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Determining Optimum Nitrogen Rates for Irrigated Timothy Hay for Export

Very little work has been done on determining optimum nitrogen rates for Timothy hay.

IPNI-2015-USA-WA16

Overview Related Article
24 Apr 2015

Using Chlorophyll Measurements for In-Season Nitrogen Applications


This is a part of the Proceedings of the NW Hay Expo at Kennewick, WA January 14, 2015

Using Chlorophyll Measurements for In-Season Nitrogen Applications

By Steve Norberg, Don Llewellyn, Steven Fransen, Shannon Neibergs, (all WSU Extension).

    Nitrogen rates of timothy can be instantaneously assessed in the field using a Soil Plant Analysis Development (SPAD) units to determine optimum fertilization using fertigation. The SPAD meter measures how much of red light at 650 nm (best absorbed by the chlorophyll molecules) is absorbed by the sample and how much transmission of infrared light at 940 nm, at which no absorption occurs and gives a greenness measurement (SPAD unit). These SPAD units are compared to an over fertilized strip in the field and relative chlorophyll units (RCM) are calculated (field/over fertilized=RCM) for at least 20 measurements. Results for relative chlorophyll measurements are related to the amount of chlorophyll that is in the samples tested which is correlated with the nitrogen status of the field. The cost of a SPAD meter is about $2,500.

    Preliminary nitrogen recommendations at two growth stages 6” tall timothy (RCM Veg.) or 26” tall timothy in early boot (RCM Boot) were calculated for first cutting and are shown in Figure 1 below. First cutting vegetative stage chlorophyll meter and tissue samples were taken on May 6th in 2013 and April 29th in 2014 at Prosser as well as May 1st in Othello. First cutting boot stage chlorophyll meter and tissue samples were taken on May 13th in 2013 and May 5th in 2014 at Prosser and May 8th at Othello in 2014. First year leaf tissue critical values are also shown in Figure 3 for 2013. This work will aid producers’ decisions on how to optimize nitrogen rates during the season for each cutting as the season progresses with fertigation.

    Figure 1. Relative chlorophyll meter reading predicting adjusted gross revenue after nitrogen fertilizer cost averaged over both vegetative and boot stage growth stages at Prosser in 2013 and 2014 and Othello in 2014.



    Figure 2. Relationship between economic N rate in pounds per acre and relative SPAD meter value averaged over both growth stages (Vegetative stage (stem 6” height) & Boot stage). Relative SPAD meter value is the field value at time of measurement divided by heavy fertilized control.



      Figure 3. The relationship between economic N rate in pounds per acre and percent leaf tissue nitrogen at two growth stages in 2013 (Vegetative, Boot stage).
    · The data from the leaf tissue samples also looks promising to be able to assist in adjusting in-season nitrogen rates. The time the samples are taken must be considered as these samples were only one week apart at the stages given.
The Washington State Hay Growers Association support this work with grants in 2013 and 2014 as well as a grant from WSU BIOAg that supported this experiment.