Industrial agriculture could be hitting fundamental limits in its capacity to produce sufficient crops to feed an expanding global population according to new research published in Nature Communications.

The study by scientists at the University of Nebraska-Lincoln argues that there have been abrupt declines or plateaus in the rate of production of major crops which undermine optimistic projections of constantly increasing crop yields. As much as "31% of total global rice, wheat and maize production" has experienced "yield plateaus or abrupt decreases in yield gain, including rice in eastern Asia and wheat in northwest Europe."

The declines and plateaus in production have become prevalent despite increasing investment in agriculture, which could mean that maximum potential yields under the industrial model of agribusiness have already occurred. Crop yields in "major cereal-producing regions have not increased for long periods of time following an earlier period of steady linear increase."

The paper makes for ominous reading. Production levels have already flattened out with "no case of a return to the previous rising yield trend" for key regions amounting to "33% of global rice and 27% of global wheat production." The US researchers concluded that these yield plateaus could be explained by the inference that "average farm yields approach a biophysical yield ceiling for the crop in question, which is determined by its yield potential in the regions where the crop is produced." They wrote:

"... we found widespread deceleration in the relative rate of increase of average yields of the major cereal crops during the 1990–2010 period in countries with greatest production of these crops, and strong evidence of yield plateaus or an abrupt drop in rate of yield gain in 44% of the cases, which, together, account for 31% of total global rice, wheat and maize production."

Past trends over the last five decades of perpetually increasing crop yields were "driven by rapid adoption of green revolution technologies that were largely one-time innovations" which cannot be repeated. These include major industrial innovations such as "the development of semi-dwarf wheat and rice varieties, first widespread use of commercial fertilizers and pesticides, and large investments to expand irrigation infrastructure."

Although agricultural investment in China increased threefold from 1981 to 2000, rates of increase for wheat yields have remained constant, decreased by 64% for maize and are negligible in rice. Similarly, the rate of maize yield has remained largely flat despite a 58% investment increased over the same period. The study warns:

"A concern is that despite the increase in investment in agricultural R&D and education during this period, the relative rate of yield gain for the major food crops has decreased over time together with evidence of upper yield plateaus in some of the most productive domains."

The study criticises most other yield projection models which predict compound or exponential production increases over coming years and decades, even though these "do not occur in the real world." It notes that "such growth rates are not feasible over the long term because average farm yields eventually approach a yield potential ceiling determined by biophysical limits on crop growth rates and yield."

Factors contributing to the declines or plateaus in food production rates include land and soil degradation, climate change and cyclical weather patterns, use of fertilisers and pesticides, and inadequate or inappropriate investment.

The new research raises critical questions about the capacity of traditional industrial agricultural methods to sustain global food production for a growing world population. Food production will need to increase by about 60% by 2050 to meet demand.

A report out this month from the Dutch bank Rabobank recommends cutting food waste by 10%, as over 1 billion tonnes - half of which is related to agriculture - ends up being wasted. More efficient use of water is necessary, the report says, such as micro-irrigation, to address a potential water supply deficit of 40% by 2030. Currently, agriculture accounts for 70% of global water demand. The report also calls for a reduction in dependence on fertilisers using 'input optimisation' methods designed to reduce the amount of energy and water required. As 53% of fertiliser nutrients remain in the ground post-harvest, fertilisers contribute to soil degradation over time due to groundwater contamination, leaching, erosion and global warming.

The Rabobank obsession with focusing on improvement of existing industrial methods - without quite grasping the scale of the problems facing industrial agriculture - is, however, a serious deficiency. Two years ago, a landmark report by the UN Special Rapporteur on the Right to Food demonstrated that agroecology based on sustainable, small-scale, organic methods could potentially double food production in entire regions facing persistent hunger, over five to 10 years.

Dr Nafeez Ahmed is executive director of the Institute for Policy Research & Development and author of A User's Guide to the Crisis of Civilisation: And How to Save It among other books. Follow him on Twitter @nafeezahmed