I often get questions asking how varietal choice can impact nitrogen (N) management. To begin answering this question, we conducted a trial at two locations in California that examined nine varieties at six N rates ranging from 0 lbs. to 230 lbs. N per acre. The N was all applied as aqua in a basal application. For the varieties, we evaluated all of the commercial medium grain varieties (M-105, M-206, M-209, M-210 and M-211), two long grain (L-208 and Calaroma-201), and two short grain (Calakari-203 and Calmochi-203).
As you might expect, the highest yields were achieved with M-211, M-209, and L-208 (106-112 cwt/acre). The lowest-yielding varieties were Calakari-203, Calaroma-201, and Calmochi-203 (ranged from 90 cwt per acre to 100 cwt per acre). M-105, M-206, and M-210 were intermediate. Interestingly, despite the difference in yield potential, all varieties (except Calmochi, which required less) required a similar amount of N to achieve their highest yield. For these two studies, it was 190 lbs. N acre. Note that an optimal N rate of 190 lbs. N acre is higher than we typically see. Optimal N rates are usually between 150 lbs. and 180 lbs. N per acre.
We also looked at lodging potential. The most susceptible variety to lodging was M-105, Calmochi-203, and Calakari-230. Both M-206 and M-210 were also susceptible, but less so. For these varieties, you want to make sure that you do not over fertilize with nitrogen. M-209, M-211, and the two long grains (L-208 and Calaroma-201) had very little lodging — even at N rates that were more than optimal. In this study, we are also looking at how N rate impacts grain quality, but I do not have that data yet.
There are continued questions around reducing costs. I will touch briefly on how to potentially reduce fertilizer costs. First, think about not adding a top-dress N application. If you routinely apply top-dress nitrogen, consider applying all the N you would normally apply as a top-dress as aqua-N before planting. This saves cost, as aqua-N is a cheaper N source than ammonium sulfate (typical top-dress N source). Also, you avoid the airplane costs associated with topdressing. We have looked at this many times and have seen no impact on yield.
Secondly, if your field was fallow last year, you can reduce your N rate by 20 lbs.-40 lbs. N per acre. This is backed up by a lot of research showing more N is available from soils coming out of a fallow year. Importantly, for both strategies, it is important to keep a close eye on the crop around panicle initiation (40 days-45 days after planting) to see if it is displaying any signs of N deficiency. This can be done with Leaf Color Charts, a Green Seeker, or plant analysis — all of which have been discussed before. If the crop shows signs of deficiency, apply N.
Finally, test your soil. You may not need to apply phosphorus (P) and potassium (K) fertilizer. I recommend applying a balanced fertility program that balances the P and K removed from the field in harvested grain (and maybe straw) with what is applied as fertilizer. This is especially the case when soil tests are not used as it ensures an adequate supply of these nutrients. However, a decision can be based on a soil test. If your soil P levels are above 12 ppm (Olsen P/soil bicarbonate test), consider not applying P. Similarly, if your soil K levels are above 120 ppm, you may not need to apply K fertilizer. In areas on the east side of valley, especially the red soils, higher soil K levels may be necessary.
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