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Fluid Journal : Fall 2010
much higher broadcast rates and even in addition to broadcast fertilization. This was not the case for starter K. The K concentration of young corn plants was increased by one or more treatments at all sites (Table 1). Plant P concentration and uptake data are not shown or discussed. Broadcast fertilization was more effective at increasing K concentration than either starter PK or K at all sites, probably due to the higher amount of K applied. Starter PK increased K concentration more than starter K in sites 5 and 6. Starter PK, applied in addition to broadcast PK, increased K concentration further at four sites. Starter K, in addition to broadcast fertilization, increased K concentration further in three sites. Early corn K uptake data integrated results for growth and concentration (Table 1). Starter PK increased K uptake over the control in five of six sites, but starter K alone increased uptake at site 2 and decreased uptake at site 5. Starter PK applied in addition to broadcast PK increased K uptake further at sites 2, 5, and 6, but starter K decreased uptake at site 4 and increased it at site 5. Therefore, these results show that P, or PK together, play a major role in early growth and K uptake. Corn grain yield was increased by one or more treatments at five sites (Table 1). Site 3, the only non-responsive one, had the highest soil test values. According to current Iowa State University soil test interpretation categories, the probability of corn response is 80 percent for very low, 65 percent for low, less than 25 percent for optimum and less than 5 percent for high. At site 1 all treatments increased yield over the control and the increases were statistically similar. At site 2 all treatments increased yield but the increase was less for starter K applied alone (soil P was very low). At site 4, broadcast fertilization increased yield while the starter fertilizers did not. We do not understand why starter fertilizer did not increase yield at this site (there was a small increasing trend) since soil test PandKwereverylow.Atsites5and6, broadcast fertilization increased yield more than the two starter fertilizers. At site 5, both soil P and K were low while at site 6 P was low and K was optimum. Applying starter in addition to broadcast PK never increased yield further. These results showed that early growth and nutrient uptake responses to starter do not necessarily result in grain yield increases. Strip trials By field. Potassium fertilization effects on corn early growth were significant (P≤0.10) in five sites, but effects were inconsistent (Table 2). In field 2, starter K alone increased early growth slightly but all other treatments decreased it. In field 3 (a no-till site), broadcast K increased growth slightly, starter K did not affect it, and application of starter in addition to broadcast decreased growth compared with broadcast applied alone. In field 4 (the other no-till site), broadcast K did not affect growth but starter K decreased it when applied alone or in addition to broadcast K. In field 8, broadcast K did not affect growth but starter K applied alone decreased it. The inconsistent and small early growth responses to broadcast or starter K fertilization across fields could not be explained by the soil test K level or any other measurement taken. Salt effects on roots and water uptake might explain a growth reduction from applied K, but we doubt this was the case in our study. Field observations indicated that no treatment reduced corn plant population significantly at any field. Broadcast rate of K2O at 120 lbs/A as potassium chloride did not decrease early growth at the no-till fields but decreased it in some fields managed with tillage. This K rate incorporated into the soil with tillage should not affect growth. The low salt 0-0-30 fertilizer (potassium carbonate) applied to the seed furrow at K2O rates of 15 to 22 lbs/A did not result in obvious salt effect symptoms nor decreased stands. Therefore, we believe that the results reflect no K effect on early corn growth, and that the inconsistent (and often small) increases or decreases resulted from variability in other growth factors. The results of the small-plot studies also showed infrequent and inconsistent effects of starter K on early corn growth. In contrast to results for early corn growth, K fertilization often increased early plant K concentration (Table 2). In four fields (3, 5, 6, and 7) all treatments increased plant K concentration with the increases being largest for broadcast K alone, then for starter K alone, although the difference was not statistically significant in field 6. Application of both broadcast and starter K resulted in the highest early K concentration except in field 7. At field 8, however, Table 1. Phosphorus and potassium fertilization effects on early corn growth and K concentration (V5 to V7 stage) and grain yield for six small-plot trials. Broadcast 3-18-18 Starter 0-0-30 Starter Site Control P-K Alone Alone +Broad P-K Alone + Broad P-K Plant Dry Weight (g/plant) 1 10.7 11.5 10.2 11.7 10.7 11.3 2 2.0a† 2.4c 2.5c 2.6c 2.2b 2.6c 3 1.2b 1.7d 1.8d 1.9d 1.1a 1.6c 4 2.5b 3.9d 3.2c 3.6d 2.0a 3.2c 5 2.7b 3.1b 3.5c 4.4d 2.4a 3.6c 6 3.3a 4.6c 4.6c 6.4d 3.5b 4.5c Plant K Concentration (%) 1 2.53a 3.95c 2.17a 3.53b 2.55a 4.54d 2 2.40b 3.09c 2.38a 3.51d 2.38a 3.38d 3 4.17a 4.42b 4.07a 4.67d 4.08a 4.62c 4 2.25a 3.87b 2.61a 4.10b 1.91a 3.84b 5 2.34b 3.86d 3.22c 4.52e 2.22a 3.69d 6 1.62a 3.26e 2.47c 3.60f 2.10b 3.02d Plant K Uptake (mg/plant) 1 281a 460b 237a 414b 267a 516b 2 48a 76c 59b 93d 53b 88c 3 50a 73b 71b 86b 46a 75b 4 57a 154d 87b 150d 39a 125c 5 69b 121c 117c 199e 57a 135d 6 55a 152b 133b 244c 74a 136b Grain Yield (bu/acre) 1 161a 193b 182b 184b 185b 189b 2 159a 176c 176c 185c 171b 178c 3 179 177 183 183 173 183 4 171a 210b 172a 209b 175a 209b 5 169a 204d 184b 205d 184b 195c 6 129a 170c 147b 163c 154b 172c Numbers in a row followed by no letter or a similar letter do not differ (P < 0.10) 13 The Fluid Journal Fall 2010
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