Influence of relative time of emergence on nitrogen responses of corn and velvetleaf

Abstract

Nitrogen (N) management markedly affects weed competition with crops. The effect of N availability on plant competition varies with a plant's abilities to capture and use N. Accordingly, we expected the N effect on plant competition to change with the relative emergence time of competing individuals. This hypothesis was tested by growing corn and velvetleaf plants in target and neighbor roles and comparing their N responses. Sowing times were varied, so that target plant emergent dates were constant, whereas neighbor plants were sown to emerge 7 d before, with, or 7 d after targets. Seedlings were fertilized daily with 2.5 mmol (“low N”) or 10.0 mmol (“high N”) ammonium nitrate (NH4NO3). Corn had greater total weight, leaf area, and root-to-shoot ratio (RSR) than velvetleaf. Different dry weights may have reflected seed weights; corn seed weight was greater than velvetleaf. Regardless of role, corn and velvetleaf dry weight and leaf area were greater with high N than low N; in contrast, RSR was lower with high N than low N. The RSR response to N availability suggested plant resources were shifted from N foraging, toward competition for photosynthetically active radiation (PAR). In target plants of each species, dry weight and leaf area increased linearly with time between target and neighbor emergence. Conversely, dry weight and leaf area of neighbor plants decreased with time between target and neighbor emergence. The N response of neighbor plants increased with time of emergence between target and neighbor emergence. Larger plants likely required more N to sustain growth than smaller plants; plants that emerged earlier likely had greater daily N requirements than those that emerged later. These results support factoring in emergence when predicting N effects on plant competition. Optimal N provisioning for integrated weed management may differ with emergence times of competing plants.

Strip Intercropping of Rye–Vetch Mixtures: Effects on Weed Growth and Competition in Strip-tilled Sweet Corn

“…One explanation for greater response of sweet corn to Vetch IR :RyeVetch IR ratio and soil inorganic N %IR compared with weeds is that sweet corn more rapidly acquired early mineralized N released from vetch. Corn is a relatively large-seeded crop with a high relative growth rate that allows corn plants to rapidly establish their root systems and scavenge soil resources (Harbur and Owen 2006). In comparison, most weed species are small-seeded (Seibert and Pearce 1993), and despite having a high relative growth rate, their small seed size puts them at a considerable initial disadvantage because of lower energy reserves to devote toward root proliferation.…”

Weed management and nitrogen loss in glyphosate-resistant corn (Zea mays)

“…Delayed POST application can lead to weed competition early in the growth cycle of corn. Alternatively, the lack of residual activity of glyphosate leads to the presence of weeds later in the season Harbur and Owen 2006;. Many studies have shown that the emergence and density of weeds are critical factors in determining the level of competition.…”