Narrowing the Conventional Versus Organic Farming System Yield Gap

Nearly everyone agrees that producing ample, nutritious and safe food to feed 9 billion people, with minimal harm to the environment, is one of mankind’s grand challenges. In the May 14, 2014 issue of National Geographic, Jonathan Foley sets out a thoughtful, five-step plan that highlighted these imperatives:

• “Freeze agriculture’s footprint” (e.g., stop clearing tropical rainforests),
• “Grow more on the farms we’ve got” (close the yield gap, more multi-cropping),
• “Use resources more efficiently” (help farmers “get smarter”),
• “Shift diets” (more fresh fruits and veggies, less grain-fed meat), and
• “Reduce waste” (25% food calories wasted; 50% of food by weight).

Three other critical changes are also going to be important: reducing poverty, empowering women, and investing in basic, food system infrastructure (roads, storage, bio-fertilizer plants, trained soil health and IPM experts, etc).

Transitioning more land to organic production systems will advance the ball in three of the above areas, but must it do so at the expense of # 2 – ability to grow more on existing farms?

Key insights on this question are evident in the results of a meta-analysis published December 10, 2014 in the Proceedings of the Royal Society of London (the U.K. equivalent of the Proceedings of the National Academy of Sciences).

A team from U.C. Berkeley led by Dr. Claire Kremen analyzed the yield impacts of organic vs. conventional systems in 115 studies that met strict inclusion criteria.  Dozens of crops were included in the more than 1,000 comparisons.  The paper – “Diversification practices reduce organic to conventional yield gap” – highlights opportunities to markedly close the yield gap through common diversification strategies like multi-cropping and crop rotations.

Earlier studies have estimated the organic versus conventional yield gap at around 25% (about the same magnitude as the “antioxidant gap” that favors organic, see our July, 2014 meta-analysis of the nutritional differences between organic and conventional food).  But in this new study on yields, across all comparisons, harvested organic yields were 19% lower than conventional yields, with the largest and most consistent gap in nitrogen-dependent cereals.  But when cereals are grown in rotations, the yield gap falls by one-half or more, to below 10%.  And among leguminous crops, the gap largely disappears, no doubt mostly because they affix much of their own nitrogen.

Another key finding warrants reflection among those working hard to push organic yields higher. In high-nitrogen and high-yield organic systems, yield variability increases. By eliminating N-based yield constraints, organic farmers sacrifice resiliency, just as conventional farmers do, and likely for most of the same reasons.

This interesting finding drives home a key point — organic and conventional farmers are bound by the same ecological, biological, and genetic “rules” of the farming road.

The paper’s discussion of the yield-enhancing benefits of rotations would have benefited from a few sentences and references to recent research on the “Continuous Corn Yield Gap,” what used to be called the “rotation effect.” Corn and soybean yields are 15% to 20% higher on farms rotating crops, as opposed to continuous corn or continuous soybeans.

Both conventional farmers and organic farmers can exploit the rotation effect and capture the benefits of diversity, or pay the consequences of not doing so. It’s just that simple.

As I read the paper, I thought of two other factors that future comparison studies need to find a way to take into account. First, the loss of near-mature fruit and vegetables on organic farms to insects and pathogens is greater than in conventional systems because organic farmers often lack quick-hit control options when there is a late-season influx of adult insects or pathogen spores.

My “best guess” is that ~1/3 of the organic vs. conventional fruit and vegetable yield gap is really caused by the late-season, “crop protection options” gap.  But there is good news – this gap is highly amendable to incremental improvement if appropriate R+D investments are made.

Second, the impacts of organic management on yields are highly dependent on a farmer’s experience and skill, and time since transition, regardless of baseline soil health, or lack thereof.  Why? The art and science of organic farming requires deeper and more intimate understanding of place, of cycles, the impact of recent weather on pests and soil fertility, etc.  Organic farmers must effectively manage more complex systems and biological interactions in real time, with fewer off-farm tools to drive mid-course corrections.

Take a look at this provocative paper.  For those interested in the details of advanced meta-analysis, and able/willing to wade deep into the statistical weeds, the 53 pages of supplemental material are worth a careful look.