The potential for returning land to nature with high-yield farming
The continuous expansion of global cropland exerts substantial pressure on natural ecosystems. One option to halt this process is to spare land by achieving high crop yields. In a recent study we estimated how much land could be returned to nature if high-yield farming was realised globally.
The conversion of natural land to cropland entails wide-ranging adverse environmental impacts such as greenhouse gas emissions, soil degradation, and loss of wildlife habitat. Today, about 10% of the ice-free land surface are agricultural fields and another 15% rangeland, rendering agriculture a major impact on the Earth’s surface. In many regions, cropland productivity is fairly low, which can be caused by crops not grown under optimal climate conditions, lack of plant nutrients and water, planting of low-performing varieties, or exogenous stresses such as pests and diseases. This results in large land requirements to produce a given amount of crops. Conversely, farmers employing the most up-to-date production technologies achieve crop yields close to the crops’ genetic potentials.
To study how achieving such high yields would affect global crop production volumes, researchers have assessed how much crops or caloric value could be produced on present cropland if attainable yields were achieved and found that global crop production could be more than doubled.
This is valuable information considering that crop demands will likely increase in the future. Yet, at present, there is a given demand defined by requirements and preferences for food and non-food products, as well as efficiencies in the consumption chain. Assuming that present production volumes reflect the present demand, we figured that it would be interesting to estimate how much cropland mankind would require to meet this target with high-yield farming. To do so, we fed attainable crop yields simulated with an agronomic model together with land use information into an optimisation algorithm that allows the acreage of crops to change locally, in order to be grown where they are most productive, while aiming to minimise the global cropland extent.
Figure 1: Schematic of the high-yield farming for cropland sparing approach. First, attainable crop yields (shown here for sorghum and wheat) are estimated (left) and subsequently crops are redistributed to where they grow best on present cropland (right), resulting in the release of cropland in less productive regions.
This showed that under such a land-sparing optimised global cropping system, about half the present cropland could be released and potentially used for restoration or environmentally friendly landscape elements. However, when we also modelled impacts on habitats of threatened wildlife species, our results showed that only targeted land sparing for biodiversity would have a positive effect on these species’ habitats. Surprisingly, the global plant nutrient input requirements hardly changed compared to the present-day. Although cropland expansion and its extent as such allow for “mining” indigenous nutrients from soils or from atmospheric deposition on them, the present excessive application of fertiliser in some regions is apparently so large that the loss of land for nutrient acquisition can in principle be compensated.
The study is fairly hypothetical in assuming global free trade of crops, as well as a ready dissemination of technologies for high-yielding crop production and distribution, and neglects the local requirement of income-generation from farming. On the other hand, it provides a benchmark for biophysical global cropland requirements free from assumptions regarding such aspects. These will need to be addressed in future research, which may also include demand scenarios, the suitability of agro-ecologic farming systems to achieve land sparing targets, or the role of multi-cropping to develop a full picture of pathways and constraints to sustainable farming systems with a minimal land footprint.