GET THE APP

Do You Think it is Time to Consider Legume-Based Cropping Systems
Journal of Pollution Effects & Control

Journal of Pollution Effects & Control
Open Access

ISSN: 2375-4397

+44 1223 790975

Editorial - (2014) Volume 2, Issue 1

Do You Think it is Time to Consider Legume-Based Cropping Systems Again?

Tek Maraseni*
Institute of Agriculture and Environment, University of Southern Queensland, Toowoomba,Queensland, Australia
*Corresponding Author: Tek Maraseni, Institute of Agriculture and Environment, University of Southern Queensland, Toowoomba, Queensland, Australia, Tel: 07-46312995 Email:

Agriculture is one of the major global sources of greenhouse gas (GHG) emissions; on-farm sources alone emit roughly 60% of all nitrous oxide and 50% of all methane emissions (WRI, 2012). Modern agriculture is more intensified, mechanised and modernised than ever before, and there are increasing demands for more fuel, electricity, farm machinery and agrochemicals. In addition, many associated off-farm operations require significant energy inputs, resulting in even more GHG emissions [1-12]. As a result, from 1990 to 2005, GHG emissions from agriculture increased by 14%, with average annual increase in emissions of 49 Mt CO2e/yr (US-EPA 2006). Significant reductions in farm inputs are needed to reduce farming costs and to curb increasing GHG emissions. Cropping systems that minimise farm input related costs and GHG emissions and also improve the sustainability of the soil system are the demand of this century.

In the past, legume-dependent cropping systems were very popular across the world and a key factor in maintaining nitrogen levels in the soil. With the invention of the Haber-Bosch process of synthesizing ammonia, the primary ingredient for producing synthetic N fertilizers, farmers around the world replaced legume rotations and other traditional sources of N fertility with synthetic N fertilizers during the 20th century [13]. The rapid adoption of synthetic N fertiliser is reflected in increasing global fertiliser consumption. In conjunction with the replacement of legume based N-fertiliser by synthetic N-fertiliser, the worldwide use of agricultural pesticides also increased rapidly [2].

Part of the applied N-fertiliser and biologically-fixed N emits into the atmosphere in the form of N2O, which has 298 times more global warming potential than CO2 [14]. As a result, N2O is responsible for an estimated 6% of observed global warming [15]. There is some debate within the scientific community about whether the biologically-fixed N emits as much GHG as N fertiliser. For example, Maraseni et al. [15] suggested that the N2O emissions from legume crops exceed those from N due to frequent wetting and drying cycles over a longer period, while [16] argued that the biologically-fixed N is ultimately derived from solar energy while N fertiliser requires significant amounts of fossil fuels, thus, legumes should be have a lower impact. Despite this, the IPCC has set the same emission factor of 1.25% NO2-N emissions per kg for both N-fertiliser and biologically fixed N.

Concern has also been expressed that the human population now exceeds the carrying capacity of agricultural systems that depend on legumes for N inputs [16,17] thus the complete avoidance of synthetic N fertiliser may be impossible, especially in densely populated countries with limited cultivatable land.

Despite these debates, in recent years, legume-based rotational cropping systems have become more popular for various reasons:

• N fertilizers have been linked to numerous environmental problems including marine eutrophication, global warming, groundwater contamination and stratospheric ozone destruction [15]

• Legumes can fix N and make N available to companion and/or subsequent crops thus reducing reliance on N-fertilisation and related costs and GHG emissions [6]

• Globally the price of N-fertiliser is escalating, and is expected to rise further with the global commitment to reduce energy consumption and GHG emissions; legumes offer a cheaper alternative;

• Legume-based rotations help to maintain pest populations and retard pest evolution [15] and therefore reduce pesticides application rates, related costs and GHG emissions;

• Legume-based rotations help to reduce weed seed banks [16] and therefore reduce herbicides application rates, related cost and GHG emissions;

• Under a global emissions reduction commitment, meat would be considerably more expensive and protein-rich legumes could provide a good substitute for animal protein;

• There is increasing recognition of the role of legumes in reducing cholesterol levels in the blood, reducing heart-disease risk and helping people with diabetes;

• N-fixing legumes can increase soil carbon levels [17] further improving the productivity, profitability and sustainability of soil systems, and help generate soil carbon credits if agriculture is included in the emission reduction targets;

• Some legumes have the capacity to prevent N leaching by producing nitrification inhibitors [18].

• Some legumes increase crops yield. For example, in Australia, the legume vetch increased cotton yield by ~18% when grown in rotation with cotton [19]. Cotton grown after vetch was better at taking up N, P, K, Zn and Cu [19]. Similarly, grain legumes in rotation with tropical crops improve the yield of cereals in tropical regions, and also reduce the incidence of wheat root rot which reduces wheat leaf disease and pests and

• Obtaining N from legumes is potentially more sustainable than from industrial sources [15].

Hence, exploring the potential of legume-based cropping systems, especially from a GHG emissions and environmental perspective is crucial. In particular, research comparing GHG emissions from soils and various on-and off-farm inputs between legume-based and N-fertiliser based monoculture, rotational and intercropping cropping systems is needed. This study should be essentially a life cycle analysis (LCA) of crops, estimating GHG emissions from seed to supermarkets. The specific objectives would include the estimation of GHG emissions from factors such as:

1. Flux of soil carbon;

2. Construction of buildings and building materials for specific purposes of the cropping industry;

3. Production and combustion of fossil fuels used for farm operations;

4. Production, packaging, storage and transportation of agrochemicals;

5. N2O from soils due to use of N-fertiliser and production of biologically fixed N;

6. Production and use of electricity for irrigation;

7. Production of farm machinery used in the cropping;

8. Production and use of electricity for crops processing (cleaning, drying, etc.);

9. Production and transportation of crops packaging;

10. Transportation of crops from farms (or storage) to domestic markets;

11. Use of cold storage and processing facilities; and

12. Decaying crops wastes.

References

  1. Crews TE, Peoples MB (2004) Legume versus fertiliser sources of nitrogen: ecological tradeoffs and human needs. Agriculture, Ecosystems and Environment 102: 279-97.
  2. CSIRO (2009) Vetch- the legume that increases cotton profits. CSIRO Plant Industry, CSIRO.
  3. Dalal R, Weijin W, Robertson GP, Parton WJ, Myer CM, et al. (2003) Emission sources of nitrous oxide from Australian agricultural and forest lands and mitigation options. Australian Journal of Soil Research 41: 165-195.
  4. Danga BO, Ouma JP, Wakindiki IIC, Bar-Tal A (2009) Legume wheat rotation effects on residual soil moisture, nitrogen and wheat yield in tropical regions. Advances in Agronomy 101: 315-349.
  5. IPCC (2007) Changes in atmospheric constituents and in radiative forcing.
  6. Liebman M, Dyck E (1993) Crop rotation and intercropping strategies for weed management. Ecological Application 3: 92-122.
  7. Maraseni TN, Cockfield G (2012) Including the costs of water and greenhouse gas emissions in a reassessment of the profitability of irrigation. Agricultural Water Management 103: 25-32.
  8. Maraseni TN, Mushtaq S, Reardon-Smith K (2012) Integrated analysis for a carbon- and water-constrained future: an assessment of drip irrigation in a lettuce production system in eastern Australia. Journal of Environmental Management 111: 220-226.
  9. Maraseni TN, Mushtaq S, Reardon-Smith K (2012) Climate change, water security and the need for integrated policy development: the case of on-farm infrastructure investment in the Australian irrigation sector. Environmental Research Letter 7: 1-12.
  10. Maraseni TN, Cockfield G (2011) Does the adoption of zero tillage reduce greenhouse gas emissions? An assessment for the grains industry in Australia. Agriculture Systems 104: 451-458.
  11. Maraseni TN, Cockfield G (2011) Crops, cows or timber? Including carbon values in land use choices. Agriculture, Ecosystems and Environment 140: 280-288.
  12. Maraseni TN, Cockfield G, Maroulis J (2010) An assessment of greenhouse gas emissions from the Australian vegetables industry. Journal of Environmental Science and Health Part B 45: 578-588.
  13. Maraseni TN, Cockfield G, Maroulis J (2010) An assessment of greenhouse gas emissions: Implications for the Australian cotton industry. Journal of Agricultural Science 148: 501-510.
  14. Maraseni TN, Mushtaq S, Maroulis J (2009) Greenhouse gas emissions from rice farming inputs: a cross country assessment. Journal of Agricultural Science 147: 117-126.
  15. Maraseni TN, Maroulis J, Cockfield G (2009) An analysis of Australia's Carbon Pollution Reduction Scheme. International Journal of Environmental Studies 66: 591-603.
  16. Maraseni TN, Cockfield G, Apan A (2007) A comparison of greenhouse gas emissions from inputs into farm enterprises in Southeast Queensland, Australia. Journal of Environmental Science and Health, Part A 42: 11-19.
  17. Paul K, Polglase P, Nyakuengama, JG, Khanna PK (2002) Change in soil carbon following afforestation. Forest Ecology and Management 168: 241-257.
  18. Smil V (2001) Enriching the earth. MIT press, Cambridge, Massachusetts.
  19. Vlek P, Rodriguez-khul G, Sommer R (2003) Energy use and CO2 production in tropical agriculture and means and strategies for reduction and mitigation. Environment Development and Sustainability 6: 213-233.
Citation: Maraseni T (2014) Do You Think it is Time to Consider Legume-Based Cropping Systems Again? J Pollut Eff Cont 2:e109

Copyright: © 2014 Maraseni T. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Top