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The Effects of Soil Temperature and Form and Level of Nitrogen on Growth and Chemical Composition of Italian Ryegrass

ABSTRACT

Italian ryegrass was grown in a clay loam soil in a greenhouse at 3 soil temperatures 11°, 19.5° and 28°C. with 6 levels of N (0 to 500 ppm.) as NH₄⁺ (treated with "N serve") or NO^3-. Tops grew best at 19.5° and roots at 11°C. At 19.5° yields of tops with NO₃-N were maximal at 100 ppm. and with NH₄-N at 200 ppm. Increasing NO₃-N above 100 ppm. greatly decreased yields of tops, but increasing NH₄-N did not. Yields of tops were larger with NO₃-N than with NH₄-N at low levels of N but were smaller at higher levels.

Root weights were similar with both forms of N, but whereas the roots were well distributed throughout the soil with NH₄-N, with NO₃-N, they were mainly confined to the top half of the soil.

Form of N greatly influenced the composition of the grass. Increasing NO₃-N decreased the concentrations of P, Cl and S, and NH₄-N decreased the concentrations of Ca. Percent N was larger with NO₃-N than with NH₄-N.

Raising the soil temperature greatly increased % Ca and % Mg but had little influence on concentrations of N, P, S, Na, and K. Percent Cl was always largest at 11°C.

¹ Experimental Farm, Swift Current, Saskatchewan, Canada. This work was done while on transfer at Rothamsted Exp. Sta., Harpenden, Herts., England.

² Rothamsted Experimental Station, Harpenden, Herts., England.

Received for publication July 23, 1963. Accepted for publication October 30, 1963.