Do lower plant populations pay?
Date: 23 May 2016
Every year Pioneer researchers, in New Zealand and internationally, conduct plant population studies to establish the best population for newly released hybrids. Local research has shown that over the last 20 – 25 years maize grain and silage yields have increased at a rate of 100 and 160 kgDM/ha/yr. These results are quite similar to the US. While some of the yield is due to better crop management, 50 - 60 % can be attributed to genetic gains.1
USA research conducted by Dr. Duvick comparing hybrids from different generations (1930s – 2000s) found there were no yield differences between newer (1990s) and older (1930s) hybrids when planted at very low populations (10,000 plants/ha). When planted at higher densities (e.g. 79,000 plants/ha) newer hybrids significantly outperformed older hybrids. This is clear evidence that the yield benefit of newer hybrids is not due to a greater yield potential on a plant basis but rather, a greater ability to withstand stress conditions. Planting an older hybrid at higher populations could result in plant lodging or barrenness whereas newer hybrids tolerate the higher population and produce a very good yield.
It is always tempting to compare a cob/plant planted at a low population density vs. high density (e.g., 75,000 vs. 120,000) and assume the low density crop will produce higher yields due to bigger cobs (Image 1). Always keep in mind that you only have 75,000 of the bigger cobs vs. 120,000 of the smaller cobs. In this example, the grain yield was quite similar though slightly higher for the high population crop (7.7 vs. 7.8 t/ha).
Image 1: Cob size variation between a grain hybrid planted at a high vs a low population
To determine profitability always consider seed and treatment cost vs. the yield gain and the value of the yield in dollar terms.
Optimum population is largely influenced by hybrid and yield environment. High yield potential paddocks require a higher population to maximise yield compared to lower producing paddocks (Figure 1). Preliminary* results from local research are showing that if paddock grain yield potential is 14 - 15 t/ha, yield will increase at a rate of 70 kg per 1,000 extra plants up to 105,000 plants/ha, after which yield begins to drop. For a 10 t/ha potential paddock, yield will only increase at a rate of 12 kg per 1,000 extra plants up to 90,000 plants per ha. This principle can be used to help establish the most profitable population for your growing conditions.
Figure 1: Grain yield response to plant populations at four yield levels. Arrows indicate the optimum population to achieve the highest yield.
There are many factors which will determine the yield of your maize crop. Plant population is one of the few that are under the control of the grower. To maximise yields and profits, always consider your yield potential and then select a population that will produce the highest returns.
For more information please contact your local Pioneer representative.
*Results may vary as data from 2016 harvest becomes available.
1Duvick D.N., 2005. Genetic progress of yield of United States Maize (Zea mays, L). Maydica, 50: 193 – 202.