Abstract
The objective of this study was to determine the effect of irrigation on neutral detergent fiber (NDF) and lignin (LIG) concentrations and on in-vitro apparent dry matter digestibility (IVDMD), and in vitro neutral detergent fiber digestibility (IVNDFD) of stems, leaf-sheaths, and leaf-blades of corn. Five commercial corn hybrids for silage (one of them showing the brown midrib phenotype) were planted in a split-plot setting within a randomized complete block design (4 replicates). Treatments consisted of a control treatment with furrow irrigation at planting and 3 more times during crop growth (IRRIGATED) and a non-irrigated treatment with furrow irrigation only at planting (NON-IRRIGATED). When the corn was between ¼ and ¾ milk-line stage of maturity, 5 plants from each plot were cut by hand, and stems, leaf-sheaths, and leaf-blades from the second phytomer below (LOWER) and the second phytomer above (UPPER) the ear insertion were dissected and frozen for analysis. Tissues were analyzed for NDF concentration, IVDMD, and IVNDFD. Data were analyzed using Proc Mixed of SAS, and the model included the effects of block (random, df = 3), treatment (fixed, df = 1), whole-plot error (random, df = 3), hybrid (fixed, df = 4), treatment by hybrid interaction (fixed, df = 4), and the residual or split-plot error (random, df = 25). IRRIGATED contained lower NDF concentrations (P < 0.01; 64.6 vs. 67.6% NDF) and greater IVDMD than NON-IRRIGATED plots (P < 0.05; 56.7 vs. 54.8% IVDMD). IVNDFD tended to be greater for IRRIGATED than for the NON-IRRIGATED plots (P < 0.10; 51.7 vs. 50.1% IVNDFD). Irrigation did not affect LIG concentration in the cell wall (P > 0.1)56, which averaged 19.9%. UPPER phytomers had a lower NDF concentration (P < 0.01; 64.4 vs. 67.7%) and a greater IVNDFD than LOWER phytomers (P < 0.01; 52.8 vs. 49.0%). In conclusion, under the conditions of this study, limited water supply does not affect lignin concentration in the cell wall and does not increase the in vitro digestibility of fiber in corn for silage. The latter observation is contrary to the general industry belief that water-stress increases fiber digestibility in forages.