One of the most famous experiments comparing chemical fertilizers and manure is the long-term study at the Rothamsted Experiment Station in England. Ever since the 1840s, wheat plots at Rothamsted have yielded roughly the same amount whether they were fertilized with farmyard manure or chemical fertilizers. From the late nineteenth century on, these plots have been used as proof that chemical fertilizers can supply everything plants need to grow and that the organic matter in manure is unnecessary.
The Imperial Agriculturist at the Imperial Agricultural Research Institute must have been familiar with the Rothamsted results. At any rate, he began a similar long-term fertilizer experiment at Pusa, India in 1907, comparing farmyard manure, chemical fertilizers, oilseed cakes, and green manures. Meanwhile, Sir Albert Howard—the Imperial Economic Botanist—was busy breeding wheat and improving vegetable production. He never cited the fertilizer experiments at Pusa. But he must have known about the results, which were strikingly different from those at Rothamsted.
By 1928, the fertilizer experiment at Pusa had been running for twenty years. At the time, statistical analysis was not standard and the plots were not replicated, with only one for each treatment. But since the experiment lasted so long, I decided to try running some statistical analysis on the results, treating the years as replicates. There was a lot of variation between years, but even so the results were extremely significant
As at Rothamsted, both farmyard manure and chemical fertilizers increased yields over an unfertilized control. But unlike Rothamsted, the yields from manure and chemicals were significantly different. Chemical fertilizers increased yields by 43 percent over the control, but farmyard manure increased yields by 97 percent over the control. The reason, as John Voelcker had observed way back in his 1893 Report on the Improvement of Indian Agriculture, was that organic matter—not N, P, or K—was the biggest limiting factor in Indian soils.
Whether it was because of this experiment or not, Sir Albert Howard eventually shifted his research emphasis from breeding to fertilizer. In his 1927 book The Development of Indian Agriculture, Howard reported the results of an experiment in which he had fertilized his improved wheat varieties with compost or chemical fertilizers. Compost-fertilized wheat had double the yields of chemically fertilized wheat.
As impressive as these results were, I wanted to see how they compared to the later introduction of Green Revolution wheats. Howard reported his yields in the archaic measurement of maunds per acre, which I converted to bushels per acre. It turns out that Howard’s compost-fertilized wheats were yielding 41.5 bushels per acre, compared to 20.8 bushels per acre for the average Indian cultivator in the region. For comparison, the average wheat yield in the US during that same time period was 13.7 bushels per acre. The US didn’t catch up with the 1920s Indian peasant until 1956 and didn’t match the yield of Howard’s compost plots until 1998. And India, despite the Green Revolution, didn’t get up to an average of 44 bushels per acre until 2011.
So next time someone says that organic farming can’t feed the world, just point to the Pusa studies and Howard’s research. Widespread implementation of the Indore Method could definitely have achieved the same yields—or even higher—as modern chemical farming.
Excellent work, AA! Fascinating history, thank you. I wonder how much of his compost Howard had applied per acre.