John McDonagh

Estimates of the residual nitrogen benefit of groundnut to maize in Northeast Thailand

Four cultivars of groundnut were grown in upland soil in Northeast Thailand to study the residual benefit of the stover to a subsequent maize crop. An N-balance estimate of the total residual N in the maize supplied by the groundnut was made. In addition three independent estimates were made of the residual benefits to maize when the groundnut stover was returned to the land and incorporated. The first estimate (Estimate 1) was an N-balance estimate. A dual labelling approach was used where 15N-labelled stover was added to unlabelled microplots (Estimate 2) or unlabelled stover was added to 15N-labelled soil microplots (Estimate 3). The nodulating groundnut cultivars fixed between 59–64% of their nitrogen (as estimated by the 15N isotope dilution method using non-nodulating groundnut as a non-fixing reference) producing between 100 and 130 kg N ha-1 in their stover. Although the following maize crop suffered from drought stress, maize grain N and dry weights were up to 80% and 65% greater respectively in the plots where the stover was returned as compared with the plots where the stover was removed. These benefits were comparable with applications of 75 kg N ha-1 nitrogen in the form of urea. The total residual N estimates of the contribution of the nodulated groundnut to the maize ranged from 16.4–27.5 kg N ha-1. Estimates of the residual N supplied by the stover and fallen leaves ranged from 11.9–21.3 kg N ha-1 using the N-balance method (Estimate 1), from 6.3–9.6 kg N ha-1 with the labelled stover method (Estimate 2) and from 0–11.4 kg N ha-1 with the labelled soil method. There was closest agreement between the two 15N based estimates suggesting that ‘apparent added nitrogen interactions’ in these soils may not be important and that N balance estimates can overestimate the residual N in crops following legumes, even in very poor soils. This work also indicates the considerable ability of local groundnut cultivars to fix atmospheric nitrogen and the potential benefits from returning and incorporating legume residues to the soil in the upland cropping systems of Northeast Thailand. The applicability of the 15N methodology used here and possible reasons for the discrepancies between estimates 1, 2 and 3 are discussed.

From rhetoric to reality: farmer perspectives on the economic potential of biochar in China

Biochar has garnered much attention for its potential to improve farming productivity and sustainability by amending soil, enhancing crop yields, improving fertilizer use efficiency and sequestering carbon. However, few publications consider farmer perspectives on whether biochar is attractive as an agricultural input. This paper therefore investigates the micro-economics and social suitability of biochar in four contrasting Chinese agricultural systems, using linear optimization models and qualitative contextual data. Results demonstrate that commercially produced biochar is uneconomic as an independent farming input, whilst farm-produced biochar shows promise in just one of four case-study sites. This suggests that biochar research in China should shift away from on-farm production and application of pure biochar, towards combined biochar-inorganic fertilizer products.

Carbon benefits of wolfberry plantation on secondary saline land in Jingtai oasis, Gansu:A case study on application of the CBP model

The largest global source of anthropogenic CO2 emissions comes from the burning of fossil fuel and approximately 30% of total net emissions come from land use and land use change. Forestation and reforestation are regarded worldwide as effective options of sequestering carbon to mitigate climate change with relatively low costs compared with industrial greenhouse gas (GHG) emission reduction efforts. Cash trees with a steady augmentation in size are recognized as a multiple-beneficial solution to climate change in China. The reporting of C changes and GHG emissions for sustainable land management (SLM) practices such as afforestation is required for a variety of reasons, such as devising land management options and making policy. The Carbon Benefit Project (CBP) Simple Assessment Tool was employed to estimate changes in soil organic carbon (SOC) stocks and GHG emissions for wolfberry (Lycium barbarum L.) planting on secondary salinized land over a 10 year period (2004-2014) in the Jingtai oasis in Gansu with salinized barren land as baseline scenario. Results show that wolfberry plantation, an intensively managed ecosystem, served as a carbon sink with a large potential for climate change mitigation, a restorative practice for saline land and income stream generator for farmers in soil salinized regions in Gansu province. However, an increase in wolfberry production, driven by economic demands, would bring environmental pressures associated with the use of N fertilizer and irrigation. With an understanding of all of the components of an ecosystem and their interconnections using the Drivers-Pressures-State-Impact-Response (DPSIR) framework there comes a need for strategies to respond to them such as capacity building, judicious irrigation and institutional strengthening. Cost benefit analysis (CBA) suggests that wolfberry cultivation was economically profitable and socially beneficial and thus well-accepted locally in the context of carbon sequestration. This study has important implications for Gansu as it helps to understand the role cash trees can play in carbon emission reductions. Such information is necessary in devising management options for sustainable land management (SLM).

Land Management Strategies and their Implications for Mazahua Farmers’ Livelihoods in the Highlands of Central Mexico

Abstract This paper presents a case study from a Mazahua indigenous community in the rural Highlands of Central Mexico. It analyses Mazahua farming livelihoods characterised by subsistence agriculture, marginality, poverty and severe land degradation. Mazahua farmers face constrained environmental, socioeconomic and cultural conditions, which influence their local decisions on natural resource management. The results describe the capital assets base used, where land, livestock and crop production are imperative assets to support farmers’ livelihood strategies. It analyses local management practices to achieve livelihood outcomes in the short/long term, and to improve or undermine land characteristics and other related assets. It also presents a farmer typology constructed by local perceptions, a controversial element to drive sustainable development strategies at the local level. Finally, it discusses how local land management practices are adopted and their importance in developing alternatives to encourage positive trade-offs between conservation and production in order to improve rural livelihoods.