Nitrogen Management in Irrigated Corn

Russell Ranch Biomass YieldCorn production for silage and grain in California has occupied between 420,000 and 670,000 acres of arable land annually over the last ten years (USDA-NASS).  Despite that corn is an important cropping system in California, current models and crop coefficients for nitrogen (N) uptake and evapotranspiration (ET) for corn have been developed in regions that have different soil types, overall climate, and that utilize different irrigation techniques from California.  This project seeks to develop an N uptake curve relative to cumulative ET for maize in California, relate that curve to canopy and leaf reflectance values measured in real-time by proximal sensing devices, and determine if those proximal sensing values can be used to indicate crop N and water deficiency in real-time.

Two experiments have been ongoing during the summer of 2018 in the Sacramento Valley: one at the Russell Ranch Research Facility of UC Davis and one at a grower’s field in the Delta region.  The Russell Ranch experiment consisted of five treatments combining three irrigation rates (25%, 50%, and 100% ET) and three nitrogen fertilizer rates (25 lb/acre, 105 lb/acre, 210 lb/acre UAN-32) across four replications.  The Delta experiment consisted of two treatments across four replications, one with 125 lb/acre Anhydrous Ammonia and one without applied nitrogen.  To calculate nitrogen uptake, seven in-season biomass harvests were conducted at each site.  Biomass yield and tissue N concentration will be used to determine total N uptake across treatments.  ET will be estimated using local weather data, soil moisture, Leaf Area Index (LAI), and canopy temperature measured using infrared radiometers.  Drone generated multispectral aerial images were taken weekly and will be used to calculate indices such as NDVI, GRVI, and OSAVI.  NDVI was also measured using a handheld Greenseeker device and total chlorophyll was measured using an AtLeaf.

These indices will be assessed for their ability to predict yield and N uptake patterns across the treatments.  The goal is to translate the information gained from this experimental effort into decision support information that will help growers to make informed, real-time decisions about how their crop is likely to respond to added nitrogen. Data relating cumulative ET and N uptake will enable growers to utilize practices that combine water and nitrogen applications and plan their N applications for periods of rapid N uptake by the crop.  This will ensure maximum efficiency of nitrogen and water by the crop and help minimize losses to the environment.

Russell Ranch GRVI and RGB images