The objective of this study was to determine the effect of planting density on yield and nutritional composition of corn silage in a 2×-crop rotation system. The study was performed at an 800-cow dairy farm located in south Virginia. Corn was planted in experimental plots within 2 cornfields, one of which was irrigated with a central-pivot irrigating system. Planting densities were 55, 70, 85, and 100 seeds/ha (×1000) in 4 replicates per cornfield (2 fields x 4 densities x 4 replicates = 32 plots). Plots were 12 25-m long rows separated by 76 cm. The irrigated cornfield was watered with 100 mm of water before tasseling. At the early-dent stage of maturity, 10 plants from each plot were cut (15 cm above ground), weighed, chopped, mixed thoroughly, and ensiled in bags for 60 d. Nutritional composition was performed by wet chemistry. The statistical model included the effects of irrigation (I), density (D), the 2-way interaction (I×D), block, and field-by-block interaction. No interactions between irrigation and planting density were observed for any of the variables of interest. Dry matter yield was not affected by planting density. Increasing planting density reduced plant biomass. Planting density did not affect the concentrations of CP, NDF, ADF, ADL, and starch, but tended to affect IVNDFD quadratically. In conclusion, under a double-crop rotation system increasing planting density of corn does not increase DM yield and also does not affect the nutritional composition of corn silage when harvested at an early stage of maturity. Table 1. Effect of corn planting density (plants/ha × 1000) on yield and nutritional quality of corn silage

	Nonirrigated					Irrigated				SEM	P<
	55	70	85	100	55	70	85	100	I	D	I×D
DM yield, kg/ha ×1000	18.9	18.2	19.2	21.5		18.9	20.5	20.1	21.6	0.13	0.44	0.23	0.80
Plant dry weight, g/plant	340	280	250	220		343	337	265	228	16	0.17	0.01	0.33
DM, %	27.7	27.4	27.7	26.7		27.8	27.7	27.6	25.5	0.53	0.10	0.36	0.46
CP, %	9.9	10.1	9.6	9.8		10.3	10.6	10.6	10.1	0.20	0.03	0.22	0.41
NDF, %	38.8	38.6	40.1	39.7		35.2	34.6	37.2	38.3	1.11	0.04	0.12	0.68
ADF, %	22.9	23.7	25.2	25.2		22.8	22.7	23.4	24.7	0.81	0.09	0.17	0.83
ADL, %	3.1	2.9	2.8	3.2		2.7	2.5	2.7	3.0	0.19	0.14	0.23	0.73
Starch, %	29.2	31.2	30.1	31.3		30.3	31.2	32.1	30.6	1.29	0.56	0.68	0.75
IVNDFD, %	55.1	55.5	56.0	53.9		55.1	55.9	56.3	54.3	0.78	0.60	0.08	0.99