Yield, Chemical Composition and Ruminal Fermentability of Corn Whole Plant, Ear, and Stover as Affected by Maturity

The nutritive value of corn (Zea mays L.) grain remains relatively constant; nutrient content and digestibility, however, may vary significantly in the remaining corn plant parts. Understanding of the relationships between plant maturity and plant component yield, nutrient content, and digestibility is important for prudent harvest management of nongrain corn parts. Six corn hybrids planted at two locations (Nampa, ID, and Modesto, CA) were used to evaluate the effects of maturity on yield, chemical composition, and ruminal fermentability of whole plant, ear, and stover. Maturities evaluated were: A, milk line ⅓ from the top of the kernel; B, milk line ⅔ from the top of the kernel; and C, black layer formation. Location × maturity interactions were not observed, therefore data were pooled across location. Neutral and acid detergent fiber (NDF and ADF) increased (P < 0.01) in stover and decreased (P < 0.05) in whole plant and ear samples when maturity advanced from A to B. Stover samples showed a further increase (P < 0.01) in these fiber components as maturity advanced from the B to the C stage. Whole plant and ear fiber composition did not change (P > 0.10) between the B and C maturities despite a progressive increase (P < 0.01) in grain composition of the whole plant. Calculations of total digestible nutrients (TDN) and net energy for lactation (NE1) based on the ADF content of the samples indicated differences (P < 0.01) between B and C maturities for stover samples but not for whole plant and ear samples. Stover samples, but not whole plant and ear samples, increased (P < 0.05) in lignin content with each increase in maturity. When ruminal fermentability was measured by incubating samples in situ for 24 h, percent dry matter (DM) disappearance was reduced (P < 0.01) with each advance in maturity for both the stover and the whole plant samples. The lower in situ DM disappearance for C vs. B maturity whole plant samples, which was not reflected in a similar reduction in calculated TDN, suggests an inadequacy in using ADF content as the sole indicator of the whole plant energy value. Yield of DM and of calculated TDN reached a plateau at the B maturity as no differences were observed for B vs. C maturity. These data indicate benefits to harvesting at proper maturity stages for corn whole plant, ear and especially stover.