Planting Soybeans Behind The Flood

For those who had planted soybeans and lost an established crop, a completely different production scenario now exists.

For those who had not planted, intended planting date will certainly be delayed beyond the intended planting time, and this too will completely change intended management practices.

Two basic questions come into play regarding planting soybeans in this situation.

1. Can soybeans be planted behind the flood with a reasonable expectation of harvesting a profitable crop?


2. What management practices can be used to ensure the maximum possible yield from an ultra-late planted soybean crop?


 

The answer to the first question is a qualified YES, especially with high commodity prices. However, yield potential will be greatly reduced to estimated maximums of 25 to 30 bu/acre in nonirrigated plantings and 40 to 45 bu/acre in irrigated plantings. These estimated maximums assume a high level of management and average or above-average rainfall for the remainder of the growing season.

To answer the second question, the first consideration is to determine the estimated length of growing season that can be expected based on projected planting dates behind the flood coupled with estimated first fall frost date.

Data in the below table provide the estimated length of the growing season at five Mississippi locations based on planting dates ranging from July 1 to August 10 and the estimated date of the first fall frost (36 deg.). Keep in mind that a first fall freeze (32 deg.) is estimated to occur 10 days to 2 weeks later than the estimated first frost dates shown for each location. Also keep in mind that, even though a killing frost may not occur on the dates shown in the table, temperatures at this level will likely signal the end of any appreciable plant activity.

The following narrative is based on using the 50% first frost date (an earlier date than the one shown is expected to occur in 5 years out of 10) at these locations as the projected end of a growing season.

• For a July 1 planting date, the estimated growing season length exceeds 118 days at all five locations. Therefore, MG IV through VI varieties can be planted without fear of frost injury.


• For a July 20 planting date, the estimated growing season length is between 99 and 110 days. MG IV through V varieties should be near or have reached R8 or full maturity by this time. MG VI varieties are probably a safe selection at the southernmost locations in the table.


• For an August 10 planting date, the estimated growing season length is estimated to be less than 90 days at all locations. MG IV varieties should have safely reached R8 by this time.


• I am not aware of any ultra-late plantings where maturity dates were recorded. The information above should only be used as a guide. Deciding which MG’s varieties should be chosen from is an arbitrary decision.


 

Most available information leads to the selection of MG VI varieties for greatest yields when planting from mid-June through about mid-July since they have the potential for the longest fulfilled growing season.

When planting after mid-July, MG V varieties may be the best choice since they are likely to fulfill their maximum potential growing season length before the estimated 50% frost date. Late MG IV indeterminate varieties can be planted this late, but they will be short at maturity.

The second consideration is to delineate known or perceived management practices that should be used in ultra-late plantings to provide the best opportunity for success. The following are management considerations that I believe are safe to assume.

• Do not till prior to planting. This will result in the earliest possible planting following receding flood waters, possibly planting before weed emergence, and conservation of soil moisture.


• Plant in narrow rows, preferably less than 20 inches. Forming a crop canopy as quickly as possible in these plantings is critical for success.


• Use a broad-spectrum seed treatment and inoculate seed with nitrogen-fixing bacteria.  See the article by Tom Allen for a list of seed treatment and inoculant products.


• Do not apply starter nitrogen fertilizer. Inoculants are cheaper.


• Ensure a weed-free seedbed at planting. Any early-season competition from weeds will be more critical in ultra-late plantings. A reasonable option is to apply a tankmix of a burndown/residual herbicide combination (see following point).


• Using pre-emergence herbicides that require rainfall for activation will be high-risk given the low probability of July and August rain. If pre-emergence herbicides are used, be sure to match the herbicide rate with the soil texture to prevent any early-season stunting.


• Prevent any early-season weed competition with the soybean crop after emergence. This means more intense scouting for weed emergence and more timely post-emergence herbicide applications following soybean emergence if residual herbicides are not used or are not activated by rainfall or irrigation.


• Scout for late-season insects and diseases (especially rust). Applications of curative and/or preventive pesticides will be required to protect yield. A thorough treatment of pest management practices for ultra-late plantings is provided in MSU publication 2680.


• Finally, remember that nonirrigated yields will be low from these plantings and may not be profitable if expensive inputs for weed and pest control are necessary.


 

A Farm Policy Brief authored by Corey Miller and Keith Coble of MSU-Ag. Econ. discusses the prevented planting provisions of flood insurance. This article is a summary of “Prevented Planting Insurance Provisions–Flood” published by the USDA-RMA. It offers valuable insights into how crop insurance is affected by planting that is affected by flooding.

A recent publication entitled “After the Flood: Row Crop Replanting” by the MSU Extension Service offers many helpful tips for managing soybeans that are planted late following receding flood waters.



























































































































































 

Length of growing season based on planting date and first fall frost (36 degrees) date at the 10%, 50%, and 90% probability levels.
	Planting date
Probability and date#	July 1	July 10	July 20	Aug. 1	Aug. 10
Hernando
10% (Oct. 12)	103	94	84	72	63
50% (Oct. 27)	118	109	99	87	78
90% (Nov. 11)	133	124	114	102	93
Greenville
10% (Oct. 18)	109	100	90	78	69
50% (Nov. 2)	124	115	105	93	84
90% (Nov. 18)	140	131	121	109	100
Rolling Fork
10% (Oct. 12)	103	94	84	72	63
50% (Oct. 31)	122	113	103	91	82
90% (Nov. 20)	142	133	123	111	102
Vicksburg
10% (Oct. 17)	108	99	89	77	68
50% (Nov. 6)	128	119	109	97	88
90% (Nov. 25)	147	138	128	116	107
Natchez
10% (Oct. 20)	111	102	92	80	71
50% (Nov. 7)	129	120	110	98	89
90% (Nov. 25)	147	138	128	116	107
#The probability levels are the probability of an earlier date of occurrence in the fall at each location than shown in parenthesis. That is, at the 90% probability level, an earlier date than the one shown is expected to occur in 9 years out of 10; at the 50% probability level, an earlier date than the one shown is expected to occur in 5 years out of 10; at the 10% probability level, an earlier date than the one shown for each temperature is expected to occur in only 1year out of 10.

 larryheatherly@bellsouth.net