Normally this time of year farmers in our area are getting antsy waiting to start planting corn. So, when should corn be planted? The soil temperature is the determining factor on when to start planting. Corn can be planted as soon as temperature and moisture become favorable for seed germination and seedling growth. Soil temperature in the seed zone should be 55F or greater before planting. Corn seed will sprout slowly at 55F while germination is prompt at 60F. Delay planting if cold weather drops soil temperatures below 55F at the two-inch level. However, if soil temperatures are 55F and higher, and projections are for a warming trend, corn planting can proceed. Extremely early planting introduces a risk to frost or freeze damage and subsequent loss of stands. Usually, as long as the growing point is below ground level, corn can withstand a severe frost or freezing damage without yield reduction. It is best therefore to monitor soil conditions and weather if your desire is to plant as early as possible. Generally it takes corn seed 7 to 12 days to emerge when planted in soils there are 55F.
According to the Georgia automated environmental monitoring network, soil temperature has averaged 55 from March 7 to March 10 at the 2 inch level. Temperatures are just high enough for corn germination, but cooler temperatures are predicted.
March and April are the best months to plant corn. As planting is delayed into the summer, corn yields decline. In general, yields decline at ¾ a bushel per day rising to about 2.5 bushels per day. Studies in Tifton, under irrigation, demonstrate that yields of stress tolerant and disease resistant hybrids are about 50% of normal when planted in late May or early June. Therefore, late planting is very risky with a high degree of failure.
Plant 10% more seed/ac than is necessary to produce the desired plant population for any particular hybrid. This over-planting will leave the harvest plant population at the desired level after a normal stand loss due to uncontrollable factors. Optimum plant populations for dryland production range in general from 18,000 to 20,000. Though greater plant populations would provide higher yields in good rainfall years, the stress of higher plant populations above 20,000 in drier years would significantly increase the risk to yield loss due to plant competition. Conversely, lower plant populations reduce yield potential in years with adequate rainfall.
Irrigated corn requires higher plant population than dryland corn to fully explore the potential of irrigation. Generally 26,000 to 36,000 plants/A are recommended for most intensively grown hybrids. Excessive populations increase seed costs and may reduce yield because of crowding and lodging.
Most farm equipment in Georgia is set to plant in 36″ rows. Wider rows, 38” to 40″ rows usually results in little space between plants within a row. This creates in-row competition for water and nutrients. Studies conducted in corn reveal that yields increase as rows narrow at high plant populations. In a four year study of 20, 30, 36 and twin 36 inch rows, corn yield was 254, 245, 235, and 237 bushels per acre. If twin row spacing is used, it is best to fully disrupt the hard pans beneath both rows. Either adding shanks or using some type of full zone fracturing allows the plants to grow without root restriction. Row widths of 30 to 36 inches are adequate for top yields in Georgia.