Evaluation of Double Crop Corn in Eastern Virginia

Crop and Soil Environmental News, January 1998

H. Behl, research specialist;
E. Bender, research associate;
D. Brann, Extension specialist, grains;
D. Moore, Extension agent, Middlesex County;
L. Barrack, research specialist

Double cropping corn for silage after small grain silage is practiced on a number of farms in Virginia. Double cropping corn for grain after small grain harvest for grain is not currently practiced. This research was initiated to ultimately develop a cropping system for continuous double cropping. This system may be especially well-suited on soils that are too droughty to produce only a summer crop profitably. The cropping system will emphasize well-managed wheat, barley, or some other winter annual.

Corn hybrids with a relative maturity from 75 to 115 days were planted at Corbin Hall near Saluda and on the Eastern Virginia AREC near Warsaw, Virginia at the time of barley harvest. The plots at Warsaw were planted conventional tillage whereas the plots at Corbin Hall were planted no-till. Nitrogen at 125 lb N/acre was applied at planting at Corbin Hall and 150 lb N/acre at Warsaw. No insecticide was applied.

Amazingly, corn was 5-6 inches tall two weeks after planting, 5 feet tall one month after planting, and beginning to tassel 55-65 days after planting. Excellent quality corn grain yields of 100 to 150 bu/acre were obtained both non-irrigated and with supplemental irrigation.

Corn hybrids with a relative maturity less than 90 days produced nearly 50% less yield than hybrids in the 100-115 day relative maturity range. Fortunately, corn hybrids with a relatively maturity of 100-115 days will be less than 25% grain moisture by mid-October even when planted in mid-June. We will not have to plant extremely early corn hybrids to fit double crop corn into a continuous double crop system.

When planted in mid-June in eastern Virginia the 91-105 day hybrids may yield similar to 106-115 day hybrids over years because the 91-105 day hybrids initiate tasseling during longer days. The ultimate yield-determining factor will be rainfall and available moisture at silking and tasseling. It may be advisable to plant at least two hybrids with different maturities to spread risk of drought at silking.

The study at Warsaw compared corn with Group IV soybeans (Table 29). The best corn hybrids yielded 122-126 bu/acre, whereas the two soybean varieties averaged 37 bu/acre, and the best grain sorghum averaged 141 bu/acre. At current prices, the net profits from the above three species would be similar. Two factors need to be considered. Double crop soybeans work extremely well and our goal is not to beat soybeans but to add another alternative for long term rotations. Second, the grain sorghum did extremely well this year and was sufficiently dry to harvest due to low rainfall and high temperatures for two weeks prior to harvest. Grain sorghum is normally slow to dry in the field and cannot be harvested and dried above 20% moisture.

European corn borer pressure was low at these locations this year. Corn earworm pressure was relatively low but the number of damaged ears at Corbin Hall was lower when comparing iso-lines such as N6800 with N6800 Bt(11). It is also interesting to note that the top 5 hybrids non-irrigated as well as supplementally irrigated had the Bt gene incorporated.

Further research must be conducted to evaluate the importance of insect resistance in selecting corn to be planted double crop in eastern Virginia.

In summary, 1997 results showed that double crop corn behind barley can be successful. The degree to which it is successful long term will be determined by further research and producer experience.

Table 27. Double crop study at Corbin Hall in 1997 - Non-Irrigated.

Brand/ Company	Hybrid	Yield bu/A	Relative Maturity	Moist %	Test Wt lb/bu	Plants/A	%CEW Damaged Ears
NK	N6800-Bt(11)	125	112	20.0	55.9	26136	17
PIONEER	35N05-Bt	118	107	18.7	57.0	24321	23
NK	N4640-Bt(11)	113	106	16.9	55.4	24684	17
PIONEER	33Y09-Bt	113	113	20.9	54.5	25501	44
PIONEER	33V08-Bt	112	110	20.5	56.0	25229	38
NK	N4242-Bt(11)	111	104	17.5	56.3	24049	15
MYCOGEN	7559	107	115	19.6	54.0	24321	79
NK	N4640	106	106	16.8	54.5	25501	59
NK	N6800	106	112	20.3	56.0	23323	63
NK	N7639-Bt(11)	105	112	22.9	54.0	25592	20
PIONEER	36K27-Bt	105	102	16.2	53.6	22778	28
MYCOGEN	2598	104	105	18.4	54.0	23323	62
AUGUSTA	2067	101	90	18.2	56.7	21054	75
NK	N4242	97	104	17.5	55.3	23777	48
MYCOGEN	2382	95	94	16.6	55.0	23141	25
MYCOGEN	2362	93	93	17.0	56.9	22325	34
DEKALB	DK546	90	104	17.8	55.2	22506	65
DEKALB	DK446	88	94	16.1	54.3	23504	48
PIONEER	3905	87	87	17.0	56.1	23232	59
PIONEER	3984	57	75	18.7	58.8	23323	43
Corn Average		102		18.4	55.5	23881	43
LSD (0.05)		18		0.8	1.1	2387	24
Site was planted June 10 and harvested October 21, 1997. Leaf damage, European corn borer stalk and ear shank ratings, and number of ECB larvae evaluations were made on each hybrid by Dr. Rob Youngman, Extension Entomologist at VA Tech. There was little to no damage in any plots. The corn ear worm ratings were also made by Dr. Youngman. Sorghum at this site ranged in yield from 70 to 80 bu/acre.

Table 28. Double Crop Study at Corbin Hall in 1997 - Irrigated

Brand/ Company	Hybrid	Yield bu/A	Relative Maturity	Moist %	Test Wt lb/bu	Plants/A
PIONEER	35N05-Bt	150	107	21.0	55.3	26894
PIONEER	33Y09-Bt	138	113	21.7	52.7	25268
PIONEER	33V08-Bt	130	110	23.1	54.0	24834
NK	N6800-Bt(11)	125	112	22.9	53.4	25378
PIONEER	36K27-Bt	122	102	17.9	53.4	23863
NK	N6800	119	112	22.8	53.3	25378
DEKALB	DK446	114	94	19.4	53.1	22190
NK	N4640-Bt(11)	113	106	19.4	53.2	24487
AUGUSTA	2067	108	90	20.2	53.9	24810
NK	N7639-Bt(11)	105	112	24.2	53.2	24053
MYCOGEN	2598	102	105	19.6	52.8	26325
MYCOGEN	2362	102	93	18.1	56.1	22956
NK	N4242-Bt(11)	99	104	20.2	55.6	24242
MYCOGEN	2382	99	94	18.4	53.8	24297
PIONEER	3905	98	87	19.3	55.3	25757
NK	N4640	94	106	19.4	52.9	22159
MYCOGEN	7559	89	115	25.6	51.7	22656
DEKALB	DK546	82	104	19.0	54.1	20873
NK	N4242	79	104	20.2	52.9	22474
PIONEER	3984	76	75	19.1	58.4	24053
Corn Average		108		20.6	54.0	24147
LSD		28		2.1	2.0	3919
Site was planted June 10 and harvested October 21, 1997. Irrigation included 0.75" applied three times during the growing season. There was one storm near the end of July that provided 3" of rain. Complete rainfall data is unavailable. The relatively high LSD is related to the fact that there was space for only two replications in the irrigated area.

Table 29. Double crop study at Warsaw in 1997 - Non-Irrigated

Hybrid/ Line	Yield bu/A	Relative Maturity	Moist %	Days To Silk	Days To Tassel	Test Wt lb/bu
Asgrow AG4341	39	Group IV	12.2
FFR-439	36	Group IV	12.3
Soybean Average	37		12.3
LSD	7		0.2
P33V08-Bt	126	110	17.2	59	58	58.6
P36K27-Bt	122	102	15.4	57	53	53.4
P35N05-Bt	108	107	15.3	58	54	60.0
N7639-Bt(11)	92	112	15.4	59	55	60.0
N4242	91	104	11.7	53	52	57.4
N4242-Bt(11)	79	104	13.3	55	51	59.2
Corn Average	103		14.7	57	54	58.1
LSD	21		3.4	1	3	3.0
P8446-GAUCHO	141	Medium	11.2			56.7
P8699	88	Very Early	10.1			53.9
Sorghum Average	115		10.6			55.3
LSD	21		0.2			5.3
European corn borer ratings on the corn plots were made by Dr. Rod Youngman, Extension Entomologist at VA Tech. There were essentially no corn earworms or European corn borers present in these plots. Site was planted June 17 and harvested October 14, 1997. Rainfall data for this site is as follows:

June 14 26 27 Total	0.71" 0.32" 0.50" 1.53"	August 4 5 17 20 28 Total	0.25" 0.02" 0.03" 1.26" 0.76" 2.32"	(98 F) (99 F)
July 2 10 17 22 23 24 29 Total	0.14" 0.43" 0.04" 1.10" 0.74" 3.22" 0.12" 5.79"	September 9 10 11 13 24 28 Total	0.12" 0.03" 0.37" 0.42" 0.40" 0.05" 2.39"
		October 1-14	0.02"

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