These data are from rich Highveld red soils, and the pattern will be different in the majority of sandy or sandy loam soils elsewhere, where loss of organic matter is often more sudden, and very difficult to reverse. Many soils in the communal areas where cultivation has been continuous for over a century are essentially silica based substrates, with little inherent fertility or organic matter and so very poor structure. This is farming as hydroponics, where water and nutrients must be held in the substrate for the period that plants need it. This requires careful soil water and nutrient conservation efforts, ones that are quite different to those needed in other, richer soils.
This highlights the contrast between ‘outfield’ crop farming (often on very poor, sandy soils) and ‘homefields’ or gardens, where soils are richer, and improved by organic matter additions and careful cultivation. These two systems are quite distinct, and managed separately with different levels of attention and inputs. Sociologically they are distinct too, with homefields and gardens often the domain of women, while outfields being farmed by men (although of course this is not universally the case). There are therefore often intrahousehold disputes over where valued inputs – labour, manure, compost, fertiliser – are placed, reflecting this gendered differentiation of farming.
The garden/homefield vs outfield distinction is important for designing interventions, as there are quite different priorities in each, both technically and socio-economically. This is often forgotten. The rise of ‘conservation agriculture’ as a panacea to Zimbabwe’s agricultural challenges has meant a massive focus on digging pits in fields, supported by numerous NGOs and development agencies. But too often the key distinction has not been acknowledged, and problems emerged. Conservation agriculture (pit digging, with focused application of feritliser) is a gardening technique and highly suitable for small areas – indeed versions of it have long been applied before the development agencies arrived. It makes sense to limit application, focus water and nutrients, and manage individual plants intensively when working in a garden (even I do it in my own allotment in Brighton). But when agencies try to get people to do it in a whole field over a large area it is not surprising that it doesn’t work, and is widely resented (‘dig and die’ is the local term). People may temporarily comply to get the inputs, or as part of social pressure, but in the long term such efforts are not going to have an impact. This is why a differentiated response is essential.
In next week’s blog I will discuss some of the lessons from the extensive scientific and technical work that has been carried out in Zimbabwe and elsewhere in Africa, and draw some implications for the design of interventions.