Global Extent of Land Degradation and Its Human Dimension - Principles of Sustainable Soil Management in Agroecosystems - page 205

investment in prevention of land degradation or rehabilitation of degraded lands
is even more limited.
At the international community, there have been increased efforts recently to
address land degradation. The recent Rio +20 summit called for achieving zero land
degradation (UNCCD 2012). As part of efforts contribute to providing empirical evi-
dence for achieving zero net land degradation, this study analyzes land degradation
and its impact on human welfare. The study also discusses actions, which should be
taken to prevent land degradation and/or rehabilitate degraded lands. Given that land
degradation has a large impact on food security, the paper examines agricultural
productivity across regions and actions that could be taken to enhance food security
in developing countries experiencing hunger.
9.2 ANALYTICAL METHODS AND DATA
Consistent with other global studies on land degradation and improvement, we use
land cover data captured by satellite (Vitousek 1994; Morawitz et al. 2006). We note
its weaknesses as a degradation proxy (e.g., see Vlek et al. 2010). For example, river
basin scale studies in West Africa have shown that the biomass productivity [normal-
ized difference vegetation index (NDVI)]-based land degradation assessment may
underestimate the extent to which soil is being lost, unless a correction is included to
account for atmospheric fertilization (Le et al. 2012). Use of land cover change as an
indicator of land degradation or improvement is increasing since it is easy to capture
and that its cost continues to fall. We use change in the NDVI to represent land deg-
radation or improvement. We overlay the global land cover change with poverty in
order to understand the relationship between land degradation and poverty and draw
conclusions on their patterns across major regions. We then analyze the impact of
land degradation on food security. Finally, we examine the drivers of land degrada-
tion in order to draw policy and strategies for taking action against land degradation.
Details of the analysis of the impact of land degradation on crop productivity and
drivers of land degradation are given below.
9.2.1 I mpact of L and d egradatIon on f ood S ecurIty
We examine the impact of land degradation on yield of maize and rice, which
are major crops in the world. We first examine the yield gap—that is, the differ-
ence between potential yield and actual yield across major regions of the world—
and examine its relationship with land degradation. We then examine the impact
of unsustainable soil nutrient management on the yield of maize and rice in Mali
and Nigeria as case study countries. Selection of the two countries was based on
data availability. Previous work by Nkonya et al. (2011c,d) used a well-calibrated
crop simulation model to provide 30-year data showing the impact of crop residue,
manure, and nitrogenous fertilizer applications on maize and rice yield. Nkonya et al.
(2011c,d) used the Decision Support System for Agrotechnology Transfer (DSSAT)-
CENTURY (Gijsman et al. 2002) crop simulation model, which is more suitable for
simulating low-input cropping systems in SSA. The DSSAT-CENTURY model was
calibrated using soil, water, and weather data collected from the countries included