Management of Corn for Silage Production in South Central USA

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Abstract
Relocation of large dairy operations into the south central USA during the mid-1980s created the need for local production of large quantities of high-quality forage. Corn (Zea mays L.) silage was recognized as a forage for meeting this need, but production information was limited. Corn was grown at Stephenville, TX, on Windthorst fine sandy loam (fine, mixed, thermic Udic Paleustalf) soil during 1987, 1988, and 1989 to determine optimum fertilizer N rate and plant density, and to compare dryland production with supplemental irrigation. Dry matter yield, partitioning of dry matter to morphological components (ear, stalk, and leaf), forage quality, stalk diameter, and production economics were studied. Water treatment was either dryland or dryland plus supplemental irrigation. Nitrogen rates were 0, 160, and 320 lb/acre annually. Plant densities were 7 300, 14 500, 29 000, and 58 000 plants/acre. Supplemental irrigation increased dry matter yield in 1987 and 1988, increased digestible dry matter yield all years, reduced leaf percentage in 1987 and 1988, decreased stalk percentage in 1987, and increased ear percentage in 1987. Dry matter yield increased as plant density increased at the 160 and 320 N rates each year and at 0 N in 1989. Digestible dry matter yield increased with increasing plant density. Ear percentage decreased at 160 and 320 lb N/acre as stalk and leaf percentage increased. Stalk diameter increased at 160 lb N/acre each year. Increasing plant density for all N rates and water regimes reduced stalk diameter. Economically, the highest return occurred at 160 lb N/acre and a plant density of 29 000 (dryland corn; $138.56/acre) to 58 000 (irrigated corn; $154.06/acre) plants/acre. The difference in net return between dryland and irrigated corn at optimum N rate and plant density was $15.50/acre (not accounting for labor and fixed costs). We conclude that dryland corn fertilized with 160 lb N/acre and grown at a plant density of 29 000 plants/acre produced the optimum dry matter yield and profit. Less costly water could improve profitability of supplemental irrigation. Research Question Relocation of large dairy operations to concentrated drylot systems in the south central USA and growth of the existing dairy industry in that region have created a need for large quantities of high-quality forage. While locally produced corn silage would meet such a need, limited management information was available for corn silage production in this region, which is characterized by erratic rainfall, low soil N, and high air temperatures during pollination and grain filling. Our objective was to provide information for profitable production of high-quality corn forage. We studied the effects of supplemental irrigation, N rate, and plant density on forage yield; economic returns; the nutritive characteristics of whole plants, ear, leaves, and stalks; and the proportion of total dry matter in each morphological component. Digestibility and lignocellulose composition of corn forage are reported in a companion paper. Literature Summary Corn grain yields are decreased up to 50% by water stress before and after silking and up to 46% for 4-wk stress periods during vegetative growth stages. Densities of 35 000 plants/acre have increased dry matter yield but the effect on ear percentage of total dry matter has been variable. Nitrogen requirements for grain yield have ranged from 114 to 338 lb/acre at several locations. Plant densities 10 to 25% higher than for grain corn are recommended in other regions for silage corn production. Little information is available for production of silage corn in the south central USA. Study Description Location: Stephenville, Texas Soil: Windthorst fine sandy loam Treatments: Water regimes: Dryland, supplemental irrigation N rates: 0, 160, 320 lb/acre Plant densities: 7 300, 14 500, 29 000, 58 000 plants/acre Corn hybrid: Pioneer ‘3165’ Herbicide: Metolachlor (1 qt/acre) Insecticide: Chlorpyrifos (1989, 1.1 lb ai/acre) for control of soil-borne insects Harvest stage: Late dough (approximately 65% moisture) Rainfall (growing season): 1987—15.1, 1988—12.5, 1989—19.2 in. Irrigation: 1987—4.7, 1988—8.9, 1989—5.5 in. Applied Question How did supplemental irrigation affect yield, digestible dry matter, and proportion of ear, stalk, and leaf? Irrigation increased dry matter yield 1.4 tons/acre in 1988, when rainfall amount and distribution during the growing season was near average (Table 1). Yield increased only 0.3 tons/acre in 1987, when 83% of the growing-season rainfall occurred in May and June and did not increase in 1989 when rainfall was above average. Irrigation increased the yield of digestible dry matter an average of 0.57 tons/acre each year due to higher yield, not increased digestibility. Irrigation increased ear proportion by 11 percentage units in 1987, whereas the stalk and leaf components decreased by 5 and 6 percentage units. How did N rate and plant density affect dry matter yield, digestible dry matter, stalk diameter, and ear, stalk, and leaf proportion? Both yield and digestible dry matter yield increased each year as plant density increased for N-fertilized corn, but not for nonfertilized corn. Typical response to increasing plant density at 160 lb N/acre occurred in 1988, a year of near-average rainfall (Fig. 1a). Averaged for all plant densities, N fertilizer increased yield 233% in 1987, 56% in 1988, and 88% in 1989 compared with no N, and there was no difference between the 160 and 320 N rates. Generally, ear percentage decreased and stalk and leaf percentage increased as plant density increased, particularly in nonfertilized corn (Fig. 1b). Irrigation changed ear, stalk, and leaf proportion slightly in 1987 (Table 1). Stalk diameter increased as N increased from zero to 160 lb/acre, but decreased each year as plant density increased. Figure 1 Open in figure viewer PowerPoint Effect of plant density and N (160 lb/acre) on dry matter yield and digestible dry matter yield in 1988(a); and on percentage ear, leaf, and stalk of total dry matter in 1987(b). What agronomic inputs resulted in the highest net returns above specified costs? A N rate of 160 lb/acre and a plant density of 29 000 plants/acre resulted in $142/acre net return above specified costs during 3 yr with supplemental irrigation (Table 2). Doubling the plant density to 58 000, which is much higher than is generally recommended, further increased net returns by $12/acre. Net return from dryland corn was highest ($139/acre) at 29 000 plants/acre and 160 lb N/acre and decreased at higher plant density. The maximum difference in net return between irrigated and dryland was $15/acre, which must cover the cost of labor and fixed expenses. Table 1. Effect of moisture regime on dry matter yield and digestible dry matter in 1988, and morphological components of corn in 1987. Moisture regime DM yield Digestible DM Ear Stalk Leaf ----tons/acre(1988)---- % of whole plant dry matter(1987) Irrigated 5.6 4.5 46.9 25.8 16.4 Dryland 4.2 3.4 35.8 31.2 22.6 Table 2. Three-year mean for the effect of plant density and N rate on net returns of dryland and irrigated corn silage. Plant density per acre No N 160 lb N/acre -------- Net return†, $/acre --------- Dryland 7 300 79.41 109.49 14 500 102.11 127.41 29 000 97.22 138.56 58 000 70.54 133.30 Irrigated 7 300 45.46 90.30 14 500 40.61 136.16 29 000 32.09 142.42 58 000 20.50 154.06 † Above specified costs. Assumes N = $0.25/lb, seed = $0.90/1000. custom harvest = $6.50/ton, irrigation pumping cost = $7/acre-in., and silage value = $21/ton. Yield adjusted to 35% dry matter. Recommendations For corn silage production in this area, an N rate of 160 lb/acre and a plant density of up to 29 000 plants/acre would be best under dryland conditions.