Corn Harvest 2018

We harvested our corn on August 28 this year. Experiment 1 (EXP1) consisted of Plots 1-20, (4 treatments, 5 reps) while Experiment 2 (EXP2) consisted of Plots 21-40, (also 4 treatments, 5 reps). Results are shown in Table 1. A few thoughts here: (1) yields were disappointing (average of 96 bu vs. 134 bu in 2016) this can be attributed to a dry spell and compaction, that was probably the result of a poor cover prior to the corn. According to Farmer Carl, they saw a 20-30 bushel yield increase in the same field and soil series (Orangeburg loamy sand) just outside the plots where they subsoiled (first time in 5 years). (2) there was no significant difference between any of the treatments in either experiment (Table 1) - and this may well have been as a result of the dry spell.

 

Table 1: Corn Yield for 2018 by Fertilizer (N-P2O5-K2O) Treatment using the Fisher LSD Method at 95% Confidence.

Before we discuss individual effects of N and K2O, Table 2 shows the same results minus two outliers for Plots 20 and 40. Both of these plots are in very light land, still mapped as a Orangeburg, but we suspect this is actually a Lucy sand soil series. The result was a yield of 44 and 46 bu/ac for Plots 20 and 40 respectively - unfortunately both in the 60-0-0 treatment (plot randomization is not always perfect). Both results are considered outliers with a standard outlier (Grubbs) test at 95% confidence.

 

Table 2: Corn Yield for 2018 by Fertilizer (N-P2O5-K2O) Treatment using the Fisher LSD Method at 95% Confidence. Note that outliers for the 60-0-0 treatment in both experiments were removed.

Effects of N: If we consider the yield response to 30-0-0, 60-0-0 and 90-0-0, notice that in both Tables 1 and 2 there is no statistically significant fertilizer effect. In Table 1, the response to N (although not significant) follows the N application rate. If we remove the outliers, we get Table 2, and in both experiments, the 60-0-0 treatments beats out 30-0-0 and 90-0-0. My interpretation right now would be that this is the treatment that did best under drought stress, i.e., the demand for moisture when the dry spell hit was not as high as the demand in the (possibly bigger) plants fertilized with 90 units of nitrogen. So, in the case of dry weather, the optimum N rate was 60 units rather than 90 units.

Effects of K2O: A direct comparison of the N-P2O5-K2O treatments 90-0-0 and 90-0-90 (Tables 1 and 2 are identical) show that in both Experiment 1 and Experiment 2 the 90-0-90 (i.e., the recommended 90 units of K2O) under-performed compared to where the same amount of N was applied but no potassium. In reality the K2O applied was 150 lbs of potassium chloride - KCl or muriate of potash - my interpretation of this result is that the KCl actually increased the salt load and hence the drought stress on the plant. Whatever my interpretation, in all cases, the addition of KCl appears to suppress yield.

We are waiting until November to take soil samples.

Any questions are welcome!