One of the most common questions we get from growers this time of year is what seeding rate should be used in their crops. The amount of seed used to plant an acre is more important than in the past since cost of the seed is much higher now since they perform a dual role in establishing a stand of seedlings and carrying technology traits.
Even though the delivery of technology traits is important, the population of plants is just as importance today as it has ever been. Plant populations influence the way plants develop, the way they react to sunlight, and in many cases the way weeds, diseases, and insects affect the crop. Populations can be adjusted to fit field conditions in relation to soil type, yield goals and production practices of individual growers. A few growers are varying their seeding rates according to predetermined criteria, and I expect this practice will become more common.
We have almost finished planting corn for this year, but we debate the subject of population in this crop every year. The big issue is water so we vary populations significantly based on whether the field is irrigated. Seeding rates run the gamut from a low just north of twenty thousand to a high above forty thousand in areas where all the factors are maximized. Only the best soil fertility and irrigation practices will justify the high end numbers for corn, but yields can justify the efforts in most years.
In nonirrigated fields our best populations are usually in the upper twenty thousand range, but the more aggressive growers go just above thirty thousand in an effort to be ready when nature provides plenty of water.
Cotton may be the most difficult crop we grow in which to settle on the correct plant population. In the old days cotton farmers commonly planted over 100,000 seed per acre. After emergence the stand was “chopped” down to as low as fifteen thousand so that plants would receive plenty of sunlight to promote fruiting and early maturity. Today we do our best to plant the right amount of seed and at the desired spacing so as to conserve seed that are very expensive.
Growers commonly plant forty to fifty thousand seed per acre in the hope that a stand of at least thirty five thousand healthy plants will be achieved on each “planted” acre. Some producers utilize a skip row planting pattern as another means of conserving seed, especially on the most productive soils where plants can take advantage of the unplanted row space.
In a spacing and population study I did in 2005 I planted from one to five seed per foot of row in both solid and skip row patterns. The stand was fairly uniform and yields were very similar in all of the treatments, but as we all know 2005 was the year we had two hurricanes with one named Katrina and one named Rita.
These two storms devastated crops regardless of population, but they taught me that very low populations of cotton cannot deal with wind since the plants were like small trees. Limbs loaded with bolls were torn off and the low populations could not be salvaged with a picker while the higher populations were harvested in relatively good condition.
Soybeans are a real head-scratcher with regard to population. Research has shown that yields change very little with populations from around 70 to around 140 thousand plants per acre, with little regard to row spacing. It has been shown that somewhat higher populations shade the soil more quickly and suppress weeds, but this same higher populations may develop disease and insect problems earlier in their maturity than the lower populations because of the influence of sunlight.
I commonly suggest that growers plant soybeans with the goal of achieving around 100,000 plants per acre since this seems to be a fairly happy median level for most situations.
Every year may produce differing results because of differing weather, planting dates, varieties, and other factors. I expect the debate over plant population will continue well into the future without a firm conclusion, but then that’s farming.
Thanks for your time.