Systems evaluation of shallow anhydrous ammonia placements, rates, and timing on maize plant uniformity, yield, and N use efficiency

Peter Kovacs, Purdue University

Abstract

Farmers face increasing expectations from society to be more environmentally conscious and energy efficient with their fertilizer management practices during maize (Zea mays L.) production. Field studies were conducted between 2010 and 2012 near West Lafayette, IN to identify best management practices to enhance maize plant uniformity, yield and nitrogen (N) efficiencies. The first field studies were conducted to compare maize plant growth, grain yield, and plant-to-plant variability responses to two shallow pre-plant NH3 placements (diagonal to the row versus parallel but 15-cm offset from the row) to a depth of about 12 cm in both no-till and conventional tillage systems at N rates of 145 and 202 kg N ha-1. Contrary to expectations, parallel NH3 application did not generally improve plant-to-plant uniformity in either plant growth (plant height, stalk diameter, stem volume), plant N status (leaf SPAD readings) or in final grain weight, relative to diagonal application, across a range of tillage and N rate treatments. Perhaps the parallel application treatment placed the NH3 too close (15 cm) to the maize rows, especially in the year with the shortest time interval between NH3 application timing and planting (only one day in 2011). In 2011, increased plant-to-plant variability was already present at seedling emergence and persisted through the growing season, and more barren plants and increased variation in kernel number and per-plant grain weight were observed than in 2010 and 2012. Conventional tillage generally lowered plant-to-plant variation for most plant parameters measured, and resulted in consistently higher yields than no-till. Plant responses were only minimally influenced by varying distance within the row from the point of row intersection with the NH3 band in diagonal-applied treatments. Another three-year field study investigated the effect of timing (and associated placement) of shallow NH3 on maize grain yield (GY A), N recovery efficiency (NRE), and N use efficiency (NUE) at multiple N rates. Three NH3 application timings (100% pre-plant in spring just days before planting, 100% side-dress at V6-V7 growth stage, and split NH3 applications) and four N rates (0, 90, 145, and 202 kg N ha -1) were evaluated in a factorial combination. The NH3 was injected to a depth of 12 cm. Pre-plant NH3 was banded parallel to, but about 15 cm offset from, the intended maize rows, while the side-dress NH3 was applied in the traditional mid-row position for maize grown in 76.2 cm row widths. Maize GYA, and whole-plant N accumulation at maturity almost doubled with increasing N rates in 2010-2011, but maize response to NH3 in 2012 was limited by severe drought stress. Highest GYA was observed with the side-dress 202 kg N ha-1 rate in 2010-2011, but with the pre-plant 202 kg N ha-1 rate in 2012. However, whole-plant N uptake was consistently highest in the pre-plant 202 kg N ha-1 treatment in both 2010-2011 and 2012. Pre-plant NH3 application improved NRE from 0.60 to 0.67 kg plant N kg -1 applied N in 2010-2011 but from 0.39 to 0.67 kg plant N kg -1 applied N in 2012, relative to side-dress NH3 (whole-plant N recovery equaled ~ 67% of applied N fertilizer across pre-plant N rates in 2010-2011 and 2012). Average NRE and NUE (based on GYA gain to the added fertilizer compared to 0 kg N ha-1 treatment) declined with increasing N rates as expected. Although overall NUE levels in 2012 declined by more than 55% relative to 2010-2011 due to drought, pre-plant and split NH3 applications achieved much higher NUE than side-dress. This study highlighted the GYA and NUE vulnerability of one-time NH3 application strategies in maize production with inclement weather, and the occurrence of sometimes wide divergences between NRE and NUE in treatment responses to both NH3 rates and timing. (Abstract shortened by UMI.)

Degree

Ph.D.

Advisors

Van Scoyoc, Purdue University.

Subject Area

Agronomy

COinS