How to achieve top maize yields

By Raewyn Densley

Professor Fred Below, a maize expert, said getting the prerequisites right before focusing on seven factors can help farmers achieve high crop yields.

Below is professor of crop physiology in the crop sciences department at the University of Illinois.

He and his team at the university’s crop physiology laboratory research the physiology and biochemistry of high-yield maize. They are focused on helping growers make on-farm management decisions that sustainably produce high yielding crops.

Unfortunately, Below’s arrival in New Zealand coincided with Cyclone Gabrielle’s, resulting in the planned field day being changed to an online event, but not before about 60 growers and industry representatives had made their way to the Mystery Creek venue.

Average USA maize yields go up and down depending on the weather conditions. However, on average, maize grain yield increases about 1t/ha every seven or eight years, mainly due to improvements in crop management, but also to maize hybrid genetics.

However, Below’s two presentations didn’t focus on the average maize grower. They were pitched at how growers might achieve top yields, specifically a 19t/ha maize grain crop.

“It’s not about what’s possible now,” Below said. “In research we need to look down the road as to what we might be able to achieve.”

Yields of this level may appear unrealistic for many growers. Below opened his presentation by introducing USA maize grain grower Herman Warsaw of Illinois who set a world record of 23t/ha maize grain in 1985. In Below’s first year as a University of Illinois professor, he visited Warsaw’s farm and saw first hand research plots that produced 19.7t/ha maize grain. Warsaw achieved this by having high soil fertility levels, planting a high population in slightly narrower rows, matching the hybrid to his system and paying high attention to detail.

Below stressed that getting a number of crucial requirements right was the starting point for achieving high maize yields. These included having good soil structure and drainage, controlling weeds, pests and diseases and having proper soil pH and adequate levels of potassium (K) and phosphorus (P) based on soil tests.

After the basics were in place, Below ranked seven factors that could impact maize yield (Table 1).

He said the higher a farmer was on the list, the bigger the impact on the things below him. For example, the availability of nitrogen [N] was greatly influenced by the weather.

“The weather dictates when you can plant and the weather after that determines the success of the crop. You are way better to plant when the weather is good for uniform, even emergence.”

While NZ’s temperate climate is seen as ideal for maize growing, the penalty associated with hot nights was a timely reminder for growers facing the effects of climate change.

“Every night during grain fill that the temperature stays above 23C results in a 62kg/ha loss in grain yield.”

Below stressed the importance of good crop nutrition which took into consideration crop requirements for key micronutrients, as well as macronutrients including N, P, K and sulphur.

“A micronutrient is a macro problem if it limits yield.”

To ensure adequate nutrition for a high-yielding crop, Below believed that the form, rate, timing and placement of nutrients was important.

His research showed that in environments with high soil N levels, split applications of N increased crop yields.

In the USA, under warmer growing temperatures, maize needs more than 8kg N/hectare a day for 21 days prior to flowering. Required N will not be as much on a daily basis, but the number of days of high demand will be longer under NZ’s temperate growing conditions.

Nutrient placement was also critical because while maize roots grow to great depth, they only spread 15-20 cm horizontally.

“Fertiliser placement is important because maize roots do not cross the row.”

Below said that in the USA, Y-DROP application of liquid N to maize was gaining popularity. The method allows for the N to be placed within a few centimetres of the maize stalks, which means nearly 80% of the root mass is in the fertiliser application zone.

Strip till, a system where only the narrow strip where the maize seed will be planted is cultivated, was growing in popularity. Below believed that one of its key advantages was the banding of the fertiliser in the strip below the seed allowing better plant access to nutrients.

Maize hybrid selection was in third place in Below’s ranking system. His Illinois yield potential trials carried out using three sites, 32 hybrids and six factorial levels of management continued to demonstrate that “not all hybrids are created equal”.

Below said the best hybrid to plant is usually the newest one. He also reminded growers not to buy seed on price as “you get what you pay for”.

Short stature an option

Below urged the audience to keep an eye out for short stature maize hybrids.

“Maize is the last major grain plant to be dwarfed, and short stature maize delivers management and physiological advantages compared with conventional tall maize hybrids.”

Plants have a thicker lower stem and are better able to withstand wind, the lower height makes it a lot easier to ground spray at later growth stages. There is also less residue after grain harvest which is an advantage for reduced tillage systems.

He said it may not be so good for maize silage, but when growing short stature varieties grain there are advantages when windy.

According to Below, keeping the plant population up is a key factor for achieving high maize yields.

“Grain yield is determined by the number of plants per hectare, the number of maize kernels per plant and the weight of each kernel,” he said. “The one which growers have the most control over is plants per hectare.”

In the USA average seeding rates for grain crops have risen about 900 plants a hectare each year since the 1960s. Modern hybrids can perform well even at high planting densities. However, as plant population increases, root size decreases meaning plants are more susceptible to competition from neighbouring plants.

“There’s about a 1% decrease in root mass per 1000 plant increase in population.”

Below likened the competition plants face within the row to that of people around the dinner table.

“You don’t want to sit too close to someone at the dinner table, you want some elbow room and maize plants are the same.”

He predicted that recommended planting populations would continue to rise and eventually reach a point where the increased competition between plants within a row limited yield increase. His solution to reducing competition between plants was to reduce row spacing. Narrow rows allowed the crop to intercept more light, there was less competition between plants and the size of each plant’s roots increased when compared to the same plant population planted in conventionally spaced rows.

While high plant population was a fundamental of higher yields, Below was quick to remind the audience that you couldn’t look at any one factor in isolation. The smaller root system of each individual plant further heightened the need to get the source, rate, time and placement of crop nutrients correct.

US research showed that crop rotation could impact maize yields both positively and negatively. Maize crops following a legume generally had higher yields. Crop after a crop of Maize suffered a yield penalty. Below recommended local maize growers evaluate the impact of crop rotations and winter options on yields.

He likened tillage system preference to religion where followers tended to vehemently back their preferred option. His research showed tillage systems that preserved crop residues could have a positive impact on maize grain crop yields.

The final factor, which is gaining grower interest globally, is the use of biological products to enhance maize yield by relieving plant stress and/or improving nutrient availability. Biologicals commercially available in the USA included seed treatments, products that were applied in-furrow with the starter fertiliser, foliar products that were applied with the post-emergence herbicide or at the reproductive stage, along with fungicide or insecticide or to crop residues.

A number of different biological products showing promise in the USA focused on taking N gas from the air and converting it into plant-available forms that could be used by the plant for growth and yield. These products had a low carbon footprint and no or limited nitrous oxide emission if produced directly in the root rhizosphere or as endophytes within the plant.

Below’s advice on the use of biologicals was “be sceptical but willing to try”.

“Know what they are supposed to do and whether you need that done.”

• Raewyn Densley is an ag consultant.