IRRI agronomy challenge: wrapping-up and looking back
Today we sat down in the coffee shop to evaluate what we accomplished. There is nothing better than doing a bit of self-critical learning. Remember, we set out to grow a rice crop with a yield goal of 7 t/ha, and we had hoped that by applying best management practices we’d achieve that with good efficiency of critical inputs, and thus also turn in a decent profit. So, we looked at yield gaps and we produced a simple crop budget sheet.
Let’s look at yield first. We came out at 5.24 t/ha rice (paddy at 14% moisture) in the bin, so why didn’t we achieve 7 t/ha? There were three major reasons (types of yield gaps):
Achim Dobermann and Leigh Vial look back and assess how they fared in their first Agronomy Challenge.
• Bad weather. To assess that, we ran a crop growth simulation of the theoretical yield potential of rice for the actual weather encountered in our dry season, and for each of the 20 years before (1992-2012). We used the ORYZA2000 model, which assumes no growth limitations or yield losses by water, nutrients or pests. It simulates the ideal crop, a theoretical maximum one can only get with perfect management. The simulated long-term average yield potential was 10.6 t/ha with the model settings chosen, but it was only 8.7 t/ha in our cropping season. In other words, because we had many cloudy days with less sunshine and also quite frequent rains, we seem to have “lost” nearly 2 t/ha in terms of yield potential. A model makes of course many assumptions and these values may not be the absolute truth, but the fact remains that, in terms of weather, we picked one of the worst years in the past 20 or 30 dry seasons at IRRI. Not a good starting point for wanting to prove something. It probably resulted in lower grain filling percentage, as we also observed in many panicles. There’s not much we could do about that yield gap.
• Grain losses due to lodging/combine harvest. We lost at least 0.6 t/ha grain during harvest, when the crop had heavily lodged and we were not able to adjust the combine enough to avoid major shattering losses. The lodging occurred during final grain filling and was probably a coincidence of wet conditions and the variety chosen. The yield we had standing in the field was actually around 5.9 t/ha.
• Yield losses due to variable crop establishment and pests. We don’t think that we were short of nutrients or water at any point during the crop cycle, but we struggled with getting an even crop stand (had to re-seed and even re-plant in some areas). During vegetative growth we had quite severe rat damage (>8% incidence) and leaf damage due to whorl maggots (25% incidence). At later stage, in April, we had significant incidence of stemborer (>5% whiteheads), leaffolder (16%), false smut (8%) and weeds (>5%) to name a few. All of these crop management-related losses must have contributed to the yield gap between the 8.7 t/ha simulated yield potential and the 5.9 t/ha standing yield at harvest. Clearly, that is the major opportunity for further improvement.
Achim Dobermann (left) and Leigh Vial discuss
how they fared in their first Agronomy Challenge
Leigh came up with a basic crop budget sheet, including the income generated from selling the paddy US$ 1747/ha) vs. all our expenses (US$ 1412/ha). Purists may argue that we should have applied our real salaries to calculating the labor costs, but let’s just assume that we wanted to be like normal rice farmers and should use what they would pay for labor. Overall, we’ve been able to generate a profit of $335/ha, which is not unlike what many rice farmers would make in similar production situations.
On the positive side, we were quite low in terms of labor input and agrochemicals (no insecticides or fungicides). However, our largest product costs were for irrigation (electricity for pumping water, 37% of total cost) and fertilizer (25%), even though we did not over-apply any of those. If our water source had been from a canal in a government-run irrigation scheme, our net profit would have been at least twice as high.
All in all, it was a great learning experience. Get out there and try it yourself.
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