Fertilizer use intensification and manure use : the case of Tigrai, northern Ethiopia

There has been an increase in fertilizer use among farmers in the semi-arid Tigray region of Ethiopia during 2006-2015. Our household panel data covering nine years show that the average fertilizer adoption rate had increased from about 31% of plots in 2006 to almost 67% in 2015. Likewise, fertilizer use intensity increased from 28.6 kg/ha in 2006 to 88.5 kg/ha in 2015. Our study aims to explain the increase in fertilizer use and assess how it is associated with changes in manure use. This study is vital given the vast literature on low adoption and fertilizer use in Africa and the scanty literature on the relation between inorganic and organic fertilizers. We use panel data of farm household plots in three rounds (2006, 2010, and 2015) and estimate a correlated random effects double hurdle model with the control function approach to handle endogeneity. We analyze by splitting our sample by population density, market-access, and irrigation. The results show fertilizer use was higher in densely populated areas and areas with good market-access while its intensity was increasing in less densely populated areas, areas with good market-access, and non-irrigated plots. On the implication of increased uptake in fertilizer to manure use, our results suggest that the two inputs appear to be substitutes at the extensive margin. Moreover, with good market access, there seems to be complementarity between the two inputs at the extensive margin and substitution at the intensive margin.