Long-Term Rye-Wheat-Ryegrass Forage Yields as Affected by Rate and Date of Applied Nitrogen
- Wadell Altom,
- Jerry L. Rogers,
- William R. Ram**,
- Gordon V. Johnson and
- Shannon L. Taylor
Forage yield and quality can be affected by time and rate of N application. This study was conducted to evaluate the long-term impacts of time and rate of applied N on rye (Secule cerede L.,)-wheat (Triticum aestivum L.)-ryegrass (Lolium multiyorum Lam.) forage yield and protein considering seasonal (fall-winter and spring) production differences. Rye-wheat-ryegrass mixtures have been commonly used to extend the forage production season. A long-term experiment was initiated in 1979 to evaluate the effects of N timing (all N applied preplant in the fall, all N applied in the spring, or split applied in the fall and spring), N rate (0, 50, 75, 100, 150, and 200 1b N/acre) and applied lime (no lime or single application of 2 tons/acre). Harvests were classified into two groups, fall-winter (November through February) and spring (March through June) with 5 March being the separation date between the two groups. An average of five harvests were obtained each year (two in the fall-winter and three in the spring). No differences in fall-winter, spring, or total forage production and forage protein were observed as a result of applied lime. In general a linear response to applied N up to 200 lb of N/acre was observed in fall-winter, spring, and total forage yields. Fall-winter forage production was higher when N was applied in the fall. Similarly, spring forage production was higher when N was applied in the spring. No differences in total forage production were observed over this 14-yr period between fall, spring, and split applied N. Forage protein was much higher in fall-winter harvests (before 5 March) than spring harvests. Total forage N removed (fall-winter plus spring production) tended to be somewhat higher when all fertilizer N was applied in the fall compared with split and spring N applications. Estimated N use efficiencies did not decrease with increasing N applied as has been reported in grain production systems. Forage production systems may have lower plant gaseous N loss (improved N use emciency) because the plant is never allowed to approach flowering when N losses have been found to be greater.
Cool-season grasses provide excellent forage potential from early fall to late spring in much of the Southern Great Plains. High forage yields can be sustained when adequate N fertilizer is supplied. This research evaluated the effect of N rate and timing on seasonal and annual rye-wheat-ryegrass forage yield and protein over 14 yr.
Previous work has shown that grass species vary in their responsiveness to rates of applied N and time of application (preplant or midseason). Similar response has been found to urea and ammonium nitrate fertilizers. When N rates exceed requirements for maximum forage production, N use efficiency decreases and residual mineral N accumulates in the soil.
Ryegrass was broadcast over a mixture of rye and winter wheat drilled in 6-in. rows in late September or early October. Ammonium nitrate, at N rates up to 200 lb/acre, was fall applied (broadcast shortly after planting), spring applied (broadcast between mid February and mid March), or split applied (for N rates of 100 lb/acre or greater, half fall and half spring). Fall and winter forage was harvested prior to March and spring growth was harvested from March through June. Fourteen years of data have been collected since initiation in 1979.
How much does N fertilizer increase yields?
Total yields without fertilizer averaged about 2000 lb/acre and were increased to about 5000 lb/acre at the 200 lb/acre N rate. The increase was linear, indicating an increase of about 15 Ib forage per pound of N applied and that higher yields probably could be obtained from rates greater than 200 1b N/acre.
Should N be applied in the fall or spring?
Forage yields were always greatest in the season in which fertilizer N was applied. However, spring yield response to spring applied N was greater than fall response to fall applied N. Consequently, although spring applied N was not all used in the spring, the carryover to the next fall resulted in a lower, yet linear, yield and protein response. Annual (fall plus spring) forage production was similar for fall, spring, and split-applied N. Fall-applied N resulted in the most uniform forage production (about 2300 1b of forage in both the fall and spring) and spring-applied N resulted in the most uniform protein content (about 20 % in the spring and 23 % the following fall) at the high N rate.
Are there advantages to split applied N fertilizer?
Split applications resulted in the most uniform production of plant protein, about 550 lb/acre of plant protein during both the fall and spring production periods. Spring applied N produced about 700 lb of forage protein in the spring and only about 300 in the fall, while fall applied N produced nearly 700 lb of forage protein in the fall but only about 450 Ib in the spring.
How does fertilizer timing affect N use efficiency?
Nitrogen use efficiency was higher for fall applied N and split applied N. Lower N use efficiencies for spring applied N are apparently a result of more N present in forms that can be lost (nitrate and ammonium) by denitrification, leaching, and volatilization during the season when soils are more commonly wet and predisposed to these processes. Nitrogen use efficiencies were above 60 % and considerably higher than commonly found in grain production systems. However, N use efficiencies may well have decreased if maximum yields had been achieved.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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