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Fluid Journal : Winter 2015
9 The Fluid Journal Winter 2015 reduce potential for stalk rot organisms to infect corn stalks. Tables 3 and 4 also witness to the importance of N timing on yield. Figure 1 shows a dramatic difference of post-tassel UAN in corn ear size compared to no late N. Post- tassel (post-flowering) applications of N can increase yields by increasing kernel depth and test weight. The newest corn hybrids use more N post-tassel than older hybrids of several years ago. Modern corn hybrids can respond well up to 33 percent of N goal going on between brown silk and dough stage. Finally, Figure 2 presents a 5-step ladder on the importance of proper corn N management. Monitoring Monitoring soil and plant N during the season has been a successful practice for farmers, particularly where manure or compost is the major source of N. This program entails sampling soil to a 30- inch depth from V4 to V6 and again from V14 to VT growth stages to determine nitrate and ammonia forms of N. Plant tissue samples are also collected following protocols established by Servi- Tech Laboratories. The protocol for estimating corn yield entails collecting ears in representative areas of the field at R1 to R2 stage. The number of kernels per ear is determined by multiplying the number of kernels per row by the number of rows. The test weight is considered to determine the factor used for estimating yield for each hybrid. Other factors considered when estimating yield include insect and disease pressure, soil moisture, weed control, and the 10-day weather forecast. Additional N can be applied in cases where soil N is inadequate at VT or R1 growth stages. Our test plot results have demonstrated a yield increase when N is applied from tassel to R4 growth stages. Monitoring N, along with R1 growth stage yield estimates, ensures the producer’s crop has adequate N at critical growth stages. The benefit to producers is a potential reduction in N expenditures if tests show levels are sufficient, and the possibility of applying additional N if manure conversion provides less than expected available N. This practice also allows for additional N when yield estimates exceed the producer’s original yield goal. A lower stalk nitrate test, developed by Blackmer and Mallarino, can be made on stalks Figure 1: Center pivot applied UAN post-tassel. Photo by Alyssa Abbott Pioneer Account Manager; NE Illinois Center Pivot applied UAN post tassel Corn Nitrogen Management Ladder 1 Banded N Application Preplant “Spoon Feed” Pivot application 100% Preplant N Band + Sidedress band (2X) Pre-Plant NPK band + Starter + sidedress/V6 fertigation (3X) Pre-Plant NPK Band + Starter + Side-Dress/V6 Fertigation + Brown Silk Fertigation (4X) Step 1 EfficiencyRating Lbs N/Bu 1.2 1.1 1.0 0.9 0.8 1.3 1 Broadcast Application Pre-Plant Floor Step 2 Step 3 Step 4 Step 5 Figure 2: Corn nitrogen management ladder. collected at black layer to three weeks after black layer to determine the success of in-season N applications. In 2013, an N monitoring project managed by DuPont Pioneer personnel was implemented on a 6,000-acre irrigated corn farm in the Texas Panhandle. Compost and manure are used extensively as a primary N source on these acres. The yield goal across these acres was 250 bu/A. Nitrogen recommendations were based on field and environmental conditions and lab results from soil and plant samples collected in mid-June (V5) and in mid- July (VT). Adjustments in N applications were made when needed, based on the condition of the crop. For example, fields damaged by hail received reduced rates of N and, conversely, fields with yield potential above 250 bu/A received additional N. The yield average across the 6,000 acres was 253 bu/A based on dry weight determined by a local