin bakeradebayour@gmail.com Abstract Soil compaction is not considered a widespread, serious problem in Nigeria. However, soil compaction can be a serious and unnecessary form of soil degradation. Preventing soil compaction is far better than trying to correct a compaction problem after it occurs. Soil compaction is the physical condition of the soil by an applied force that destroys structure, reduces porosity, limit water and air infiltration, increases resistance to root penetration and often results in reduced crop yield. Most farmers are aware of compaction problems but the significance is often underestimated. Compaction effects on crop yield can be a significant factor in today's farm economy. A typical silt loam contains about 50% pore space, portioned at 25% water 25% air by volume at field moisture capacity. Soil particles and organic matter occupy the remaining 50%. Soil compaction is a process that first occurs when the force from wheel traffic pushes aggregates together. The problem of soil compaction is increasing for several reasons. Earlier planting schedules, larger equipment, and increase use of duals or floatation tires that encouraged field operations on wetter soils are all responsible. Wheel traffic from heavy farm equipment is recognized as the major cause of soil compaction, although some compaction occurs from normal crop production practices. The major effect of compaction is an increase in bulk density as soil aggregates are pressed closer together, resulting in a greater mass per unit volume. Compaction reduces the soil pore volume, resulting in less space for air and water in the soil. Increased bulk density and reduced pore volume also reduce the water infiltration into the soil. Compacted soil can cut crop yields by as much as 50% due to reduced aeration, increased resistance to root penetration, poor internal drainage, and limited availability of plant nutrients. Proper tractor and machine set up and operation can minimize the effect of compaction, but improved management is the best solution for addressing compaction. Keywords: water and air infiltration, compaction, bulk density. 1. Introduction Soil compaction problems were experienced in commercial production long before any coherent research was undertaken on this topic. ( Soane, 1994), The introduction of the internal combustion engine for small tractors did not initially lead to widespread compaction problems but by the middle of the 20th century, and particularly during the past 30 years, mechanization has advanced to such a scale and intensity that compaction problems have become of worldwide importance. ( Moncrieff, 1983) Soil compaction is now considered to be a multidisciplinary problem in which machine/soil/weather interactions play an important role and which may have serious economics and environmental consequences in world agriculture. However, recent progress in scientific understanding of the soil compaction process and its implications improved insight into proper 182

2 Proceedings of the International Soil Tillage Research Organisation (ISTRO) Nigeria Symposium, Akure 2014 November 3-6, Akure, Nigeria vehicle use and soil management, and the development of mechanization systems novel running gear, provide new perspective for reducing soil compaction problems in crop production. Soil compaction can be a serious and unnecessary form of soil degradation that can result in increased soil erosion and decreased crop production. Compaction of soil is the compression of soil particles into a smaller volume, which reduces the size of pore space available for air and water. Most soils are composed of about 50% solids (sand, silt, clay and organic matter) and about 50% pore spaces. ( Bailey, 1986) As farm tractors and field equipments become larger and heavier, there is a growing concern about soil compaction. Soil compaction can be associated with a majority of field operations that are often performed when soils are wet and more susceptible to compaction. Heavy equipments and tillage implements can cause damage to the soil structure. Soil structure is important because it determines the ability of a soil to hold and conduct water, nutrients, and air necessary for plant root activity. Although much research has been conducted on soil compaction and its effect on yield, it is difficult to estimate an economic impact because fields vary in soil types, crop rotations, and weather conditions. Soil compaction is the physical condition of the soil by an applied force that destroys structure, reduces porosity, limit water and air infiltration, increases resistance to root penetration and often results in reduced crop yield. Compaction effects on crop yield can be significant factors in today's farm economy. Recent changes in agricultural practices (such as increased number of operations and larger equipment) have made soil compaction more common. Most yield-limiting compaction is caused by wheel traffic from heavy equipments, often when operations are conducted on wet soils. Soil compaction is a process that first occurs when the force from wheel traffic pushes aggregates together. The major effect of compaction is an increase in bulk density as soil aggregates are pressed closer together; resulting in a greater mass per unit volume compaction reduces the soil pore volume, resulting in less space for air and water in the soil ( Soane, 1994) 1.1 Problems of Soil Compaction on Agricultural Production This paper reviews the work related to soil compaction, agricultural production, concentrating on the research that has been done in the ten years. Several approaches have been suggested to address the soil compaction problem, which should be applied according to the soil, environment and farming systems. The following practical techniques have emerged on how to avoid, delay or prevent soil compaction. (a) reducing pressure on soil either by decreasing axle load and /or increasing the contact area of wheels with the soil; (b) working soil and allowing grazing at optimal soil moisture; (c) reducing the number of passes by farm machinery and the intensity and frequent of grazing; (d) confining traffic to certain areas of the field ( controlled traffic); (e) increasing soil organic matter through retention of crop and pasture residue; (f) removing soil compaction by deep ripping in the presence of an aggregating agent;(g) crop rotations that include plants with deep, strong taproots; (h) maintenance of an appropriate base saturation ratio and complete 183

3 Proceedings of the International Soil Tillage Research Organisation (ISTRO) Nigeria Symposium, Akure 2014 November 3-6, Akure, Nigeria. Soil Compaction and Agricultural Production: A Review. Baker nutrition to meet crop requirements to help the soil/crop system to resist harmful external stresses. 1.2 Consequences of Soil Compaction for Plant Growth Soil compaction can have both desirable and undesirable effects on plant growth Desirable Effects of soil compaction on plant growth Slightly compacted soil can speed up the rate of seed germination because it promotes good contact between the seed and the soil. In addition, moderate compaction may reduce water loss from the soil due to evaporation and, therefore, prevent the soil around the growing seed from dying out. A medium-textured soil having a bulk density of 1.2 grams per cubic centimeter (74 pounds per cubic foot), is generally favourable for root growth ( Note: a soil bulk density of 1.2 grams per cubic centimeter is comparable to a non-tracked soil after a secondary tillage operation). However, roots growing through a medium-textured soil with a bulk density near 1.2 grams per cubic centimeter will probably not have a high degree of branching or secondary root formation. ( Lewandowski, A. 1999). In this case, a moderate amount of compaction can increase root branching and secondary root formation allowing roots to more thoroughly explore the soil for nutrients. This is especially important for plant uptake of non-mobile nutrients such as phosphorus Undesirable Effects of Soil Compaction on Plant Growth Excessive soil compaction impedes root growth and therefore limits the amount of soil explored by roots. This in turn can decrease the plant's ability to take up nutrients and water. From the stand point of crop production, the adverse effects of soil compaction on water flow and storage may be more serious than the effect of soil compaction on root growth.(voorhees, 1994) In dry years, soil compaction can lead to stunted, drought stressed plants due to decreased root growth. Without timely rains and well-placed fertilizers, yield reductions will occur. Soil compaction in wet years decreases soil aeration. This results in increased denitrification (loss of nitrate-nitrogen to the atmosphere). There can also be a soil compaction induced nitrogen and potassium deficiency. 2. Causes of Soil Compaction There are several forces, natural and man-induced that compact a soil. This force can be great such as from a tractor, combine or tillage implement, or it can come from something as small as a raindrop. Listed below are several types of soil compaction and their causes. Raindrop Impact: this is certainly a natural cause of compaction and we see it as a soil crust (usually less than 1/2 inch thick at the soil surface) that may prevent seedling emergence. Rotary hoeing can often alleviate this problem. (Source: compaction - soil management series 2. University of Minnesota Extension, BU- 7400) Tillage Operation: continuous mouldboard ploughing or disking at the same depth will cause serious tillage pans (compacted layers) just below the depth of tillage in some soils. This tillage pan is generally relatively thin (1.2 inches thick), may not have a significant effect on crop 184

4 Proceedings of the International Soil Tillage Research Organisation (ISTRO) Nigeria Symposium, Akure 2014 November 3-6, Akure, Nigeria production, and can be alleviated by varying depth of0tlllage over time or by special tillage operations. Wheel Traffic: this is without a doubt the major cause of soil compaction. With increasing farm size, the window of time in which to get these operations done in a timely manner is often limited. The weight of tractors has increased from less than 3 tons in the 1940s to approximately 20 tons today for the big four-wheel drive units. This is of special concern because spring planting is often done before the soil is dry enough to support the heavy planting equipment. (Jones, 1999). The various forces of soil compression by agricultural equipment can cause soil particles to become compacted closer together into a smaller volume. As particles are compressed together, the space between particles (pore space) is reduced, thereby reducing the space available in the soil for air and water. The compaction force may cause the crushing of soil aggregates, which has a negative effect on soil aggregate structure. Be aware that compaction of agricultural soils can be caused by various farming practices: soil tillage that removes the protective residue from the soil surface, leaving the soil prone to natural environmental forces or excessive soil tillage that cause surface soil aggregates to breakdown or degrade, can lead to soil crusting, causing the surface soil layer to become hard and compacted. Soil tillage implements can induce soil compaction just below the depth of tillage, particularly when soils are wet the weight of large farm equipments (tractors, seed carts, combines, trucker, manure spreader) can cause wheel traffic compaction to a considerable depth within the root zone. As soil moisture content increases, so too the depth of soil compaction. (Voorhees, W.B 1986). 3. Compaction Effects Compaction concern- soil compaction can impair water infiltration into soil, crop emergence, root penetration and crop nutrient and water uptake, all of which result in depressed crop yield. Human-induced compaction of agricultural soil can be the result of using tillage equipment during soil cultivation or result from heavy weight of field equipment. ( Dejong-Hughes, 2001) Soil compaction can have a number of negative effects on soil quality and crop production including the following: Causes soil pore spaces to become smaller; reduces water infiltration rate into the soil; decreases the rate that water will penetrate into the soil root zone and subsoil; increases the potential for surface water pounding, water run-off, surface soil water logging and erosion; reduces the ability of a soil to hold water and air, which are necessary for plant root growth and function; reduces crop emergence as a result of soil crusting; impedes root growth and limits the volume of soil explored by roots; limits soil exploration by roots and decreases the ability of crops to take up nutrients and water efficiency from soil; and reduces crop yield potential. Compacted soil will restrict root growth and penetration into subsoil. This situation can lead to stunted, drought-stress plants as a result of restricted water and nutrient uptake, which results in reduced crop yield. (Alberta-Agricultural and Rural Development). 185

5 Proceedings of the International Soil Tillage Research Organisation (ISTRO) Nigeria Symposium, Akure 2014 November 3-6, Akure, Nigeria. Soil Compaction and Agricultural Production: A Review. Baker Best Management Practices to Prevent Soil Compaction Ideally, farmers should design their soil management and cropping practices to ensure the prevention of soil compaction.( Giles,1981). Use direct seeding practices to increase soil organic matter content, which will optimize soil structure; reduce the potential for the development of compacted soils by eliminating cultivation and reducing traffic in fields which will increase crop water use efficiency and increase crop yield potential; take advantage of the natural soil processes of "wetting-drying" and " freezethaw" cycles to minimize the effects of soil compaction. For irrigated areas, fall irrigation may ensure sufficient water for the freeze- thaw effects; use a combination of fibrous and tap rooted crops in a rotation to penetrate soil development deep root channels and add organic matter to soil; dood cropping practices will help in several ways in soil compaction issues; promote plant roots to grow through and break up compacted soil; increase soil organic matter; improve soil structure; improve water infiltration and penetration into the soil; and promote biological diversity. A biological healthy soil will be more resistant to soil compaction Minimizing the risk of Soil Compaction A number of management options can be implemented to minimize the risk of soil compaction. This include keeping a protective residue cover on the soil surface to reduce the negative effects of rain or irrigation water causing soil crusting, minimizing or eliminating soil tillage to prevent soil aggregate breakdown and induce the development of a tillage "hardown" this goal can be achieved by direct seeding and the elimination of soil cultivation and as far as possible, avoid field traffic when soil are wet. 4.2 Control There are four strategies commonly used in dealing with compaction: (a) avoidance (b) alleviation (c) controlled traffic and (d) acceptance (a) Avoidance: Avoidance is the most desirable where it is physically and economically possible. The old adage of "stay off the field until it's fit to work" still applies. However, the possible severe economic repercussions of delaying planting, harvesting or other operations may outweigh compaction demand or loss. While large, heavy machine is often blamed for soil compaction problems, it also offers opportunity to minimize compaction. Large capacity machinery means fewer wheel tracks across the field because of wider working width. If wheel track spacing can be standardized among different pieces of equipment, soil compaction problems can be minimized. (b) Alleviation: At times, potentially damaging compaction is unavoidable. What can be done about it? There are two ways of alleviating and lessening the damage caused by compaction. (I) attempt to remove the compaction (ii).attempt to reduce the adverse effects of the compaction One way to reduce the adverse effect of compaction is to apply fertilizer in a way that increases the availability. Such measures may include row/band application of phosphorus or potassium. Split application of nitrogen or other practices that minimize the loss of nitrogen by denitrification may also alleviate compaction problems. (c) Controlled traffic: In a normal year, as much as 90% of the field may be tracked by equipment. The philosophy behind controlled traffic is to restrict the amount of soil travelled on by using the same wheel tracks. Seventy to ninety percent of the total plough 186

6 Proceedings of the International Soil Tillage Research Organisation (ISTRO) Nigeria Symposium, Akure 2014 November 3-6, Akure, Nigeria (d) layer compaction occurs on the first trip across the field. By controlling traffic, the tracked area will have a slightly deeper compaction but the tracks will not be compacted. Acceptance: Acceptance is waiting for the detrimental effects to be removed by natural forces. However, this may not be practical if there is compaction below the plough layer. The deeper the compaction and higher the clay content, the longer it will persist. 5. Summary/ Conclusion The effects of compaction on plant growth and yield depend on the crop grown, soil type, and weather conditions. Under dry conditions, slight compaction is beneficial but too much is detrimental to yield. Under wet conditions, any amount of compaction can decrease yields as a result of N losses, reduced K availability, and inhibited root respiration due to reduced soil aeration. A moderate amount of compaction in the seed zone at planting is desirable in order to provide adequate seed-soil contact. Excessive compaction decreases water infiltration and storage, decreases root growth, reduces the soil volume explored by roots and can reduce crop yields. Depth of compaction increases as both the soil moisture content and axle load increases. Compaction in the plough layer is largely related to contact pressure of the tire. Compaction below the plough layer is related to total axle load. Surface compaction can usually be alleviated by moldboard or chisel ploughing. Subsoil compaction takes years to alleviate. References Bailey, A.C, Johnson, C.E, Schafer, R.L. (1986): A model for agricultural soil compaction. Vol.33 (4): Giles, J.F. (1980). Effects of compaction on soil conditions and crop growth.in: 1979 Sugar Beet Research and Extension Reports Giles, J.F. (1981). Effects of compaction on crop response IN:1981 sugar beet Research and Extension reports Jodi Dejong-Hughes.( 2001). Soil compaction-causes, effects and control. University of Minnesota West Central Research/Outreach centre. Jones, A.j., R.A Wiese, E.C Dickey. (1999). Management strategies to minimize and reduce soil compaction. University of Nebraska, G A Lewandowski, A.( 1999). Compaction-Soil Management Series 2 University of Minnesota Extension Service, BU-7400 Moncrieff, J.F., and E.E Schulte (1983).The effects of tillage on soil compaction and crop growth Soane, B.D., and C. van Ouwerkerk.( 1994). Soil Compaction in crop production. ISBN Chap12 pg Voorhees, W.B.(1986). The effect of compaction on crop yield. Proc. earthmoving industry Conf.Peoria, IL. April, 1986 Voorhees, W.B., W.W. Nelson, and G.W. Randall. (1986). Extent and persistence of sub-soil compaction caused by heavy axle loads. Soil Sci. Am J