Darwinian Agriculture Talks at IRRI 1

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My talks at the International Rice Research Institute are have been posted on Youtube and have already "gone reptile" or whatever you call it when a few people watch them.

I've been enjoying my meetings with staff here. Some highlights so far:

Paul Hilario, curator of the IRRI museum, told me about the "community rat-barrier" strategy for reducing rat damage to rice. A small plot of rice is surrounded with a fence with a few holes. Rats are attracted to the plot and crawl in through the holes, each ending in a trap, so most of them are killed before they can reproduce. Sort of a black hole for rats. But it only works if the "trap plot" is more attractive to rats than other rice nearby. So coordination among farmers (planting nearby rice later than the trap plot) is key.

Next I met with Ruaraidh Sackville Hamilton, who's responsible for IRRI's 100,000-genotype rice collection. Here's a great story about that. He mentioned another example of cooperation among farmers being key to disease control. If every farmer in a region plants the same barley variety, that increases the risk of disease epidemics. So farmers in the UK coordinated choices to ensure high levels of diversity, at a regional scale. I don't know if this works better than if each farm had high levels of diversity, but it's probably better than if one farmer had high diversity and her neighbors didn't.

John Sheehy's seminar was another highlight of my first day at IRRI. He initiated a program to develop rice with the efficient C4 photosynthetic pathway, with funding from the Gates Foundation. That work is being continued by Paul Quick. They're using some very clever approaches, which I'll discuss in a later post, but success isn't certain and it will certainly take a while. So, Sheehy asked, what else can we do to increase the yield potential of rice?

Sheehy presented a bunch of simple equations: photosynthesis equals solar radiation times the fraction of that radiation intercepted by green leaves, times a radiation-use efficiency term, and so on. This overall approach is similar to what I used to teach in my Crop Ecology class at UC Davis, which I inherited from Robert Loomis. (Sheehy and I each taught the class as sabbatical replacements for Loomis, years ago, and we've both published on the physiology of legume root nodules.)

Sheehy pointed out that maximum yield occurs at the point when net growth is zero, that is, when biomass gets large enough that maintenance respiration balances photosynthesis. Maintenance respiration increases with temperature, so maximum yield will be less in warmer climates. This explains some yield differences that had previously been attributed to better cultivars or better management. I suspect that maximum production per day occurs much earlier than maximum yield, so it may make sense to harvest and plant another crop rather than waiting. Hoping to discuss this with Sheehy.

He also pointed out that leaves aren't important only for photosynthesis, but also as a place to store nitrogen which eventually gets used for grain nitrogen. You don't want the leaves so close together that they shade each other, so there are limits to how short rice plants should be, even though investing resources in stems rather than grain seems wasteful.

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