Nitrogen fractions and soluble carbohydrates in italian ryegrass. I—Effects of soil temperature, form and level of nitrogen

In a glasshouse experiment Italian ryegrass S 22 grown for 9 weeks during October‐December in clay loam at three soil temperatures II°, 19.5° and 28° was given 6 levels of N (0—500 p.p.m.) as NH4+‐N or NO3−‐N. Tops grew best at 19.5° and with NO3−‐N yields were greatest at 100 p.p.m. and with NH4+‐N at 200 p.p.m. Increasing NO3+‐N above 200 p.p.m. greatly decreased growth but increasing NH4+‐N did not. At 100 p.p.m., NO3−‐N gave better yields than NH4+‐N but at 200 or more p.p.m. the reverse was true. Total‐N, total soluble‐N and nitrate‐N were much more, and protein‐N, amide‐N (particularly asparagine) and α‐amino‐N much less in grass given NO3−‐N than in grass supplied with NH4+‐N. These differences increased with increasing amounts of applied N. Increasing soil temperature considerably increased the total soluble‐N and decreased the protein‐N irrespective of the form of N added. With all treatments, plants contained very little carbohydrate; at 11 ° soluble carbohydrates decreased with increasing level of N, more with NH4+‐N than NO3−‐N. The causes of nitrate‐N accumulation in grass are discussed.