ARKANSAS CORN AND GRAIN SORGHUM. Final Report. Optimizing Soil Fertility Requirements for Corn. Leo Espinoza, Soils Specialist, University of Arkansas

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1 D D Title: PI: Goal: ARKANSAS CORN AND GRAIN SORGHUM Final Report Optimizing Soil Fertility Requirements for Corn Leo Espinoza, Soils Specialist, University of Arkansas Increase Nitrogen Fertilizer Use Efficiency in Corn Objective]. To study tlte implications of delayed nitrogen applications in corn yields. Research plots were established at the Northeast Research and Extension Center (NEREC) near Keiser, and at the Rohwer Research Station (RRS) near Rohwer, during 213, 214, and 215. The soils are mapped as Sharkey silty clay at NEREC and RRS (213 only), and as Desha silt loam at RRS during 214 and 215. In 214, the NEREC trial was lost due to considerable lodging caused by strong winds and will not be reported. The preceding crop at both locations was soybean [Glycine max (L.) Merr.] in 213 and com in 214 and 215. Soil samples were collected during the spring of each year, from the shoulder of existing beds or before beds were fanned. One eomposite soil sample fron1 the -6 inch soil depth was collected from each location, each year. The soil was extracted for plant-available nutrients using the Mehlich-3 procedure (Table 1). Nitrate-N was determined with an ion-selective electrode, and ph was measured in a 1:2 soil: water (vol:vol) mixture. Soil fertility levels were optimum. During 214,.5 lb Zn/acre was applied after com emergence at each site. Treatments consisted of an application of 8-1 lb N/acre at emergence, followed by a sidedress application of 1, 12 or 14 lb N/acre, depending on soil texture, at one of four different growth stages including V4-V6, V6-V8, V8-V1, and V1-VT (Table 2). Plots received an additional application of 46 lb N/acre at VT. The total-n applied was 286 lb N/acre for clayey soils (NEREC and RRS 213) and 246lb N/acre for silt loam soils (RRS 214 and 215). The fertilizer-n source used for all N applications was urea amended with a recommended rate of an NBPT -based urease inhibitor to reduce ammonia volatilization loss. The only exception was during the 215 season, when ammonium sulfate was applied as part ofthe preplant N (1 lb/a). The fertilizer was applied by hand to each plot for each application time. The planting date at each site is listed in Table 2. Each trial included two ofthe most popular hybrids and varied from year-to-year including: Pioneer 1615HR and DeKalb hybrids were planted in 213, Pioneer 1319HR and DeKalb were planted in 214, and DeKalb 628 and Pioneer 289AM were planted in 215. Com was planted to achieve an intended population of 32, plants per acre. At maturity, the two middle rows of each plot were harvested with a plot combine equipped with a weigh-system and grain moisture meter. Yields were adjusted to 15.5% moisture content for statistical analysis. Statistical analysis was performed by site using the GLM procedure in SAS v9.2 (SAS Institute, Inc., Cary, N.C.). At RRS, treatments were arranged as a 2x4 factorial (2 hybrids and 4 application times). At NEREC, treatments were arranged as a 2x4 factorial as well, with the exception of213 when the two hybrids were planted as separate tests. Treatments were 57

2 replicated five times. Mean separations were performed using the Fisher's Protected Least Significant Difference method at a significance level of.1. RESULTS AND DISCUSSION The grain yields of both hybrids at NEREC during 213 may have been affected by the relatively late planting date (May 16). Results show significant yield loss when the sidedress-n application was delayed until after the V8-VI growth stage (Table 3 ). There is no good explanation for the abnormally low yield of 144 bu/acre observed for the DeKalb hybrid receiving the sidedress-n at the V8-VI stage. For the RRS in 213, the statistical analysis showed that hybrid and the hybrid by sidedress-n application time had no significant effect (P >.1 ) on grain yield (Table 3). A significant yield loss occurred when the N-sidedress application was delayed until after the V6- V8 growth stage. Overall, grain yields from both trials in 213 were probably affected by adverse weather conditions that did not allow planting until mid-may, a month later than normal (Table 2). Com planted at RRS in mid-may normally yields 15-2% lower than com planted in mid-april (Jason Kelley, personal communication). During the 214 season, weather conditions were very favorable to grow corn at the RRS, and the test was planted m Apnl on a sotl wtth good yield potential (Table 2). The statistical analysis of214 RRS grain yield data showed no differences between hybrids and both hybrids responded to sidedress-n application timing the same (non-significant interaction, Table 3). Corn yields were reduced by 8% when the sidedress-n application was delayed until after the V 6-V8 stage compared to the conventional application timing (V4-V6). During the 215 season, logistic and weather conditions did not allow for separate fertilizer-n applications at the V6-V8 and V8-V 1 growth stages at either location (Table 2). As observed in previous years, in 215, both hybrids followed the same yield trend as evidenced by the lack of significant interaction (Table 3 ). For the NEREC location, significant yield loss was recorded when the sidedress-n application was delayed beyond the VlO stage. At the RRS, no significant yield difference was observed among treatments. A possible explanation for the contrasting results is the amount of residual inorganic-n present in the soil before planting (Table 1 ). The soil residual nitrate concentration was 46 ppm for the RRS suggesting that com may not have required fertilizer-n to produce near maximal yield. The hybrid effect was significant at RRS during 215, with Pioneer 289AM yielding significantly more (233 bu/a) compared to DeKalb 628 (211 bu/a). For all site-years except RRS in 215, there was an obvious numerical trend for com yields to decline as the sidedress-n application was delayed past the V 1 growth stage. The purpose of these studies was to quantify the yield Joss potential when the sidedress-n application was delayed beyond the V4-V6 growth stage. Growing conditions during a particular season, native or residual soil-n availability, and the amount ofn applied before or by planting could affect the outcome of a study of this nature. Under the conditions of these studies, delaying the sidedress-n application beyond the V8 growth stage increases the risk of significant yield loss. The two com hybrids used each year appeared to respond similarly to the sidedress-n application timing. 58

3 Table 1. Selected soil chemical properties from the - to 6-inch soil depth at the Northeast Research and Extension Center (NEREC) and at the Rohwer Research Station (RRS). Composite sm 1 sam pies I were co II ecte d. m t h e spnng,. b e fl ore p1 I antmg.. Location Year ph N3-N pa Ka zna caa ppm ppm ppm ppm ppm NEREC RRS RRS RRS NEREC a Mehlich-3 extractable nutrients Table 2. Dates of planting and preplant-, sidedress-, and pretassel-n application for trials conducted at the Northeast Research and Extension Center (NEREC) and Rohwer Research Station (RRS) in 213, 214, and 215. Fertilizer-N Application Times a Location Year Planted Emergence V4-V6 V6-V8 V8-V1 V1-VT VT month -day NERECb 213 May 16 May29 June 7 June 17 June 24 July 2 July 16 RRSb 213 May 11 May24 June 5 June 14 June 25 July 5 July 1 RRSC 214 April 19 April29 May9 May2 June 3 June 12 June17 RRSC 215 April22 April3 May 21 June 3 June 3 June 19 June 19 NERECb 215 May 1 May8 June 4 June 1 June 1 July 2 July 2 a Fertilizer-N was apphed preplant at 8-1 lb N/acre, 1, 12 or 14 lb N/acre at one ofthe four sidedress application treatment times (V4-V6, V6-V8, V8-V1, and VlO-VT) and 461b N/acre at VT. h Fertilized with a total of 286 lb N/acre. c Fertilized with a total of 246 lb N/acre. 59

4 [] Table 3. Com grain yield means as affected by fertilizer-n sidedress application time in five trials conducted at the Northeast Research and Extension Center (NEREC) and Rohwer Research Station (RRS) in 213,214 and 215. Sidedress NEREC 213 RRS 213 RRS 214 NEREC 215 RRS 215 NTime P1615HR DeKa1 b Hybrid mean Hybrid mean Hybrid mean Hybrid mean (bu/acre)t V4-V6 162 a 169 a 177 a 296 a 176 a 229 V6-V8 165 a 16 b 173 a 283 ab V8-Vl 163 a 144 d 162 b 272 b 157 b 219 V1-VT 153 b 153 c 155 c 271 b 144 c 218 LSD Ns: C.V.,% NTime Hybrid Interaction t Means within a column followed by different lowercase letters indicate statistically different yields. t NS, not significant. Objective 2. To assess the use of pop-up fertilizers (liquid fertilizer with the seed) as a way to increase nitrogen use efficiency and seedling vigor. Plots were planted at the Cotton Branch Station, during with treatments including, 2 or 4 gpa of a liquid fertilizer applied with the seed. The fertilizer was applied with a vacuum planter equipped with a Keeton Seed firmer. There has been a consistent increase in seedling vigor for plots receiving the fertilizer with the seed. However, only in 213 we observed a significant yield response (Table 4) 6o

5 Table 5. Average yield response of com to pop up fertilizer Treatment bu/a t Check 187 b 181 a 19 a 2 gpa 196 ba 189 a 2 a 4 gpa 199 a 192 a 197 a t Means within a column followed by different lowercase letters indicate statistically different yields. There was a signiticant yield increase observed when using the pop fertilizer, especially at the rates needed to maximize yield potential. However, this trend was not statistically different due to significant variability among treatments. We noticed that treatments that had received infurrow fertilizer reached the VT stage 3-4 days earlier than the untreated plots. For these studies, we used a fertilizer with a salt index below 2, with K2S4 as the potassium source and a food grade phosphorus source. Objective 3. To study the interaction of seeding rate and nitrogen needs for selected hybrids. Plots were established at the NEREC near Keiser, the SEREC near Rohwer, and at the Lon Mann Cotton Reseaxch Station Com intended popylation was 25,, 35, and 45, plants per acre, with N rates being 2, 25, 3 lb/acre (for silt loams) and 25, 3, and 35 lb/acre (for clayey soils). Plots consisted of 4 rows wide by 25 ft long, and replicated 4-5 times. D Table 6. Average yield response of com to varying plant population and N nitrogen rate at SEREC (Rohwer). 213 (Clayey soil) (Clayey soil) Density P1319 DK64-69 P169 DK64-69 P bu/acre t , 45, 25, 119 c 254 c 242 b 187 b 146 b 265 b 247 b 222 a 163 a 278 a 272 a 232 a 196 c 225 b 244 a 118 b 135 a 137a N rate 2 (25) 134 b 26 a 242 b 29 a 225 a 13 a 25 (3) 145 a 267 a 26 a 29 a 221 a 132 a 3 (35) 148a 27 a 26a 213a 219a 135a t Means within a column followed by different lowercase letters indicate statistically different yields. 61

6 Table 7. Average yield response of com to varying plant population and N nitrogen rate at SEREC (Rohwer) Density P169 P169 DK , 35, 45, --- Yield bu/acre c 144 b 172 b 157 a 23 a 157 a 167 b 182 ba 185 a N rate b 17 b 147 a ba 188 a 154 ba a 177 ba 156 a t Means within a column followed by different lowercase letters indicate statistically different yields. Table 6 and 7 show average yields and associated statistics for studies conducted at both Keiser (NE) and Rohwer (8E) during The studies at Keiser were lost in 214 dtte to strong winds. Overall there was a significant yield response to increasing plant density over the standard 35, plants per acre. However, such yield increase was not consistent and appeared to be affected by hybrid, planting time, soil type, and weather conditions during a particular season. The statistical analysis showed that in those situations where a yield increase was observed, no additional nitrogen appeared to be required to maximize yields. 62