No debate about energy saving. Zero tillage/minimum tillage helps in carbon sequestration. However, weeds become serious pests sometimes. Adoption of this practice is existed in low lying areas where farmers just clean weeds and transplant rice seedlings. Moreover, soil texture and nature of crops dictates such practices.

Agreed Dr Biswas, short- and long-term effects of zero tillage on soil environment, inputs use efficiency etc are the concerns, regards

Dear Sir,

Tillage is defined as the mechanical manipulation of the soil for the purpose of crop production affecting significantly the soil characteristics such as soil water conservation, soil temperature, infiltration and evapotranspiration processes.

Zero tillage has been successfully practised in No of countries for several decades, with regular annual growth in the total area.  There has been an impressive rate of adoption and accelerating growth over the past two decades.

This suggests that tillage exerts impact on the soil purposely to produce crop and consequently affects the environment. As world population is increasing so the demand for food is increasing and as such the need to open more lands for crop production arises. The yearning for yield increases to meet growing demand must be done in a way that soil degradation is minimal and the soil is prepared to serve as a sink rather than a source of atmospheric pollutants. The principle of conservation tillage involves maintenance of surface soil cover through retention of crop residues achievable by practicing zero tillage and minimal mechanical soil disturbance. Retention of crop residue protects the soil from direct impact of raindrops and sunlight while the minimal soil disturbance enhances soil biological activities as well as soil air and water movement. The aim of this review, therefore, was to examine the effects of conservation tillage on soil, crop and the net effect on the environment. This may provide farmers and other land users the information on the desirability of a conservation tillage system for sustainable crop yield increases with minimal negative impact on the soil and the environment.

Types of conservation tillage

Conservation tillage practices range from zero tillage (No-till), reduced (minimum) tillage, mulch tillage, ridge tillage to contour tillage. No tillage (NT) involves land cultivation with little or no soil surface disturbance, the only disturbance being during planting while minimum tillage means reduced level of soil manipulation involving ploughing using primary tillage implements. In mulch tillage, the soil is prepared or tilled in such a way that the plant residues or other materials are left to cover the surface to a maximum extent. Ridge tillage involves planting crops in rows either along both sides or on top of the ridges which are prepared at the commencement of the cropping season. When tillage is at right angles to the direction of the slope it is referred to as contour tillage.

 1.       When ploughed, the residues are incorporated in the soil together with air and come into contact with many micro-organisms, which accelerates the carbon cycle. The decomposition is faster, resulting in the formation of less stable humus and an increased liberation of CO2 to the atmosphere, and thus a reduction in organic matter.

2.       The residues on the soil surface slow the carbon cycle because they are exposed to fewer micro-organisms and thus wane more slowly, resulting in the production of humus (which is more stable), and liberating less CO2 to the atmosphere.

In terms of short-term organic matter loss, the more a soil is tilled, the more the organic matter is broken down attached table. There are also longer-term losses, attributed to repeated, annual cultivation. Cropping systems that return little residue to the soil accelerates this decline. Many modern cropping systems combine frequent tillage with small amounts of residue, with resultant reductions in the organic matter content of many soils. Historically, manure application (from farm livestock) was common, and it was a dynamic way of maintaining organic matter levels despite repeated cultivation and low residue returns to the soil. Increased on-farm mechanization has reduced livestock numbers, so this source of organic material has been reduced considerably.

Organic matter production and conservation is affected dramatically by conventional tillage, which not only decreases soil organic matter but also increases the potential for erosion by wind and water (Plate 8). The impact occurs in many ways:

1.       Ploughing leaves no residues on the soil surface to lessen the impact of rain.

2.       Ploughing reduces the quantity of food sources for earthworms and disturbs their burrows and living space, hence populations of certain species decrease drastically. Moreover, reduction of earthworm numbers reduces their impact, through burrowing, in increasing porosity and aeration (particularly continuous macropores) and lowers their ability to bury and incorporate plant residues, which facilitates rapid decomposition of organic matter.

3.       Tillage by repeated hoeing or discing smoothes the surface and destroys natural soil aggregates and channels that connect the surface with the subsoil, leaving the soil susceptible to erosion. Old root channels and earthworm holes are eliminated, as are the cracks between natural aggregates. The large pores, the ones destroyed by conventional tillage practices, are necessary to conduct water into the soil during rainfall.

4.       The development of a plough pan or hoe pan, a layer of compacted soil resulting from smearing action at the bottom of the plough or hoe, may retard both root penetration and water infiltration.

5.       Ploughing or discing under dry conditions exacerbates the pulverization of the soil, causing the soil surface to crust more easily, leading to greater water runoff and erosion. This is exacerbated by reduced soil surface roughness, which leaves few depressions for temporary storage of water during intense storms.

6.       Increased runoff during rainstorms may also increase the possibility of drought stress later in the season, because water that runs off the field does not infiltrate into the soil to remain available to plants.

On almost all cultivated land, soil tillage for crop production, often with heavy disk ploughs followed by disk harrowing, resulted in many problems. These included:

1.       Loss of the porous organic covering of the forest floor where land had been cleared.

2.       Pulverization of surface soil together with compaction of the sub tillage layer.

3.       loss of organic matter from the upper soil layers by rapid oxidation from the exposed surface;

4.       loss of potential soil moisture as runoff;

5.       Reduction in soil depth by erosion of topsoil, resulting in losses of seeds and fertilizers, and causing additional replanting costs.

6.       Declining flow and drying-up of streams and rivers during dry seasons.

Please find attached herewith realtated articles,

Regards,

Prem Baboo

Interesting question Naveen . Tillage and crop residue  incorporation are the two most driving factors for the success of conservation agriculture. On the contrary,  residue retention and reduced tillage are both conservation agricultural practices , may enhance the stabilization of SOC in tropical soils. Tillage disturbance  is the dominant factor reducing SOC stabilization in clay soils , especially it reduces SOC in micro-aggregates . Therefore , sustainability of conservation agriculture should prioritize the maintenance of carbon inputs ( For example, residue retention ) in coarse textures soils , but should focus on reduction of SOC decomposition ( For  example , reduced tillage) in fine textured soils. Enclosed below an interesting PDF for further reading .

thanks, anoop for a relevant article to this topic, as well your comments are practical principles of tillage and residue management

regards 

lot of field/multi-locational experiments carried out in the recent past on this aspect, perfect quantification needed for short- and long-term consequences into generation of transfer functions, which subsequently can be used in sub-routine development for fit into crop simulation models for applications

regards

CA, Zero tillage have been widely debated for positive as well negative platform, suitability under different soil textures/production environments, need to consolidate their short-  and long term benefits/ill effects too.

need to translate in soil process models to be used for regional applictions as well agro-advisories

thanks abhishek for nice article CA-FAO

Regards

Good enough, all beneficial aspects highlighted, probably other side has not been looked into, weed infection, insects population, subsoil compaction and its after effects on crops particularly in low organic matter soils, clay soils and irrigated areas where canal water is used which also leaves fine soil particles and seals the surface and sub-soil making compaction further advance.

What fayyaz says is right

So long as performing zero tillage in maize-wheat or rice wheat crop sequence along with retention of crop residues of previous crop, following three problems are faced:

1. weed infestation : the weed seed existing in upper 3 to 4 cm soil depth emerge simultaniously with germinating crop seed as soon as they get suitable germination condition. the only rather essential way to counter this problem is chemical method of weed control as manual weeding isnot only costly but also labourers are not available at peak period of weeding.

2. Rodents problem: As under zero tillage land remain undesturbed owing to no ploughing, the rats stay comfortably under soil and damage crop sown, reducing crop yield substantially.

3. Heavy pressure of pathogens: Retention of crop residues invites lot of insect and disease pathogens which survive on crop residues. The moment we sow a crop seed, the soil borm insect like cut worm in maize, feed upon the seeds thus the germination percentage is drastically reduced. The best way to get rid of is seed treatment with chlorpyriphos @10ml in one litre water gives enhanced crop seed germination.