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Irrigated Annual Ryegrass Responses to Nitrogen and Phosphorus on Calcareous Soil
Author(s) -
Lippke Hagen,
Haby Vincent A.,
Provin Tony L.
Publication year - 2006
Publication title -
agronomy journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.752
H-Index - 131
eISSN - 1435-0645
pISSN - 0002-1962
DOI - 10.2134/agronj2005.0236
Subject(s) - lolium multiflorum , agronomy , forage , calcareous , dry matter , phosphorus , fertilizer , irrigation , nitrogen , calcareous soils , grazing , biology , chemistry , botany , organic chemistry
Annual ryegrass ( Lolium multiflorum Lam.) is increasingly being planted under irrigation as forage for stocker cattle in south central USA, but fertilizer recommendations for maximum production are not well defined. Labile N and P are generally deficient in this region's calcareous soils; K availability is usually considered adequate for plant growth. Growth responses of annual ryegrass to a factorial array of five levels of N and four levels of P were studied for 3 yr on a Knippa clay soil (fine, mixed, superactive, thermic Vertic Calciustolls). Responses to N and P were generally curvilinear, but they also had a strong linear component in Year 1. Increments of growth responses to levels of fertilizer above 269 kg applied N or 39 kg applied P ha −1 were relatively small. Response surface models projected maximum annual dry matter yields that averaged 9.23 t ha −1 and were associated with predicted requirements for applied N and P that averaged 488 and 61 kg ha −1 , respectively. Economically optimal levels of applied N were predicted to range from 250 to 315 kg ha −1 ; the predicted economically optimal range for applied P was 31 to 41 kg ha −1 . Nitrogen concentration in ryegrass forage increased as applied N increased. The data suggest that fertilizing vegetative ryegrass to maintain N in leaf tissue ≥32 g kg −1 provides economically optimal growth for both the ryegrass crop and the young cattle grazing it.