Systems thinking

crop loss systems framework
Figure 1. L, Labour; W, Water; F, Fertilizer; P, Pesticides; V, varieties & germplasm; T, Technology CP, Crop Profile; Ya, Attainable, Yield; IP, Injury Profile; YL, Yield Loss.

By Neil McRoberts, Laetitia Willocquet, Paul Esker, and Serge Savary

As we have noted before, it’s all too easy to assume that the basic work of understanding how plant pathogens and other pest organisms reduce crop yields, cause crop and post-harvest losses is already done.  It seems such simple science, and the information gained from it so basic to our understanding of the productivity of global food supply, that it is easy to see why most people would assume it’s an issue that agricultural research would have taken care of long ago.  In one sense it has, but it is also the case that much of the basic information about crop losses, globally, remains imprecise, or in many cases simply unavailable.  At the same time, while investment in research to understand detailed biological mechanisms of plant – pathogen interactions continues to be impressive, the simple but crucial field research to quantify losses and relate them to the intensity of attack from multiple pest organisms is relatively poorly resourced.  This is important because we now understand that pest complexes, and their associated injury profiles

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are much more closely linked to yield loss than individual pests or diseases. Furthermore, injury profiles are strongly influenced by cropping profiles, themselves the product of complex interactions between the local environment in which agriculture sits, and (importantly) the human choices concerning use of a key set of resources. Figure 1 shows a distillation of these concepts.

Central Uganda
Village smallholdings in central Uganda; food production and cash cropping exist in a complex mosaic of hundreds of individual holdings typically of an acre or less, with a few larger farms interspersed

On the left of Figure 1, six key resources for agriculture are identified; labour, water, fertilizer, pesticides, plant varieties, and a general category for technology.  These represent the human choices that combine to specify a given cropping profile –  the basic “character” of each crop production situation that defines both the manner in which it produces crops and the level of productivity it has (it’s attainable yield, Ya), and also (as we are increasingly learning) to characteristic profile of yield losses it will suffer.  Together, the attainable yield and the injury profile of a cropping profile, determine the yield losses it will routinely experience, and thus the extent to which it will, or will not, meet the food production needs of its dependent human population, and the extent to which it will use resources in an efficient way to achieve its productivity. The challenge we face is to understand the complex interactions that determine attainable yields and yield losses and translate these into tactical and strategic recommendations at a range of scales to improve the sustainability of food supply.