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Fluid Journal : Summer 2016
9 The Fluid Journal Summer 2016 starter fertilizer among High Plains corn producers. These efforts have illustrated the ease of application and low set-up costs compared with traditional 2 x 2 starter fertilizer placement. Another benefit of the 2 x 0 practice was that wet soils did not affect starter fertilizer placement that typically hampered traditional fertilizer coulters during planting. Precision guidance systems have made possible the latest fertilizer trend among growers. This program involves banding pre-plant fertilizer 8 to 10 inches deep during strip-till followed by planting over the band and using in-furrow popup starter fertilizer to achieve the highest yields. 4Rs. Nitrogen rates of 1.2 to 1.3 lbs per bushel of grain used by many soil test labs remains a standard when 100% of the N is applied prior to planting the crop. However, IPNI (2013) has emphasized the interconnectedness of the 4Rs of nutrient stewardship and how rate, time, source, and placement of fertilizer are interdependent. Thus, Table 2. N rate adjustments based on liming and method of application. N application timing and method N rate to produce a bushel of corn 100% pre-plant broadcast 1.3 lbs. 100% pre-plant band 1.2 lbs. 100% fertigation 1.1 lbs. 50% pre-plant and 50% side-dress 1.0 lbs. Pre-plant/starter/side-dress 0.9 lbs. Pre-plant/starter/side-dress/fertigation/post-tassel 0.8 lbs. Table 3. 2010 plot averages by timing N applications after tassel. No Post Tassel N Applied (19 Locations) Some N Applied at Brown Silk (21 locations) 217 bu/acre 248 bu/acre Low plot: 170 bu/acre Low plot: 183 bu/acre High plot: 269 bu/acre High plot: 302 bu/acre 3 plots over 240 bu/acre 14 plots over 240 bu/acre Table 4. Management practices for 2013 top 10 highest average plots. Location (County) Avg. Yield Plant Date GPM/a Tillage Starter Miticide (pre-tassel) Post-Tassel N Sherman 285.2 5-17-13 5.5 Strip Y Y Y Hansford 284.5 5-04-13 6.0 Strip Y Y Y Hansford 282.2 5-10-13 5.3 Strip Y Y Y Moore 281.4 4-30 -13 6.0 Strip Y N N Texas 280.9 5-17-13 5.6 Strip Y Y Y Ochiltree 275.0 5-17-13 6.0 Strip Y Y Y Sherman 267.2 5-13-13 5.4 Strip N Y Y Moore 265.4 4-29-13 5.0 Strip Y Y Y Texas 263.4 5-13-13 6.0 No-Till Y Y Y Hansford 262.7 5-22 -13 4.5 Strip Y Y Y N rate can be adjusted based on timing and placement without affecting grain yield. Our test plot data confirm this (Tables 2 and 4). Growers who apply a portion of their N pre-plant followed by starter, side-dress or via pivot at V4 to V6 stage, along with R2 to R4 (Ritchie et al., 1997) stage N application via center pivot, were able to produce a bushel of grain with 0.8 lbs. of N (Reinart, 2013). This practice can increase producer profitability because it allows adjustment of N rates based on in-season price fluctuations of N fertilizer, corn, or growing conditions. For example, high corn yields may not be possible for producers with limited available irrigation water in the absence of favorable growing conditions and precipitation. These growers can be conservative with fertilizer inputs and make in-season adjustments of N rates when growing conditions favor increased potential for grain yield. This practice also allows producers to reduce or eliminate N application following a catastrophic weather event such as hail. Furthermore, single high rate application of N increases the probability of stalk rot when environmental conditions favor these diseases. Multiple applications of N fertilizers through the season help reduce potential for stalk rot organisms to infect corn stalks (White, 1999). 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 at V4 to V6 and again at V 14 to VT (Richie et al. 1997) 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 area of the filed at R1 to R2 stage (Richie et al. 1997). 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 to R1 growth stages. Post tassel (post-flowering) application of N can increase yields by increasing kernel depth and test weight. Our test plot results have demonstrated a yield increase when N is applied from tassel to R4 growth stages (Tables 3 and 4). 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, as documented by Davis et al. (2012). This practice also allows the additional N when yield estimates exceed the producer’s original yield goal. A lower stalk nitrate test developed by Blackmer and Mallarino (1996) can be made on stalks collected at black layer to three weeks after black layer to determine the success of in-