IRRI agronomy challenge: when to harvest?
When to cease irrigating and then to harvest a rice crop is a tough question. We’re at 103 days after sowing, getting close to maturity.
We looked at it today with Martin Gummert, IRRI engineer and postharvest specialist , considered the average maturity of the panicles, the moisture in the soil, the type and depth of the soil and the weather outlook.
Most panicles have about 50% yellow grains, but this varies quite a bit throughout the field. Those smaller, later panicles nestled down in the canopy are almost all green, whereas some others are more or less matured. Martin brought along a grain moisture meter and we came up with an average estimate of about 28-30% grain moisture. Still quite some time needed to really reach harvestable maturity. The soil is still on the dry-end of mud. We know it is a heavy clay and we know it is deep (refer to the first few video clips of this Agronomy Challenge!), so there is quite a bit of available water in there. The weather looks dry, so we have to assume it will stay dry for the next two weeks.
Another consideration is lodging risk. We already saw this morning a few patches in which the crop has started to lodge. Perhaps a common feature in high-yielding crops (we hope), but we also have a suspicion that those were the places where we spread the fertilizer that was left over in the bucket, whenever we had reached the end of the field. A stark reminder that a little bit too much is not always good.
Martin Gummert (left) and Leigh Vial (right) check the moisture content of the crop.
Summing it up: if we were hand-harvesting, we could well consider another irrigation event, just to make sure. Yet, we will combine-harvest our field, so in such a deep, soft soil, we agreed that we had better keep the water away. It is no fun for man or machine harvesting whilst up to your arm-pits in mud. Hence, we will do...nothing. Time to check, adjust and grease the combine. Time for Achim to re-discover memories of combine-harvesting from deep in his past. Time to hope that it does not lodge much more.
By the way, Nancy’s team came out again a week ago to do another crop health assessment. The main crop injuries they found were stemborers (4.5% whiteheads), leaffolder (16%) and false smut (7.8%). Considering that we didn’t spray any insecticides or fungicides this is not surprising, and may not mean much in terms of the overall economics. We’ll come back to that when we analyze our final performance.
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