When Should You Replant?

Nearly every grower must decide whether to replant a sparse stand at some time, and it's one of the tougher decisions a producer has to make.

Part of the difficulty stems from trying to predict how stand density and yield will be affected by a later planting date and changing conditions, says Bill Wiebold, agronomist, and Ray Massey, ag economist, both with the University of Missouri Extension. These two specialists have written a guide (G4091) to making replant decisions, which is available at www.muextension.missouri.edu.

“I usually make replanting decisions on the basis of plant population,” says David Durham, corn and soybean producer at Hardin, MO. “I want at least 140,000 soybean plants and try to maintain a minimum of 70% of a normal corn stand. We often pull the planter into the field to replant just those spots where the stand is most sparse.”

Ben Thompson, Osage City, KS, agrees that getting a good estimate of the stand is basic. “We take a stand count and then decide whether replanting is worth the extra cost,” he says. “Soybeans in a sparse stand will compensate some, but we definitely replant when the stand is 70,000 plants/acre or less.

“We don't like to replant, and we haven't done much of it,” Thompson adds. “We don't plant initially unless we're 98% sure of getting a good stand. We want to make sure it works right the first time.”

Wiebold and Massey recommend following a step-by-step procedure to estimate dollar gain or loss from replanting. Study the field and do an analysis of yield potential, following these steps:

1. What's the cause of the sparse stand?

2. Determine the stand's density and condition, and estimate the yield potential

3. Estimate the expected gross revenue from the sparse stand.

4. Estimate the cost to replant: seed, fuel and machinery, pesticides and interest on loans associated with replanting.

5. Estimate the yield potential and revenue from a replanted stand.

6. Will the decision whether or not to replant pay for itself?

Finding out why is an essential first step, say Wiebold and Massey. Determining the cause of a sparse stand is important because the same thing may happen when you replant, unless the cause is identified and corrected. Poor seed quality, herbicide injury and insect or disease injury can decrease the stand the second go-round.

In most cases — especially with corn — planting into an existing sparse stand is not a good idea because plants of uneven sizes and maturity perform poorly. An exception might be spots of low plant population in a field, which could be replanted as Durham notes.

If you need to do general replanting, you can kill out the existing poor stand with herbicides or tillage. Replanting without tillage saves time and soil moisture and doesn't dilute existing pre-emergence herbicides.

As Thompson says, a fairly accurate count of the live plants is needed to determine the potential yield of a sparse stand. The number of areas to be sampled depends on the extent and uniformity of the damage. With nearly uniform damage, fewer areas of the field need to be sampled.

The easiest way to estimate the population of a sparse stand is to count plants in a measured area. For example, with row crops, you can simplify the calculation by counting plants in a length of row equal to 1/1,000 of an acre, as in the table below:

Row Width	Length Of RowEqual To 1/1000 Acre
30 in.	17 ft., 5 in.
20 in.	26 ft., 2 in.
15 in.	34 ft., 10 in.

For solid-seeded (drilled) soybeans, you can use the “hula hoop” method to estimate the remaining population.

Once you have determined how many healthy plants remain in a damaged stand (and what percent of a normal stand this represents), you can estimate the stand's yield potential. The decision to replant can be based on what you expect that yield to be worth at harvest. Keep in mind that delayed planting usually will decrease yield, although the amount of decrease is tough to predict.

The yield from a replanted stand usually would be worth more than that from the sparse stand, but you need to weigh the cost of replanting — which may exceed the value of the additional yield from replanting.

Estimate only those extra costs that would be involved in replanting — seed, fuel, labor and machinery. Fertilizer, chemical and other expenses already made in production are considered “sunk” costs and shouldn't influence your decision.

It's a safe bet that crop input prices will be higher this spring — especially fuel. But how much will higher costs influence replanting decisions? “Some, but not much,” says Durham. “The value of having a good stand offsets some higher costs.”

Hula Hoop Method

	Diameter Of Hoop
	30 in.	32 in.	34 in.	36 in.	38 in.
Number Of Plants In Hoop		Thousands Of Plants/Acre
2	18	15	14	12	11
4	35	31	28	25	22
6	53	47	41	37	33
8	71	62	55	49	44
10	89	75	69	62	55
12	107	94	83	74	66