This was the question Douglas Gollin and colleagues at the University of Oxford sought to answer in a recent study published in the Proceedings of the National Academy of Sciences (PNAS). Bringing together surveys conducted in six African countries over 12 years, they gathered data on agricultural inputs, outputs and production practices from 55,000 households at an individual plot level. Strikingly, the study found that total factor productivity, taking into account fertilizer and pesticide usage, land-use and labour in relation to crop yield, did not increase between 2008 and 2019. While other studies have reported modest improvements, this study in fact found an overall decline in productivity of −3.5%, despite large-scale investment.

There are number of reasons why productivity of smallholder farms may have stagnated in recent years. It is difficult to know how productivity would have fared without investment, and it is possible that gains have been masked by yield penalties occurring as a result of climate change, pest pressure and declining soil fertility. It can also take many years before investments into agricultural research deliver long-term benefits, taking time for knowledge creation and technology adoption to spread. But if time lags and challenging environmental conditions alone cannot account for lack of progress in doubling productivity, it raises the question as to why these investments have borne so little fruit?

这是牛津大学道格拉斯·戈林 (Douglas Gollin) 及其同事在《美国国家科学院院刊》 ( PNAS ) 上发表的一项最新研究中试图回答的问题。他们汇集了 12 年来在六个非洲国家进行的调查，收集了 55,000 个家庭在单个地块层面的农业投入、产出和生产实践的数据。引人注目的是，该研究发现，考虑到与作物产量相关的化肥和农药使用、土地使用和劳动力，全要素生产率在 2008 年至 2019 年间并未增加。虽然其他研究报告了适度的改善，但这项研究实际上发现尽管进行了大规模投资，但生产率总体下降了-3.5%。

近年来，小农农场的生产力可能停滞不前，原因有很多。很难知道如果没有投资，生产力会如何发展，而且气候变化、虫害压力和土壤肥力下降导致的产量损失可能掩盖了收益。对农业研究的投资也可能需要很多年才能带来长期效益，知识创造和技术应用的传播也需要时间。但如果时间滞后和环境条件的挑战本身并不能解释生产率翻倍方面缺乏进展的原因，那么这就提出了一个问题：为什么这些投资收效如此之小？