Estimating corn yields

I was on our weekly agron­omy con­fer­ence call Mon­day morn­ing and Jim Noel, NOAA mete­o­rol­o­gist, told us that weather fore­cast­ers are call­ing for a shift in the weather from wet­ter than aver­age like we had this spring and early sum­mer, to drier than aver­age. That after­noon we got 1.5 inches of rain in Ostran­der. It was a lit­tle funny at the time, but as I drive around the county and the state there is no doubt that a drier weather pat­tern did kick in around late June. Noel says that fore­cast­ers are pre­dict­ing that this type of weather pat­tern will likely con­tinue into August as well. Fore­cast­ers are not pre­dict­ing a drought but are say­ing that the rain­fall will aver­age at or below normal.

This has been a year that really tests a farmer’s abil­ity, and I have to say Delaware County farm­ers have done a great job. Even with the erratic spring weather pat­tern. The corn, while uneven in places, looks very good. The warm weather has allowed a growth explo­sion in many fields. Keep in mind that when corn is at this stage of growth and under favor­able grow­ing con­di­tions plants can grow nearly three inches per day. Around the county I have seen a lot of dif­fer­ence in corn size. Some corn is start­ing to tas­sel but in the same row, other plants will be much dif­fer­ent in size. Farm­ers need to assess how much of the uneven height is due to uneven emer­gence. Although some of the vari­abil­ity in plant height can be related to uneven emer­gence, plant height is not a reli­able indi­ca­tor of plant growth stage in corn. In some fields that show vari­abil­ity in plant height, tall and short plants may actu­ally be at fairly sim­i­lar stages of growth based on leaf collars.

Peter Thomi­son, exten­sion spe­cial­ist at OSU Exten­sion Hor­ti­cul­ture and Crop Sci­ence, says the ques­tion is what impact will vari­abil­ity in devel­op­ment have on crop yields? It’s been well doc­u­mented that uneven emer­gence affects crop per­for­mance because com­pe­ti­tion from larger, early emerg­ing plants decreases the yield from smaller, later emerg­ing plants. Accord­ing to one pop­u­lar rule of thumb, if two neigh­bor­ing plants dif­fer by two or more leaves, the younger plant will almost always be bar­ren or pro­duce a worth­less type nub­bin ear. Sev­eral stud­ies have been con­ducted to deter­mine how later emerg­ing plants impact yield within a field of nor­mal emerg­ing corn.

Research in Ontario indi­cated that when 17 per­cent of the plants are delayed in emer­gence by two leaves, over­all yield was reduced 4 per­cent; when delayed by four leaves, 8 per­cent yield losses were observed. Plants neigh­bor­ing late emerg­ing plants only par­tially off­set yield losses. Illi­nois and Wis­con­sin research con­sid­ered the response of corn when 25, 50, or 75 per­cent of the plants were planted either 10 or 21 days after the orig­i­nal plant­ing date. Over­all, grain yields were reduced 6 to 7 per­cent by a delayed plant­ing of 10 days regard­less of the per­cent­age of plants delayed.

How­ever, when plant­ing was delayed 21 days, yields were reduced 10 per­cent when 25 per­cent of the plants were delayed, 20 per­cent when 50 per­cent were delayed, and 23 per­cent when 75 per­cent of the plants were delayed. In a Min­nesota study, corn planted nor­mally was com­pared to that where half of the seeds were planted either 7 or 14 days later. Nor­mal plants had larger stalks, more tillers, longer ears, more ears, fewer bar­ren plants, and more grain per plant than late plants. Yields were reduced more the longer the delay.

Hope­fully this will give you some guid­ance when esti­mat­ing corn yields this fall. Things look good con­sid­er­ing the spring we had but we have a long way to go.

Rob Leeds is an OSU Exten­sion Edu­ca­tor for Agriculture/NR.

Posted by Rob Leeds on Jul 16 2011. You can follow any responses to this entry through the RSS Feed. Comments can be made below.