KEYNOTE ADDRESS. Tillage for Environmental Sustainability

Transcription

1 KEYNOTE ADDRESS 1. Introduction Tillage for Environmental Sustainability Engr. Professor John O. Ohu B.Sc. (Ife), M.Sc. (Cranfield) PhD (McGill) FNIAE, FNSE, FAEng, MISTRO, COREN Regd. (Soil and Water Engineering Consultant) Dept. of Agric & Environmental Resources Engineering University of Maiduguri Soil degradation, decrease in soil productivity owing to land misuse is a major threat to agricultural sustainability and environmental quality. This remains so because of high demographic pressure, shortage of prime agricultural land, harsh environmental condition and resource poor farmers who cannot afford science based recommended inputs (Lar, 1995). With continued population growth and increasing demand on water resources, conservation tillage will have an increasing role to play in farming during this millennium. It has been reported that world population is expected to be 8.5 and 9.0 billion by 2025 and 2050 respectively (Berry et al. 2003). The increase in crop yields to sustain this population shall be by effective cultivation of land that is currently under production, since most of the world arable land is already being cultivated. The term tillage used broadly, embraces all operations of seedbed preparations that optimize soil and environmental conditions for seed germination, seedling establishment and crop growth. Tillage includes mechanical methods based on conventional technologies of ploughing and harrowing, weed control using herbicides and fallowing with cover crops controlled by direct seeding through its residue mulch. Tillage influences upward movement of moisture to the soil surface, vapor transfer from the surface ton the atmosphere, heat transfer to the soil, provides an ideal opportunity to break up nutrients formed in the deep zones of the soil, and disrupts pests and pathogen cycles. Proper tillage can alleviate soil constraints while improper tillage leads to a number of degradation processes such as: damage to soil structure, accelerated erosion by wind and water, depletion of organic matter and of physical manipulation fertility, decreasing of water movements, organic carbon and plant nutrients in the soil. Generally, tillage is a process of physical manipulation of the soil to achieve weed control, finess of tilth, smoothness, aeration, artificial porosity, friability, optimum moisture content to facilitate sowing and covering of the seed. 1

2 2. Tillage 2.1 Benefits and Disadvantages of tillage Benefits of tillage Tillage softens the soil and prepares seedbed for placing seeds easily at suitable depth that will result in uniform germination of seeds. It is used to incorporate previous crop residues along with any soil amendment such as organic and inorganic fertilizers. Tillage helps to release soil nutrients needed for crop growth. It also helps in controlling several soil and residue borne diseases and pests through burial and soil disturbance. Tillage gives temporary relief from compaction by using implements that could shatter below ground compaction layers formed in the soil Disadvantages of Tillage Detrimental effects of tillage on both farmers and environment include: 1. Costs money in form of fuel for tractors, wear and tear on equipment and the operator. The annual costs of feeding and caring of animals used as power source is high. 2. Green house gas emissions from the burning of diesel add to global warming. 3. Soil organic matter is oxidized when exposed to air by tillage, hence decline of organic matter disrupts the pores left in the soil by roots and microbial activities. 4. Soil bare surface exposed after tillage is prone to break down aggregates as the energy from raindrops is dissipated resulting in clogging of soil pores, consequently reducing water infiltration. 5. Soil bare surface after tillage is prone to wind erosion. 6. Tractor wheels compact the soils below the surface. 2.2 Influence of tillage on soil loss by water and wind affecting the environment Tillage objective is to maintain the upper layer of the soil in an aggregate state for facilitating adequate aeration and water infiltration for crop development. However, most serious erosion usually occurs on soils that have been recently ploughed, disked or harrowed. Tillage erosion increases landscape heterogeneity through creation of distinct landforms and relatively rapid re-distribution of soils from upland positions to depressions. The net effect of soil erosion is an increase in field variability and a reduction on crop production potentials. Top soil loss by erosion often decreases nutrient supply and subsequently productivity because of unfavourable physical characteristics resulting from erosion could reduce infiltration, induce crusting or reduce the effective root zone. Other problems include increase in turbidity of runoff, which has adverse effect on quality of surface water, and sedimentation lowers available water storage. Severe erosion by water 2

3 could lead to gullies, stream and rivers, which could destroy or reduce size of farm lands, roads and even houses resulting in environmental problems. Runoff from agricultural lands may carry sediments, chemical fertilizers and pesticides, all of which degrade water quality and upset ecosystems of streams and lakes, reservoirs, rivers and pollution of surface and groundwater resulting in serious environmental problems. 2.3 Tillage practices for increased productivity and environmental sustainability The issue of sustainability and environmental quality will remain a major challenge to agriculture for generations. The performance indicators to use in assessing particular tillage practice suitability and its ability to preserve the resource base will depend on agronomic returns in terms of production per unit area or per unit time. It will also depend on agronomic returns in terms of production per unit area or per unit time that plays a vital role in maintaining soil s life support process such as organic matter content, per unit loss of soil effective rooting depth, per unit increament of major pollutants to streams or groundwater. Assessing the suitability of tillage methods in terms of the economics of crop production on a seasonal or annual basis alone is not enough. Appropriate system performance indicators to assess suitability as influenced by tillage methods and soil management are yet to be established. The holistic approach in many parts of the world is conservation tillage. This is an approach in which long-term sustainability, preservation of environment quality and resource base, are given priority over short-term economic returns. Conservation tillage is site specific and no single blue print of cultural practices is universally applicable. It includes notillage, ridge tillage, mulch tillage, strip tillage and reduced tillage. The appropriate type of conservation tillage, depends on both biophysical and socioeconomic factors and the interactions between them. Generally, soil degradation is a serious problem of agricultural soils. The main justification for conservation tillage is to prevent soil erosion, provide favourable soil and microclimate environments, reduce risk of environmental pollution, decrease risks of soil salinity and sodicity and enhance productivity of the soil. Conservation tillage is aimed at alleviating specific constraints such as; accelerated erosion, drought stress, surface sealing and crusting of subsoil compaction, unfavourable soil temperature regimes, anaerobic conditions in the root zone and other factors that are responsible for low soil fertility. The use of herbicides to control weeds in conservation tillage is generating a controversy. The herbicides used pollute natural waters. The transport system of herbicides in soils is not understood. Therefore, long-term, ecological, and oriented field experiments need be performed and development of alternative methods of weed control be given a high priority. 2.4 benefits of conservation tillage Some benefits of conservation tillage systems compared to intensive or conventional tillage systems include: 1. Reduction in draft power requirement. 2. Longer period available for planting. 3. Increased water infiltration. 4. Better soil moisture conservation 5.Reduced moisture evaporation 6. Less water runoff and soil erosion. 7. Increases in soil organic matter 8. Increases in nutrient 3

4 availability. 9. Greater biological pest control 10. Improved soil organic matter, soil structure and build up in soil fertility, less erosion and reduced land degradation11. Reduction in production costs. 12. Increased yields and productivity. 13. Decreased labour and energy inputs. 14. Increased availability of water for crop production 15. Improved soil quality. 16. The reduction of energy consumption and mechanical work means reducing the emissions of CO 2, CO and SO 2 gases which are major air pollutants. The 2010 world corn report stated among facts about conservation tillage includes: A corn producer in the United States saves at least 3.5 gallons of fuel per acre by reducing tillage. On a farm with 1000acres of cropland, these savings add up to 3,500 gallons of diesel fuel per year. No-till acres have increased 35 percent to 55 million acres of land cultivated. Conservation tillage reduced soil erosion one billion tons per year. Farmers save $3.5 billion in water treatment and waterway maintenance. Conservation tillage saves farmers 309 million gallons of fuel per year. Conservation tillage improves wildlife habitat. The different Conservation tillage practices discussed below include: No-tillage No-tillage system refers to a method of planting crops in previously unprepared soil by opening a narrow slot, trench, or band only of sufficient width to obtain proper seed coverage. In this system the soil is left undisturbed from harvest to planting except for nutrient injection. Planting or drilling is accomplished in a narrow seedbed with coulters, row cleaners, disk openers, in-row chisels or rotor-tillers. No other soil preparation is required, and herbicides are used for weed control. The soil remains covered by crop residues from previous cash crops or green manure cover crops and most of the crop residues remain undisturbed at the soil surface after seeding. No-tillage is synonymous with zero tillage, slot planting, eco-fallow, sod planting, chemical fallow and direct drilling. Here, all the crop residues are retained on the soil surface. This tillage system is suited to well-drained soils. The efforts of many interests have contributed to no-tillage technology. Equipment manufacturers, chemical companies, researchers, crop and soil consultants, agricultural engineers and others have made significant impacts. No-tillage is practiced on about 70 million hectares worldwide. Approximately 46% is practiced in Latin America, 37% in the United States and Canada, 13% in Australia and 3% in the rest of the world including Europe, Africa and Asia. Advantages of no-tillage include: 1. Fuel conservation- Up to 80% of fuel used to establish a crop is conserved by converting from tillage to no-tillage. 4

5 2. Time conservation- The one to three trips over a field with no-tillage (spraying, drilling and perhaps sub-soiling) results in a huge saving in time to establish a crop compared with the five to ten trips for tillage plus fallow periods during the tillage process. 3. Labour conservation-up to 60% fewer person-hours are used per hectare compared with tillage. 4. Increased soil organic matter- By leaving the previous crop residues on the soil surface to decay, soil organic matter near the surface is increased which in turn provides food for the soil microbes that are the builders of soil structure. 5. Preservation of soil structure- All tillage destroys natural soil structure while notillage minimizes structural breakdown and increases organic matter and humus to begin the rebuilding process. 6. Reduced pollution of waterways- The decreased runoff of water from soil and the chemicals it transports reduces pollution of streams and rivers. 7. Improved traficability- Untilled soils are capable of withstanding vehicle and animal traffic with less compaction and structural damage than tilled soils. 8. Lower costs- The total capital and/or operating costs of all machinery required to establish tillage crops are reduced by up to 50% when no-tillage substitutes for tillage Ridge tillage Ridge-tillage is a method of preparing the seedbed and planting on a preformed ridge. It is a form of conservation tillage that uses sweeps, disk openers, coulters or row cleaners to maintain permanent ridges on which row crops are grown. The ridges are usually 10 to 15 centimeters higher than the middle row. The soil for making the ridges is derived from the area between the rows. The practice is intended for the production of row crops like corn, soybeans, cotton, sorghum, and sunflower. After harvest, crop residue is left until planting time. To plant the next crop, the planter places the seed in the top of the ridge after pushing residue out of the way and slicing off the surface of the ridge top to expose moist soil. Often, a band of herbicide is applied to the ridge top during planting. With banded herbicide applications, two cultivations are generally used. Since ridge tillage relies on cultivation to control weeds and reform ridges, this system allows farmers to further reduce their dependence on herbicides, compared with either conventional tillage or no-tillage system. In this operation, the soil is left undisturbed from harvest to planting except for nutrient injection. This system helps in controlling soil erosion, improving drainage, early soil warming, reducing soil compaction and cutting the cost of seedbed preparation Strip tillage Strip tillage or zone tillage is a method of preparing a seedbed on a strip 2.5 to 30cms wide and 2.5 to 20cms deep. It is also referred to the practice of tilling a narrow strip of soil where the seed is sown into the strip of tilled soil but the soil between the sown rows remains undisturbed. Strip-tillage is a modified form of no-tillage and it incorporates subsoil shanks with fluted coulters and crumbling baskets and offers the combination of deep tillage. In this 5

6 system, a uniform seedbed is produced and difficulties associated with transplanting into established sod, as in no-tillage, are minimized Mulch tillage Mulch tillage is a tillage system in which a significant amount of crop residue is left on the soil surface to reduce wind and water erosion. In this operation the soil surface is disturbed with tools such as chisels, field cultivators, disks, and sweeps prior to planting. Weed control is in most cases accomplished with herbicides. Mulch is dead plant material such as dry grass, straw, maize stalks, corn stalks, dry leaves, banana leaves, sugar-cane trash and other crop residues that can be spread on a soil surface or placed around stems. Mulching creates a more favourable environment for the macro fauna, which modify the soil by creating pores, thereby increasing their capacity and the soil permeability (McKenzie and Dexter, 1993). Mulching and minimum tillage decreases soil erosion, soil crusting, and the rate of surface evaporation and soil surface temperatures by maintaining organic inputs on the soil surface. Mulching also has a moderating effect on the soil temperature and contributes considerably to the conservation of soil moisture, as compared to exposed soils. A layer of mulch: 1. Reduces the impact of rain drops, catches runoff water and improves rain water infiltration. 2. Reduces soil temperature and evaporation losses. 3. Suppresses weeds. 4. Provides organic matter and soil crop nutrients. 5. Creates a living and fertile soil environment for sustainable and productive farming. 6. Standing stubble reduces wind speed at ground level and reflects rather than absorbs heat Reduced tillage Tillage smoothes the soil surface and destroys natural soil aggregations and earthworm channels. Porosity and water infiltration decrease following most tillage operations. Plough pans may develop in many situations, particularly if soils are ploughed with heavy equipment or when the soil is wet. Tilled soils have much higher erosion rates than soils left covered with crop residue. Because of the problems associated with conventional tillage operations, acreage under reduced tillage systems is increasing worldwide. Tillage that leaves 15 to 30 percent of the soil surface covered with residue after planting or 500 to 1000 kg ha -1 of small grain residue equivalent throughout the critical wind erosion period is termed reduced tillage. The concept of reduced tillage has become of increased importance because of the necessity to reduce costs of machinery and labour to carry out cultivations in a timely way and to treat natural resources with care owing to concerns over the natural environment. 6

7 3. Conclusions Leaving crop residue as field cover and eliminating tillage trips, can help farmers protect the soil from water and wind erosion, conserve moisture, reduce nutrient runoff, improve wildlife habitat and limit output of labour, fuel and machinery. Conservation tillage results in better soil quality, increases soil organic matter and moisture holding capacity. Conservation tillage also reduces pesticides and fertilizer runoff. No-till planting is the most cost-effective practice to reduce tillage trips, protect and enhance the environment. References Baker, R.D. and Rouppet, B Conservation Farming in New Mexico. Cooperative Extension Service Circular 555. Las Cruses, New Mexico Carter, M.R A review of conservation tillage strategies for humid temperate regions. Soil Tillage & Res., 31: CTIC, Conservation Technology Information, CTIC Partners, 2004, no 1, p. 7. Derpsch, R The extent of Conservation Agriculture adoption worldwide: Implications and impact. Proceedings of the Third International Congress of Conservation Agriculture. Nairobi, Kenya. Food and Agriculture Organization of the United Nations (FAO), Piloting conservation agriculture and improved land management. Available at IAC, Campinas, Brazil Grisso, R.D. Yasin, M. and Kocher, M.F Tillage implement forces operating in silty clay loam. Trans. ASAE, 39(6): Joseph K. Berry, Jorge A. Delgado, Rajiv Khosla and Fran Pierce, Precision conservation for environmental sustainability. Final Draft for Publication in the J. of Soil Water Conservation. Lal, R Tillage Systems in the Tropics: Management and Options and Sustainability. Food and Agricultural Organizations of the United Nations. 206pp. McKenzie, B.M., Dexter, A.R Size and orientation of burrows made by the earthworms Apporrectodea rosea and A. caliginosa. Geoderma, 56: Rolf Derpsch (2003). Conservation Agriculture and No-tillage Consultant, Paraguay Congress on Conservation Agriculture. World of Congress Report (2003). Environment-conservation, sustainability. Voorhees, W.B. (1992). Wheel-induced soil physical limitations to root growth. Advanced Soil Science, 19:

8 Table 1. Countries and area under no-tillage Country Area under no-tillage in ha 2001/2002 USA 22,410, 000 Brazil 17,356, 000 Argentina 13,000,000 Australia 9,000,000 Canada 4,080,000 Paraguay 1,300,000 Bolivia 417,000 North India, 350,000 Pakistan South Africa 300,000 Venezuela 150,000 Chile 130,000 Colombia 70,000 Uruguay 50,000 Mexico 50,000 Ghana 45,000 Others 1,500,000 Total 70, 208,000 Source: Rolf Derpsch, Conservation Agriculture and No-tillage Consultant, Paraguay, Congress on Conservation Agriculture Fig. 1: No-tillage cropping 8

9 Fig. 2: Example of ridge-tillage in Mexico (Baker and Rouppet, 1996). Fig. 3. Strip-tillage in Mexico (Baker and Rouppet, 1996) Fig. 4. Mulch tillage/stubble tillage Reduced tillage 9

10 Fig. 5: Reduced-tillage 10