"Nitrogen Fertilizer Placement and Rate Impacts Sunflower Seed Yield, O" by Rojina Kafle

Document Type

Thesis - Open Access

Award Date

2024

Degree Name

Master of Science (MS)

Department / School

Agronomy, Horticulture, and Plant Science

First Advisor

Thandiwe Nleya

Abstract

South Dakota accounts for about 36% of the total US commercial sunflower production and nitrogen is a major input. Costs related to N fertilizer demand economically optimum N rates. This study investigated the impact of the N fertilizer placement method (broadcast vs band) and rate (0, 28, 56, 84, 112, 140 kg N ha-1) on leaf chlorophyll content, head diameter, seed yield, seed oil, and protein concentration of three sunflower hybrids in 2022 and 2023. The experiment was conducted at Brookings (eastern SD- conventional till, 66 cm rainfall) using an oil-type hybrid and at central SD sites (no-till, 57 cm rainfall) using a confectionary hybrid at Miller (2022) and an oil-type hybrid at Highmore (2023). The fertilizer treatments were applied three weeks after planting using urea (46-0-0) for the broadcast treatment and liquid UAN (28-0-0) applied with a Y-drop for the band treatment. In-season drone imagery was used to evaluate treatment impacts on canopy development and vegetative greenness. Leaf chlorophyll content, plant height, stem diameter, and NDVI increased with increasing N rate (P<0.001). Seed yield increased with increasing N rate and peaked at 84 kg N ha-1 at Brookings in 2023 and Miller in 2022. In oil-type sunflower, oil concentration decreased with increasing N rate whereas protein concentration increased linearly. The economic optimum nitrogen rates (EONR) for sunflower grown under conventional till system was 71 kg ha-1 for band and 72 kg ha-1 for broadcast. In the no-till system, EONR for band was 74 kg ha-1and that for broadcast was 71 kg ha-1. Findings from this study suggest V-11, R-1 and R-5 are important sunflower growth stages for extracting in-season remote sensing imagery for vegetative greenness related to crop performance. In both conventional and no-till systems, 84 kg N ha-1 was sufficient to obtain the greatest yield indicating that current N recommendations may be reduced by 20-40 kg N ha-1 without yield loss. Afterall applying N levels above 84 kg N ha-1 contributed to excess vegetative growth at the expense of seed yield and oil content reducing the profitability of the crop.

Publisher

South Dakota State University

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Rights Statement

In Copyright