No Crops are Alike or are They?

Friday, February 10, 2023

By Paul Hermans

To the average city folk, all crops are the same. They need sun, water, plus nutrients to grow.

When we look more closely at corn and soybeans, yes, it is true they need all of this, but at different times of the year. Each crop is unique in their vegetative and reproductive stages of growth.

This article is the start of a two-part series. This month I will focus on the earlier vegetative stages of corn and soybeans. I will follow up with the second article on the reproductive stages.

I will explore the differences between corn and soybeans, how they grow, and talk about some management tips you can utilize on your farm to increase yields.

Corn has four critical growth stages. They are emergence, V4 to V6, flowering, and grain fill. Soybeans are basically broken down into vegetative and reproductive stages.

When we refer to "V" stages we are taking about vegetative stages in both crops.

Emergence

Corn requires 30 per cent of its seed weight in water absorption to germinate, compared to soybeans, which require 50 per cent. Keep an eye on planting depths as soils dry out, especially for soybeans.

Recent corn studies have shown that "deeper planting depths" of 2 to 2-1/2Ë have better uniformity compared to less than 2" planting depths.

To prove this point, I conducted a "planter goof" demonstration at a showcase plot. We planted corn at various depths. Corn emergence numbers told the story and confirmed that keeping an eye on depth in corn is critical. Even emergence and uniformity in cob size are the main objectives to obtain higher yields.

Soybeans are more sensitive to seed-placed fertilizer than corn, so keep an eye on amount and type of fertilizer being applied along with soil type.

In general, corn compared to soybeans is more affected by cooler soil temperatures. Watch weather patterns and stress-emergence scores of the hybrids you choose for early planting dates.

Stress-emergence scores for corn are critical when planting early or in cooler soils. This is especially true for minimum and/or strip-tillage management practices.

The initial water a crop takes up is important for sound emergence. Keep an eye on weather fronts and avoid a "cold drink" of water for your crops at least six to 12 hours or more after planting. The highest water volume is taken up within the first 30 minutes. If you must push the planting window, planting in the heat of the day and shutting planting operations down before sunset is advisable.

More growers are planting soybeans early, compared to corn. The main reason is because uneven corn has a greater yield-loss potential than soybeans. If we lose 5,000 to 6,000 corn plants from an initial planting rate of 36,000, this is a lot worse off than losing 20,000 to 30,000 soybean plants from an initial planting rate of 165,000.

V2 to V6 stage

Early on in its development (V4 to V6) corn sets the numbers of kernel rows around the ear. Ensuring stresses are minimized at this stage helps with final yield in corn. Adequate fertility up front, especially nitrogen and phosphorus, will promote sound root structures, leading to a solid foundation through-out the summer months.

Excessive moisture in the rooting zone can lead to stresses, reducing kernel rows around the plant.

Look at your cobs over time and think back to "pinch rows" in cobs that went from 16 to 14 rows as an example. The plant is telling you a story about what growth conditions were like at that point in the corn's lifecycle.

Tile drainage is key for uniform moisture and soil temperatures. Just like humans, all crops like consistency. Rapid temperature and/or moisture swings stresses plants, taking away growth potential.

Soybeans are less sensitive at this period. Soybeans go through the "ugly duckling" phase when nodulation starts to take place around V2, when nitrogen can be lacking. Soil pH has a dramatic effect on nodulation as well. Watch soil pH and lime requirements to assist in proper nodulation and other key factors such as weed control and nutrient availability.

Temperature & sunlight

Each of these crops need sun and heat to drive photosynthesis and crop development. It's this energy that drives the accumulation of resources to the seed. All crops and plant life in general have a primary goal to grow and reproduce (make as much seed as they possibly can).

Corn maximizes its growth potential around 30 C. Soybeans prefer it cooler, with temperatures around 24 C. Understandably, you cannot control the temperature, but in some regards you can control water availability through improved soil health management. The more we can provide our crops with available water, the easier the crops can overcome stresses when temperatures exceed 30 C.

For both crops water needs are most critical during reproductive stages. A corn crop uses 50 per cent of its seasonal water during reproductive stages.

During the vegetative stages of corn, corn can move faster or slower through those stages depending on heat unit accumulation.

Earlier planting dates are great to ensure earlier flowering dates. However, as I mentioned above, pushing soil conditions with cold temperature weather patterns can dramatically reduce yield through poor or uneven emergence.

For soybeans, the key to higher yields is to have at least six trifoliates on the plant before it goes into its reproductive phase (R1).

Early planting promotes more nodes, more flowers, and more pods, resulting in more grain yield. Planting date studies conducted in Eastern Ontario have resulted in a three to five-bushel yield response for planting 10 to 14 days earlier. Similar yield gains for earlier-planting soybeans have been seen across different geographies in North America.

Nutrient needs

When corn reaches V8 stage, it grows rapidly until it reaches tassel time (VT). Not many crops can go from knee-high to shoulder-high in a two-week period. Nitrogen uptake through this growth spurt represents about 50 per cent of the total N required to grow the crop. Proper timing, placement, and N-type assist in maximizing yield.

Soybeans maximize phosphorous and potassium uptake in the early reproductive stages.

Expanding our yield horizons in both crops requires keeping an eye on crop removal rates, and replenishing the soil's fertility bank account will make for a great foundation when seeding the next crop.

The maximum potential of any crop is when the seed is still in the bag. Once you open that bag the potential drops off. Setting the stage early on, in the vegetative stages with optimal planting depth, ideal planting dates, good fertility, drainage and soil pH, will ensure your corn and soybean crops enter the reproductive stages with the highest yield potential possible.

In my next article I will review tips on how to manage crops during these reproductive stages and what the key stages are for both corn and soybeans.

Until then, you can start thinking about what different management practices you can incorporate to get higher yields in 2023! BF