By Jarrod Hardke, Rice Extension Agronomist
What a year it has been. By and large, it sounds like we’ll get very close to last year’s state average yield of 166.4 bu/acre, which was third highest behind only 2013 and 2014 which tied at 168. A couple of months ago I thought we would finish around 165 bu/acre, which would be a massive crop since we planted over 1.4 million acres this year. As it stands, USDA-NASS continues to hold us at 7,500 lb/acre (166.7 bu/acre) which would be the third highest yield on record just ahead of 2017.
However, there have been some interesting developments. Hybrid yields have been very good – some have referred to it as “a hybrid year”. Variety performance has been more variable and there are a number of likely reasons why. Let’s dig in:
- Nitrogen (N) efficiency
Hybrids take up soil N more efficiently than varieties. If I plant Diamond and XP753 side-by-side and fertilize with 120 lb N/acre, they’re both going to take up about 70% of that fertilizer-N. So, they take up fertilizer-N with similar efficiency, but what if something happens that increases N loss or minimizes the fertilizer-N available to plants? Then the plants must depend on their ability to obtain N from the soil to bridge the gap between what they need and what they received from us in order to maximize yield. Hybrids are better at this recovery of native soil N. So, in a hot dry year where it takes forever to flood – we are doing two things: 1) delaying N incorporation which delays plants getting the N, and 2) increasing N loss. In this scenario, hybrids are going to perform better.
- Yield decline by delaying preflood N
The critical period to establish the permanent flood and incorporate preflood N has been previously established. In the last few years, we’ve revisited this research with newer cultivars (Fig. 1). The big surprise was that there were no big surprises. The trends remained very much the same as in older research with older cultivars. The longer you delayed past the cutoff the lower your yield potential. However, there are some additional wrinkles we’ll be trying to tease out going forward.
Fig. 1. Percent of Optimum Grain Yield by Preflood N Timing (N Incorporation by Flood).
- Crop Maturity
As a part of the evolution of our rice production system, we have selected for earlier maturing cultivars. In doing so, the length of the reproductive period (green ring to heading) hasn’t really changed at all. Instead, we have shortened maturity almost exclusively by reducing the vegetative period (emergence to green ring). This makes timeliness of early-season management that much more critical because we reach optimum and maximum tillering that much faster now. Number of tillers per area is our first yield component – fail to maximize it and we’re already behind.
This is a little redundant, but record heat is part of what got us into this mess with some of the previous points. First, we had near record low DD50 unit accumulation for the month of April (Fig. 2). Then, we accumulated more DD50 units in the month of May than any year I looked at back to 1983 (Fig. 3). The next closest year was not even close. So, if we’re not running DD50 reports to keep us on schedule, or unable to stick with the schedule because conditions are so extreme, we’re going to be penalized for it. If you run DD50 reports for nothing else, it should be done on every field for N timing.
Fig. 2. DD50 Unit Accumulation for April 2018 at the Rice Research & Extension Center, Stuttgart, AR.
Fig. 3. DD50 Unit Accumulation for May 2018 at the Rice Research & Extension Center, Stuttgart, AR.
- Planting date
Planting date generally works out that the earlier we’re able to plant, the better our yields. That’s the way the data averages out, but it’s not the way it works in individual years every time. This year it was largely true for the southern half of the state. However, in the northern half, it actually seemed to be a little better to plant from mid-April on to achieve top yields. I still don’t have the perfect explanation for this, but early-season stress likely had a lot to do with it. The earliest rice was the most difficult to get fertilized and flooded. Data from planting date studies is shown in Figures 4 and 5 (the white band on each figure is the current recommended optimum planting window for that area of the state).
Fig. 4. Average grain yield for twenty cultivars across six planting dates at the Rice Research & Extension Center, Stuttgart, AR.
Fig. 5. Average grain yield for twenty cultivars across six planting dates at Pine Tree Research Station, Colt, AR.
Trial results referenced above were supported by Arkansas rice growers through the Arkansas Rice Check-Off and administered by the Arkansas Rice Research and Promotion Board.