Conservation agriculture adapts to and mitigates against climate change
Authors: Ranjan Bhattacharyya, Vinod Kumar Sharma, Mandira Barman* Sarvendra Kumar and Kapil Atmaram Chobhe
*Corresponding author E-mail: mandira.ssaciari@gmail.com


Conservation agriculture (CA) has been proposed as a widely adapted set of management principles that can assure higher sustainable agricultural production. Conservation agriculture offers an opportunity for arresting and reversing the downward spiral of soil degradation, opportunity to decreasing cultivation costs and making agriculture more input-use efficient, competitive and sustainable. Conservation agricultural systems sequester carbon from the atmosphere - while promoting a healthy environment, improve biodiversity and enhance natural biological processes above and below the ground (FAO, 2011). Hence, CA builds ecological foundation for agriculture. It is a way of farming that conserves, improves and ensures efficient use of natural resources. It is a concept for resource-saving agricultural crop production that strives to achieve acceptable profits together with high and sustained production levels while concurrently conserving the environment (FAO, 2011). Conservation agriculture has three key interlinked principles that can be applied in a variety of combinations to meet farmers' need. These are: (i) continuous minimal mechanical soil disturbance, (ii) permanent organic soil cover and (iii) diversified crop rotations of annual crops and plant associations of perennial crops (FAO, 2011). Conservation agriculture stops and reverses land degradation, boosts productivity and increase food security.


Impact of different components of conservation agriculture

Overall guiding principles for productive and sustainable cropping with conservation agriculture are summarised in table 1. The impacts of the three components of CA are discussed below:

a. Zero tillage: The beneficial effects are:
(i) Leaving the crop residues in the field on soil surface and regulation of grazing in conjunction with ZT reduce/prevent soil erosion;
(ii) Reducing runoff water, thereby increasing the rainwater harvesting;
(iii) Reducing the impact of high temperature on soil surface, i.e. prevented the negative impact of heat on seed germination;
(iv) Reducing fuel and mechanization usage, thus reduces C emission through less fossil fuel burning
(v) Restoring the bio-life in soil surface, such as earthworms, arthropods, and other insects which increases the depth of root layer and improves the organic matter and
(vi) Reducing organic matter decomposition that leads to increased soil organic carbon (SOC).

b. Residue retention: The good effects of soil cover are:
(i) Improved infiltration and retention of soil moisture resulting in less severe, less prolonged crop water stress and increased availability of plant nutrients;
(ii) Reduces evaporation, so conserves moisture for the crops;
(iii) Source of food and habitat for diverse soil life: creation of channels for air and water, biological tillage and substrate for improved biological activity through the recycling of organic matter and plant nutrients;
(iv) Increased humus formation and carbon accumulation;
(vi) Mitigation of temperature variations on and within the soils; and
(vii) Suppresses weed growth and creates better conditions for root development and seedling growth.

c. Crop rotation: The effects of crop rotation are:
(i) Higher diversity in plant production
(ii) Increased formation of soil aggregates and humus, leading to improved soil structure and C and N sequestration;
(iii) Better distribution of water and nutrients through the soil profile
(iv) Increased nitrogen fixation through certain plant-soil biota symbionts replenishes soil fertility, and improved balance of N/P/K from both organic and mineral sources and
(v) Reduction and reduced risk of pest and weed infestations and risk of the total crop failure.

Table 1. Guiding principles for productive and sustainable cropping with conservation agriculture (Adapted from ICARDA, 2012)

S. No. Do’s and Don’t do’s Explanation
1. Do not cultivate fields Plowing is unnecessary, takes time and money, and robs soil of moisture and structure
2. Do not burn stubble from the previous crop Retain as much of it and other residue as possible on surface of the soil
3. Allow livestock to graze on stubble This does not negate the many benefits of conservation tillage. Many countries have successfully integrated livestock into the system
4. Sow seed and fertilizer using a conservation agriculture seeder It allows planting through surface residue into narrow slits in the soil
5. When the rains are late, consider early dry-sowing It saves time and utilizes the first rain
6. Control weeds before sowing A glyphosate-based herbicide may be used, but this is often unnecessary where there is little summer rain.
7. New approaches may be needed to manage soil fertility and control pests, diseases and weeds Different location specific ways may be adopted to those in conventional systems
8. Manage major soil problems according to best practice to optimize yields To address the problems such as hard pan, acidity and salinity
9. Use crop rotations to break the cycle of cereal pests and diseases, and to better utilize soil nutrients and enrich them. Effective rotations are cereals with legumes, brassicas, other crops and forages


Conservation agriculture is not conservation tillage

Conservation tillage is a widely-used terminology to denote soil management systems that result in at least 30% of the soil surface being covered with crop residues after seeding ofthe subsequent crop (Jarecki and Lal, 2003). Zero tillage technology proved better for rabi season crops, especially wheat, gram, mustard and lentil. Wheat sowing after rice can be advanced by 7-10 days by adopting this technique compared to conventionally cultivated wheat, and wheat yield losses caused by late sowing can be avoided.

Conservation agriculture, on the other hand, is more than a zero-tillage-based cropping system. Farmers following the CA principles use low-cost tools and equipment and traditional crop varieties without herbicides or herbicide-tolerant varieties. Despite the promising effects of no-till in certain contexts (that is, rainfed agroecosystems), Pittelkow et al. (2014) observed that benefits in yield are only seen when the other two CA principles are also implemented. Of far greater concern is that conservation tillage alone tends to have the opposite of the intended goal, thereby placing farmers at increased risk of yield losses (Bhattacharyya et al., 2009), despite improvement in soil quality parameters due to a number of factors, including weed infestation and surface compaction.


Impact of conservation agriculture on environmental quality

Overall benefits of conservation agriculture is summarised in table 2. A system of continuous macropores is established under zero tillage, facilitating water infiltration and aeration of the soil as well as root penetration into deeper zones. Tillage mixes air into the soil which leads to a mineralization (oxidation) of the soil organic matter. In absence of soil tillage this mineralization is reduced. Adoption of conservation agriculture systems with crop residue retention may result initially in N immobilization. However, rather than reducing N availability, CA may stimulate a gradual release of N in the long run and can reduce the susceptibility to leaching or denitrification when no growing crop is able to take advantage of the nutrients at the time of their release.

Conservation agriculture increases availability of nutrients near the soil surface where crop roots proliferate. Slower decomposition of surface placed residues prevents rapid leaching of nutrients through the soil profile. The response of soil chemical fertility to tillage is site-specific and depends on soil type, cropping systems, climate, fertilizer application and management practices. However, in general nutrient availability is related to the effects of CA on SOC contents.

Table 2. Benefits of conservation agriculture
Economic benefits Agronomic benefits Environmental benefits Benefits to society
ü Time saving and thus reduction in labour requirement. ü Reduction of costs, e.g. fuel, machinery operating costs and labour cost. ü Higher efficiency ü Organic matter increase ü Soil water conservation ü Improvement of soil structure ü Yield stability ü Greater resilience to drought ü Reduction in soil erosion ü Improvement of water quality ü Biodiversity increase. ü Carbon sequestration. ü Favourable hydrologic balance to withstand extreme weather events ü Reduced deforestation ü More reliable and cleaner water supplies ü Less flooding due to better water retention and slower runoff ü Improved air quality with less wind erosion


Soil macro and micro fauna and flora is re-established resulting in better soil fertility. The different taxonomic meso-fauna groups respond differently to tillage disturbance and changed residue management strategies. However, in general tillage, through direct physical disruption as well as habitat destruction, strongly reduces macro-fauna including both litter transformers and ecosystem engineers. When reduced tillage is combined with residue retained on the soil surface, this provides residue-borne pathogens and beneficial soil micro-flora species with substrates for growth, and pathogens are at the soil surface, where spore release may occur. This can induce major shifts in disease pressure in CA. However, in general, CA also results in an increased functional and species diversity. Functional diversity and redundancy which refers to a reserve pool of quiescent organisms or a community with vast inter-specific overlaps and trait plasticity, are signs of increased soil health, and allow an ecosystem to maintain a stable soil function. Larger microbial biomass and greater microbial activity under CA can result in soils exhibiting suppression towards soil-borne pathogens and increased possibilities of integrated pest control are created. In south Asia, the adoption of zero tillage approach in an area of 5 million hectares saved an amount of 5 billion cubic meters of water annually. Such an amount may fill a lake of 10 km long, 5 km wide and 100 m deep. What is more, the amount of saved diesel would be about half a billion liters annually. This means an annual reduction of CO2 emission of about 1.3 million tonnes.

Conservation agriculture-based farming systems appear to be the best available option for sustainable agriculture, climate change mitigation and rural development. It also enhances ecosystem functions. Conservation agricultural methods can improve the efficiency of inputs, increase farm income, improve or sustain crop yields, and protect and revitalize soil, biodiversity and the natural resource base. It achieves to a high degree environmental sustainability of farming and provides many benefits to the non-farming rural population. Thus, adoption of location-specific conservation agricultural practices is proposed to be the need of the hour.

References
. Bhattacharyya, R., Ved-Prakash, Kundu, S., Srivastva, A.K., and Gupta, H.S. (2009) Soil aggregation and organic matter in a sandy clay loam soil of the Indian Himalayas under different tillage and crop regimes. Agriculture, Ecosystem & Environment, 132, 126-134.
2. FAO (2011) Soil carbon sequestration in conservation agriculture. In: Conservation Agriculture Carbon Offset Consultation - West Lafayette, Indiana, USA, 28-30 October 2008; United Nations Food and Agriculture Organization (www.fao.org) and Conservation Technology Information Center (www.conservationinformation.org) http://www.fao.org/ag/ca/doc/ca_ssc_overview.pdf ; Accessed on13/09/2015.
3. ICARDA (2012) Conservation agriculture: opportunities for intensified farming and environmental conservation in dry areas. International Center for Agricultural Research in Dry Ares (ICARDA) Research to Action 2, ftp://ftp.fao.org/ag/agp/ca/CA_CoP_May12/Conservation_agriculture_ICARDA.pdf; Accessed on 27/09/2015.
4. Jarecki, M.K. and Lal, R. (2003) Crop management for soil carbon sequestration. Critical Reviews in Plant Sciences 22, 471-502.
5. Pittelkow, C.M., Xinqiang L., Linquist, B.A., van Groenigen, K.J., Lee, J., Lundy, M.E., van Gestel, M., Six, J., Venterea, R.T. and van Kessel, C. (2015) Productivity limits and potentials of the principles of conservation agriculture. Nature 517, 365-370.




About Author / Additional Info:
Dr. Mandira Barman is a Scientist in the Division of Soil Science and Agricultural Chemistry, ICAR-Indian Agricultural Research Institute (ICAR-IARI), New Delhi, India since 2012. Her area of research interest is chemistry of micro nutrients in soils in relation to their availability to plants and nanotechnological applications to enhance nutrient use efficiency. Dr. Mandira has completed her Ph.D. on nickel nutrition of plant from ICAR-IARI, New Delhi.