Corn Kernel Weight and Grain Yield Stability during Post-Maturity Drydown

Some research reports suggest that corn (Zea mays L.) grain dry matter decreases 1% for every 1% loss in grain moisture after physiological maturity (R6) as corn dries in the field. This dry matter loss reportedly is hybrid specific. We conducted a 3-yr study at Clay Center, NE, to determine whether corn loses dry matter after R6 as it air dries. In 1995, hand-harvested ears were bagged and stored in two environments and hand-shelled on nine dates to determine kernel moisture and dry weight In 1996, five hybrids were planted and harvested at eight dates. Six hybrids were used in 1997. In both 1996 and 1997 three storage and sampling methods were used to determine kernel moisture and weight over eight dates: (i) laboratory storage; (ii) field drydown/hand harvest; and (iii) field dry-down/machine harvest. Neither processing date nor storage environment affected kernel weight as grain moisture decreased from 30 to 9%. In 1996 and 1997, corn grain yields did not differ among the eight harvest dates nor was there any interaction between hybrid and harvest date. Although corn grain yields and moisture contents differed among hybrids in both years, these differences were similar across all harvest dates. Kernel weights differed among hybrids but were consistent across harvest dates within each hybrid. Our results show stable dry matter following maturity and do not support the need for early harvest and the associated energy expense for grain drying. Research QuestionSome agronomists suggest that corn loses significant amounts of dry matter as it dries in the field after black layer (physiological maturity or R6). Many farmers agree with this suggestion and have documented yield losses associated with delayed harvest. If large dry matter losses occur during field drydown, it may be more cost effective to dry with artificial heat. We conducted a preliminary study in October 1995 and more detailed studies in 1996 and 1997 to determine whether corn kernels lose dry matter as they air dry. Literature SummaryAn October 1995 article in the popular farm press suggested that corn dry matter decreased 1% for every percentage loss in grain moisture after R6 as corn dried in the field. The dry matter loss reportedly was hybrid specific and possibly due to seed respiration. This observation was based on research conducted at Purdue University with three hybrids over 4 yr. All hybrids tested had significant dry matter losses in 3 of the 4 yr. A report of similar observations from farmers and agronomists appeared in 1984 in another popular farm press magazine. Several research reports document kernel weight and yields after R6. No changes in kernel dry weight were observed following R6 in most of the studies. However, in one report, four of 18 hybrids in one study and five of 42 hybrids in another study had changes in kernel dry matter after R6 as corn dried from 35% to about 15% grain moisture. Of the hybrids with dry matter changes after R6, some had increased dry matter and some had decreased dry matter. But, these dry matter changes were not consistent over years. Seed respiration is cited as a possible cause for the reported large dry matter losses following R6. Respiration rates are greatest when grain moisture is near 50% and decrease to a minimal level as grain dries to 15.5%. These dry matter losses increase with greater temperatures and with greater mechanical damage to kernels. But, with good kernel quality and typical fall temperatures in the corn belt (50 to 65°F), it would take an estimated 25 to 50 d for 1% dry matter loss to occur from respiration. This is far less than the 1% dry matter loss reported for every percentage moisture loss after R6. Study DescriptionMost procedures are listed in Table 1. Other procedures were as follows: (i) Kernel handling: On each harvest date for the laboratory and the field dry-down/hand harvest methods, 100 kernels from the middle of two ears per plot were shelled by hand, weighed (wet weight), and oven-dried for 3 d at 194°F before re-weighing to determine dry weight. Percentage moisture was calculated as: ([wet weight − dry weight] ÷ wet weight) × 100. To determine kernel weights in the field drydown/machine harvest method, two 100-kernel grain samples were obtained per subplot for moisture and kernel weight determination and then processed like the hand-harvested samples, (ii) Harvest losses from dropped ears and kernels were measured and used to adjust yields. Applied QuestionsWas corn yield reduced or did corn kernels lose dry matter during drying after R6? No. In 1995 kernel dry weights were not affected by either date of harvest or by the storage environment. Kernel weights differed among hybrids in both 1996 and 1997 but within a hybrid were consistent across harvest dates. Similarly, grain yield obtained from the machine-harvested plots, when adjusted for dropped kernels and ears, did not change over the eight harvest dates. We studied a total of nine drying environments/harvest method combinations with six hybrids over 3 yr. We have found no evidence of kernel dry matter loss following physiological maturity. Why do our results differ from that of other reports? In 1997, we included the Pioneer hybrid 3245 hybrid from the Purdue study with the highest dry matter loss (1.3% for every percentage decrease in moisture). We did not measure any dry matter loss in this hybrid. The Purdue scientists used whole-ear samples. We sampled 100 kernels from the middle part of the ears to monitor kernel weights. We also sub-sampled from the tip and butt ends of two hybrids to see if kernel weight loss occurred at those positions. It did not. The differences in conclusions between our study and that from Purdue are probably because of differences in grain moisture determination procedures. In the Purdue study, grain moisture was estimated with an electronic moisture meter. Moisture meters are often less accurate at moisture contents above 25%. We used oven-dry weights. Differences between our study and reports from farmers may be in a failure on their part to account for field losses or differences in the way grain moisture was estimated. RecommendationWe recommend that farmers monitor individual corn hybrids and fields for grain moisture, stalk quality, and ear retention following R6. Harvest schedules should depend on these variables rather than on concerns of dry matter loss. Our results show stable grain dry matter following maturity and do not support the need for early harvest and the associated energy expense for grain drying. Table 1Hybrids, number of harvest dates, drying environments/harvest methods, and variables measured. University of Nebraska South Central Research and Extension Center, Clay Center, 1995–1997. Number ofDrydownharvestenvironment/VariablesYearHybridsdatesHarvest methodmonitored1995Pioneer hybrid 3225Nine1) Lab table/HandKernel weight2) Lab chamber/Hand3) Field/Hand1996Ciba hybrids:Eight1) Lab table/HandKernel weight Max 212) Field/HandGrain yield 43943) Field/Machine Max 454 4494Pioneer hybrid 32251997Ciba hybrids:Eight1) Lab table/Hand Max 212) Field/HandKernel weight 43943) Field/MachineGrain Yield Max 454 4494Pioneer hybrids: 3225 3245