Managing Nitrogen for Crabgrass Hay Production

Abstract

Much of the forage produced in the subhumid areas of the USA is from cool‐season species, which mature and become dormant in early summer. This results in minimal forage produced in mid‐ to late summer, a time referred to as a “summer slump.” ‘Red River’ crabgrass [Digitaria ciliaris (Retz) Koel.] is a productive warm‐season annual that can fill this void, but optimum N fertilizer management for this species is unknown in much of the eastern plains of the USA. We tested N rates of 0, 50, 100, 150, and 200 lb N/acre from two sources, urea and ammonium nitrate, applied as single or split applications, on two cuttings during two years that contrasted in rainfall. A yield plateau was reached just above 100 lb N/acre both years, although yield was 2× higher in the moist year. However, forage fertilized with more than 100 lb N/acre generally had a higher N concentration than forage that received less N. Split application often resulted in less forage with a lower N concentration in the first cutting, but more in the second cutting than a single N application. Responses to N source were small, with application as ammonium nitrate yielding more than urea only in the second cutting at lower N rates.

Nitrogen Fertilization Affects Economic Return from Crabgrass Hay

“…The plot area at the Mound Valley Unit of the Kansas State University Southeast Agriculture Research Center had < 12 inches of topsoil (Parsons silt loam, fine, mixed thermic Mollic Albaqualf) over a thick claypan subsoil. It was treated as reported earlier (5), including fertilization with 60 lb/acre each of P 2 O 5 and K 2 O each spring, seeding initially with 5.0 lb/acre of pure, live Red River crabgrass seed using a Brillion seeder, and broadcasting another 3.0 lb/acre of pure, live seed each succeeding spring, followed by light tillage of 2 to 3 inches with either a disk harrow or rotary‐hoe.…”

“…Forage was harvested and weighed from a 3‐ by 20‐ft strip at 2.5‐inch height as described by Moyer and Sweeney (5). Subsamples were collected and oven‐dried at 130°F for dry matter determination, then ground with a Wiley mill to pass a 1‐mm screen and analyzed for N concentration as described in (5).…”

“…Annual average CP each year was determined by dividing total annual forage N by total dry matter production, and multiplying the result by 6.25. The SAS mixed‐model program using treatment and year as fixed effects (SAS Institute Inc., Cary, NC) indicated that N rate was the major treatment effect for measured variables (5). The SAS OLS and NLIN procedures (SAS Institute Inc.) were used to analyze yield and CP response to N by examining several different functional forms (linear, linear plateau, quadratic, quadratic plateau, and Mitscherlich models) for determining the relationships of N vs. yield and CP.…”

“…1. Yield response to N rate was best characterized as a linear plateau, as it was for total annual yield in the individual years of 2006 and 2008 (5). The plateau for the 3‐year average yield occurred at 107 lb N/acre, while the average CP response to N rate was a linear relationship.…”

“…Previous reports have shown the crabgrass yield response to the use of N fertilization in Oklahoma (2), Virginia (7), and more recently in the subhumid plains of southeastern Kansas (5). The Virginia trials indicated that the economic optimum N application rate varied between 100 and 225 lb/acre under general production practices and pricing conditions (7).…”