Yield and Nutrient Utilization Efficiency of Irrigated Corn1

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Abstract
The concept of a critical concentration of each nutrient in plant tissue, below which poverty adjustment occurs and above which luxury consumption takes place, suggests a quantitative relationship between total uptake of each nutrient and yield in the range of poverty adjustment (RPA). The purpose of this investigation was to determine the relationships between yield of two hybrids of irrigated corn (Zea maysL.) at two populations (60 000 and 90 000 plants/ha) and each of the following variables: g/kg of N, P, and K in the tissue, and total uptake of N, P, and K 4 weeks after silking. Five levels of fertilization of (N‐P2O5,‐K2O) were applied to Pioneer brand hybrids ‘3369A’ in 1977 and ‘3368A’ in 1978 on a Ruston loamy fine sand (fine‐loamy, siliceous, thermic Typic Paleudult). The N‐P2O5K2O ratio was constant at 15‐10‐15 for all treatments. Nitrogen levels were 0, 1, 2, 3, and 5 kg/1000 plants with P and K at the above ratio. Irrigation was applied to recharge the plow layer when soil‐water suction reached 0.02 MPa at the 15‐cm depth. Maximum yields for 60000 plants/ha were 12.7 Mg/ha in 1977 and 10.4 Mg/ ha in 1978. At 90000 plants/ha, maximum yields were 14.5 Mg/ha in 1977 and 9.8 Mg/ha in 1978. Grain yields were significantly correlated with g/kg of N in tissue and total N uptake each year. Lower yields in 1978 were partly attributed to hybrid differences because ‘3368A’ had as high as 0.3 barren stalks at the 90 000 plants/ha population. Nutrient utilization efficiency (NUE) for each nutrient can be expressed without units as grain yield divided by total nutrient uptake. The NUE for N remained within a narrow range (61 to 67) in the RPA regardless of yield and population where the number of barren plants was not significant. Values of NUE for P and K reached maximum levels in the RPA.

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