Root mass as a determinant of com hybrid response to starter fertilizer

Abstract

Many studies have shown variable response to starter or row applied fertilizer on corn (Zea mays L.) hybrids. Field experiments with approximately 25 hybrids over three seasons showed that some hybrids responded to row applied fertilizer with large growth and yield increases while others did not respond. The objectives of this study were to compare root and shoot growth of responsive and non‐responsive corn hybrids to starter fertilizer and their uptake of nitrogen (N) and phosphorus (P). Two glasshouse experiments were conducted with hybrids from the field studies found to be most and least responsive to row applied fertilizers. In the first experiment, P was applied at levels of 0,10,20, or 30 mg kg^‐1 and was mixed with either 25 or 100% of the total soil volume (1.5 L). Nitrogen was mixed with the total soil volume in all treatments at a rate of 100 mg pot^‐1. Phosphorus rates in the second experiment were 0, 30, or 60 mg kg^‐1 and the N rate was 200 mg pot^‐1. Fertilizer N and P were mixed with total soil volume or banded 5 cm below the soil surface and 5 cm away from seed. The soil was obtained from the A horizon of Norfolk loamy fine sand (fine loamy, siliceous, thermic, Typic Kandiudult). Time from seeding to harvest was 33 days for the first experiment and 41 days for the second. Root weight of the non‐responsive hybrid was 31 % higher in the first experiment and 48% higher in the second than of the responsive hybrid. Each hybrid responded similarly to starter P (62 to 78% increase in top growth). The responsive hybrid produced a significant (P 0.05) increase in top (92%) and root (76%) weight due to starter N, but the non‐responsive hybrid did not respond to N placement. The lack of response to starter N‐fertilizer was attributed to greater root growth in the non‐responsive hybrid because its top and root weight with broadcast N were about the same as those of the responsive hybrid with banded (starter) N. Since the hybrids differed only in response to starter N, a convenient method to classify corn hybrids with respect to starter fertilizer response is to measure top growth at six weeks after planting with banded versus broadcast N applied at planting.