Crop management strategies

Agricultural soils are a major cause of the increasing amounts of carbon we are seeing in the atmosphere.  This increase in atmospheric carbon levels has resulted from change in land use, land has been cleared on a huge scale to provide space for agriculture.  Therefore there has been a huge change to the species in the ecosystems and they have become less diverse leading to a reduction in carbon sequestration.  This post will discuss papers suggesting mitigation strategies aiming to increase and maintain carbon sequestration rates through varying crop management strategies.  

A paper by Freibauer et al (2004) which discusses economically viable potentials for increased carbon sequestration in soils in Europe.  They recommend the promotion of organic inputs on arable lands, introduction of perennials such as trees on arable land set aside for conservation and the promotion of organic farming. Similarly a paper by Lal (2003) suggests that effective ways of mitigating carbon loses are to use natural fertilisers such as manure and again plant perennials in marginal lands.  Lal also suggests that it is beneficial to diversify mono cultures and plant winter cover crops.  

Through planting perennials such as trees and other plants in marginal areas of crop lands it leads to a diversification of the land resulting in a higher carbon sequestration rate, as different species sequestrate different amounts of carbon, for example trees absorb much more than smaller plants due to their larger size.  Using natural fertilisers such as manure, are more beneficial than artificial fertilisers as not only do they maintain soil carbon levels more efficiently, they also improve the quality of the soil, leading to less degradation.  Planting winter cover crops can increase carbon sequestration because having plants present on fields for the majority year increases carbon intake into the soil rather than leaving fields bare where little carbon sequestration can take place.  

A paper by Vaccari et al (2011) suggested an alternative strategy, increasing soil carbon storage by using Biochar.  Biochar is a carbon rich product obtained through carbonisation of biomass and can be used for carbon sequestration.  Biochar is very resistant to decomposition, and there is some evidence that Biochar stores atmospheric carbon from centennial to millennial timescales.  They found most of these studies had been undertaken in tropical locations and there was a lack in temperate regions.  They undertook their study on durum wheat in Mediterranean climate conditions, and their results showed the viability of Biochar application to crops, showing positive effects of up to 30% on biomass production and yield, and it was successful for two consecutive seasons.  

In papers by Zhengchao et al (to be published 2013) and Alvarez (2005) it was shown that the use of fertilisers can increase soil carbon storage.  This occurs due to an increase in crop yield as a result of fertilisers, as there are more plants, more carbon is sequestrated. However, a major problem of using fertilisers to increase crop yield and consequently increase carbon storage in the soil, is that fertilisers result in higher nitrous oxide emissions.  Nitrous oxide emissions are becoming more prominent and I will discuss various mitigation strategies to reduce these in a following post.  Therefore using this strategy, the reduction of carbon dioxide in the atmosphere is offset by an increase in nitrous oxide.  

After reading papers on this topic, using Biochar seems a possible method, however, it is likely a wider range of research is necessary and that it would be more expensive for farmers to implement.  Whereas planting perennials in marginal areas, using natural fertilisers and planting winter cover crops seem to be the most efficient crop management strategies to improve soil carbon content.