Table 2 Explanatory variables and hypotheses.
Variable | Hypothesised effect on yield |
|---|---|
Main effects | |
Agricultural suitability (index on climate, soil, topography, i.e. natural coproduction factors) | + A higher agricultural suitability leads to higher yields |
Fertilizer use intensity (anthropogenic coproduction factor) | + Higher fertilizer use intensity leads to higher yields |
Manure use intensity (anthropogenic coproduction factor) | + A higher manure use intensity leads to higher yields |
Net capital stock intensity (anthropogenic coproduction factor) in 2014 US$ | + A higher proportion of net capital stock/area leads to higher yields due to more industrialised agriculture |
Interaction effects | |
Agricultural suitability:fertilizer use intensity | − A substitution effect, i.e. the higher fertilizer use intensity the lower the effect of suitability on yield |
Agricultural suitability:manure use intensity | − A substitution effect, i.e. the higher the amount of manure applied to soils the lower the effect of suitability on yield |
Agricultural suitability:net capital stock intensity | + / − An enhancement effect, i.e. the higher the amount of net capital stock, the more effective a country can make use of agricultural suitability for achieving higher yields (e.g., using machinery for less suitable soils); or a substitution effect |
