Sorghum

Sorghum bicolor 2005, sep 4 by pethan Botanical Gardens Utrecht University

Sorghum bicolor at the Utrecht University Botanical Garden.

Sorghum (Sorghum bicolor [L.]Moench) is a complex species in the grasses family (Poaceae) with a wide variety of forms. Five main races of cultivated are commonly distinguished by their grain and spikelet morphology (Harlan and de Wet). The species also includes the wild progenitor subspecies, as well as weedy forms. The genus sorghum includes other tropical grasses, including the perennial diploid Sorghum propinquum (2n=2x=10) and the tetraploid perennial Sorghum halepense, commonly known as Johnson grass.

Sorghum was domesticated in Africa as an annual crop, is adapted to a wide range of growing conditions in terms of temperature, rainfall, soil fertility, altitude and latitude with a wide range of uses, such as many types of grain, animal fodder, firewood and construction material as well as biofuel. It is widely grown in arid, hot tropical regions, and can be highly photoperiod sensitive. It is a diploid (2n=20), partially autogamous crop. It’s genome was fully sequenced in 2009 (Paterson et al. 2009).

In some locations it is ratooned to produce two crops in the same year. Some early literature even suggests that sorghum was being used as a perennial grain in the early 20th century. Researchers at the Land Institute (Salina, KS) are currently breeding perennial varieties of grain sorghum and working with collaborators in Mali to test their performance there. Other research in the areas of bioenergy and livestock feeds have produced useful information on perennial sorghum for plant biomass production.

Mapping priority areas for perennial sorghum production

mali_mrg_maize_opt_srg

Map of optimal niche for perennial sorghum in Mali.

Researchers on the Perennial Grains for Africa project mapped optimal areas for perennial sorghum production using geographic data from Malawi, Mali, Ghana, and Tanzania. Perennial sorghum production is currently proposed as a strategy to be utilized on marginal agricultural lands that are poorly suited to the production of more dominant crops. Utilizing perennial sorghum on marginal areas could provide additional nutrition while not displacing a significant amount of current production.

First, marginal agricultural areas were identified by using a combination of map products that identified areas with a combination of marginal land suitability for agriculture, poor net primary productivity, and sub-optimal surface temperature and precipitation. These maps were then combined with maps that identified areas with optimal growing conditions for sorghum based on temperature and precipitation. The intersection of these two map products produces, then, a map of areas of that too marginal for the production of important staple crops, but have sufficiently good characteristics for the production of sorghum.

Evaluation of tradeoffs by smallholders

Researchers used choice experiments to study farmers’ preferences for attributes of a perennial sorghum crop. Choice experiments measure stated preferences of participants as opposed to revealed preferences that come from observed market transactions. Choice modeling is a method used to estimate the marginal value of various attributes of a good and is especially useful when an observed transaction of a good does not occur. Choice experiments are a flexible tool useful for understanding choices and demand for new products or technologies.

Choice experiments were conducted in three districts in regions in Mali where annual sorghum is cultivated under low, medium, and high rainfall: Sikasso, Koulikoro, and Segou. The sample consists of farmers from 318 village households that were interviewed in March 2015. Each respondent evaluated five choice scenarios in which different aspects of the proposed cropping system, such as labor requirements, seed requirements, forage production, soil improvement, and grain yield, varied.

These estimates were then used to calculate demand or willingness to pay by calculating the marginal rate of substitution between each attribute and the yield variable. These figures should be interpreted as percentages, since sorghum yield was expressed as a percentage in the choice experiments (eg. -60% to -20% reduction in yield). The most important attribute tradeoff was soil improvement, as farmers would accept approximately a 25% yield reduction if they knew the cropping choice was improving their soil. Other attributes were less important in choice experiments, but did differ between men and women. Women appeared to value forage quantity more than men, while men discount labor requirements of cropping systems more than women. These results indicate that reduced labor requirements of perennial systems may not be sufficiently important to motivate adoption, but improvements to soil are.

Modeling perennial sorghum adoption scenarios

To model the potential demand for perennial sorghum cropping systems as a replacement for annual sorghum in Mali, researchers developed system dynamics models that combine elements from sociological and economic theories of change that stress the importance of peer-to-peer communication in the adoption of new technologies. These models incorporated results from the choice experiments to further quantify farmers’ willingness to replace existing practices.

The primary control on adoption rates was related to the potential impact of sorghum on soil quality and subsequent productivity. A relatively modest 2% yield increase dramatically increases the adoption rate, whereas a 10% yield reduction significantly reduces it despite other potential benefits, such as reduced labor. Since the soil quality impacts are poorly understood in perennial sorghum currently, research on this subject will be very important in further clarifying adoption scenarios.

Sorghum_adoption_model

Adoption trajectories under minimum soil fertility benefits of perennial sorghum; 10% lower yields in perennial compared with annual sorghum; and 2% higher yields in perennial sorghum compared with annual.

Models were further extended to include greater climate variability, as is predicted by current climate change models for Mali. Year-to-year variability in yields introduced by climate change triggers disadoption, decreasing producers’ trust in perennial sorghum systems and ultimately decreasing adoption rates.

Bibliography on Sorghum