There is general agreement that more crop biomass will need to be produced both to feed the growing human population and to facilitate the transition from our fossil-based economy to a bio-based economy. Knowledge of crop production and required inputs is fundamental to support these developments.
Based on a methodology that uses soil and climate information as basic input for a crop growth simulation model (Report: Agricultural resource scarcity and distribution: a case study of crop production in Africa), we have calculated global production possibilities of tropical maize and spring wheat (under rainfed and irrigated conditions; simulation of other crops, including some perennials, is also possible). The analyses take agro-ecological principles as basis which safeguards production estimates to remain within agro-ecological limits. These results are further used to assess the gaps with current production levels and required inputs to lift these levels.
Results
The global overview (Figure 1) reveals large potentials for growing grain crops in tropical regions where conditions allow the cultivation of two to three crops per year thanks to favourable temperature and water availability. Single cropping per year and lower potentials are obtained in temperate regions or where rainfall is limiting.
Figure 1. Calculated potential rainfed yields of maize or wheat (ton grain dry matter ha-1 y-1)accumulated for multiple cropping cycles per year in 5x5 min. grid cells containing crop land (see for methodology Conijn et al., 2011). Grey areas are either not suitable for crop growth or are not used as crop land.
A global map of yield gaps (rainfed – actual) has been constructed by using calculated values in combination with harvested areas and actual yields of maize and wheat (Figure 2). Most tropical regions show large yield gaps, whereas in more drier and temperate regions the actual yields can be higher resulting in negative yield gaps, because of irrigation (yields for rainfed conditions were used) and differences in crop varieties (e.g. situations where winter wheat is grown are compared with calculated spring wheat yields).
Figure 2. Calculated gap between potential rainfed and actual yields for maize (Central and South America, Africa, Southeast Asia) or wheat (North America, Europe, North and Central Asia, Australia and New Zealand) in 5x5 min. grid cells with respectively maize or wheat harvested areas (actual yields and harvested areas are from Monfreda et al. (2008; Global Biogeochem. Cycles, 22, GB1022, doi:10.1029/2007GB002947)).
The data illustrated in Figure 1 are used to calculate the total production for various global regions on crop land. The methodology has also been used to calculate the production on land covered by grass and forests (Figure 3). Especially, Africa and Central/South America have large potentials for crop production when converting grasslands and forests. Obviously, these areas are also claimed for other purposes, like grazing and biodiversity, and conversion into cropland would also have significant environmental effects, such as increased carbon emissions.
Figure 3. Total rainfed potential grain production (maize or wheat) calculated for three land use categories in various global regions (distribution of land use is from Erb et al. (2007; Journal of Land Use Science, 2: 191 — 224)).