Lysine and Protein Content of Normal and Opaque‐2 Maize Grain as Influenced by Irrigation and Nitrogen

Abstract

Increasing soil N fertility has been found to have detrimental effects on the nutritional quality of maize (Zea mays L.) grain; however, little research has evaluated the effects of irrigation on these factors. Most previous work has been done with inbred lines rather than high‐yielding commercial hybrids. This study was conducted to determine how irrigation and soil N levels would affect the content of protein and lysine plus the quality of maize protein as measured by the lysine in protein (LP). Two water regimes and five soil N levels were applied to two normal and two opaque‐2 commercial hybrids grown on a Sharpsburg silty clay loam soil (fine, montmorillinitic, mesic Typic Argiudoll). The hybrid ✕ year interaction indicated that in 1985 and 1987 the short‐season opaque‐2 hybrid (SO) had a greater yield than the short‐season normal hybrid (SN) by ≈8%, whereas the long‐season normal hybrid (LN) had a greater yield than the long‐season opaque‐2 hybrid (LO) by 4 to 12%. In 1986, normal and opaque‐2 hybrids produced similar yields. Irrigation increased yield, decreased protein content (PT) 5 to 7 g kg‐1, and increased LP by 1 to 2 g kg−1 in 1985 and 1986. Irrigation also decreased lysine in sample (LS) 0.3 g kg−1 for opaque‐2 grain. Conversely, increasing soil N levels increased yield, PT, and LS, while LP decreased quadratically from 0.39 to 0.36 % kg−1. Grain yield was maximized by production of LN hybrids with irrigation and high soil N levels. The highest PT levels were produced with normal hybrids with high soil N levels without irrigation. Grain produced by opaque‐2 hybrids under low soil N conditions without irrigation had the best protein quality as indicated by LP. Results from the study indicate that both grain yield and nutritional quality are influenced by hybrid selection, irrigation, and N fertilization, which should be considered by producers of nonruminant livestock.