How soil, water, and crop change along with farm sizes: insights from a new high-resolution farm-size specific and crop-specific map covering 56 countries

Over 608 million farms exist around the world, occupying 36.9% of global land and 72% of annual freshwater withdrawals. These farms are highly diverse and heterogeneous. More than 80% of them are smaller than 2 hectares and they only utilize around 20% of farmlands but support millions of livelihoods in the rural area. Many datasets are available describing the global crops, soil conditions, and water availability. A few of them are farm-size specific. There is a lack of a global overview on how the soil-water-agriculture system is different across farm sizes.
This study aims to explore how soil, water, and crop change along with farm sizes. Specifically, we used the current best available databases on cropland extent, farm size structure, crop-specific harvested area, and field size distribution to develop a gridded, farm-size specific, and crop-specific harvested area map for 56 countries, representing half global cropland, using a downscaling algorithm. The resulting maps were validated by empirical data and compared to previous similar studies. We then overlapped the farm-size specific, and crop-specific map with global soil and water scarcity maps to explore differences between small and large farms on planted crops, soil nutrient availability, and level of water scarcity.
Our results show, in comparison to larger farms, smaller farms plant more pulses, roots and tubers, vegetables, and fewer oilcrops, sugar crops, and fodder crops. The majority of small farms do not have severe limitations on soil nutrient availability, but they do face severe water scarcity. Large farms, on the other hand, do not confront severe water scarcity but do face severe limitations on soil nutrient availability. Small farms may also be less capable of adapting to water scarcity through irrigation. However, there is still spatial variation in our results. Our results can help to further differentiate the sustainable soil, water, and agriculture management for small and large farms.