Abstract

Hot weather, limited rainfall during the growing season, and low soil fertility limit corn (Zea mays L.) production for silage in south central USA (e.g., Texas). Our objective was to examine the effects of supplemental irrigation, plant density, and N rate on quality of forage maize. Pioneer brand hybrid 3165 was planted at four densities (7 250, 14 500, 29 000, and 58 000 plans/acre) in rows spaced 3-ft apart in 1987, 1988, and 1989. Nitrogen was applied at 0, 160, or 320 lb/acre each year. Plots were either not irrigated or received supplemental irrigation when plants exhibited leaf rolling. Treatments were arranged as split-split plots randomized in four complete blocks. Water treatments were whole plots, N rates subplots, and plant densities were sub-subplots. Plots were harvested at dent stage of grain (33 to 37% dry matter). Whole plants, leaf blades, and stalks were analyzed for in vitro true digestibility (IVTD), acid detergent fiber (ADF), cellulose, and acid detergent lignin (ADL; except leaf blades) via near infrared reflectance spectroscopy (NIRS). In 1987, concentrations of ADF, ADL, and cellulose increased by 20 to 40%, whereas IVTD was reduced by 4 to 6% in all components with increased plant density when 160 or 320 lb N/acre was applied, whereas under 0 N fiber concentrations and IVTD changed little, if any, with increased plant density. Supplemental irrigation did not affect whole-plant forage quality, whereas IVTD of leaf blades and stalks from irrigated plots was reduced by 3 to 5%, respectively, with applied N in 1988 but not in 1987 or 1989. Quality of corn forage may have to be considered in plant density recommendations.

Research Question

Erratic rainfall during the growing season, high temperatures during flowering and grain set, and low soil fertility often limit production of forage corn in the south central USA. We examined the effect of supplemental irrigation, N fertility, and plant density on the forage quality of corn morphological components during 3 yr.

Literature Summary

Recommended production practices for forage corn are similar to those for grain corn. Plant density, however, often is increased for forage corn to increase biomass yield. Plant density, N fertility, and irrigation all affect the partitioning of dry matter (DM) to leaf, stalk, and ear. Most management recommendations are based on the assumption that practices that maintain or increase ear proportion in grain corn also will increase forage corn quality by increasing the proportion of grain. Some researchers have questioned the importance of maintaining a high proportion of ear in forage corn.

Study Description

Three N rates and four plant populations were evaluated under irrigated or dryland conditions from 1987 to 1989 at the Texas A&M University Research and Extension Center at Stephenville.

Soil: Windthorst fine sandy loam Experimental design: Randomized complete block with a split-split plot arrangement of treatments. Four replicates.

Irrigation: Overhead sprinkler N treatments: 0, 160, and 320 lb/acre Plant populations: 7 250, 14 500, 29 000, and 58 000 plant/acre in 36-in. rows.

Plots were harvested at dent stage and separated into whole plants, leaf blades, ears, and stalks. All plant samples were analyzed for in vitro true digestibility, acid detergent fiber, cellulose, acid detergent lignin (whole plants and stalks only), and crude protein (whole plants only) via near infrared reflectance spectroscopy. Concentrations of acid detergent fiber and crude protein were used in a decision support computer program (FORAGVAL) to estimate animal average daily gain and forage intake.

Applied Question

What effects do N rate, plant population, and irrigation have on estimates of forage quality?

Digestibility decreased, whereas acid detergent fiber, cellulose, and acid detergent lignin concentrations of whole plant corn increased with increased plant density when N was applied at 160 or 320 lb/acre (Table 1). Similar changes were noted in leaf blades and stalks. The changes in quality of whole plant corn were related also to the proportion of ear in the whole plant. Supplemental irrigation affected leaf blade and stalk in vitro true digestibility and lignocellulose concentration depending on the amount of N applied, but did not affect whole plant quality. Digestibility and fiber components were affected less by N fertilization than by plant density. Estimated forage intake and average daily gain increased with increasing N rate, whereas the amount of cottonseed meal needed to supply adequate protein decreased. Estimated average daily gain and forage intake decreased with increasing plant density. These data suggest that digestibility and fiber concentrations should not be a factor in N fertilizer recommendations; however, quality of corn forage may have to be considered in plant density recommendations.

Copyright © 1995. . Copyright © 1995 by the American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America, 5585 Guilford Rd., Madison, WI 53711 USA