Italian rye-grass given ammonium sulphate or sodium nitrate at 56 or 112 lb. N/acre was analysed for total nitrogen, soluble nitrogen (non-protein-nitrogen) and soluble carbohydrates.Ten days after applying fertilizer the differences in total-N between the grass receiving 56 and grass receiving 112 lb. N/acre were very small. Total-N in grass decreased with growth, but the effect of the rate of nitrogen on total-N increased. At first the grass given sodium nitrate contained more soluble nitrogen than grass given ammonium sulphate, the difference being greater at 56 lb. N/acre; soluble nitrogen decreased with increasing growth. Ten days after applying fertilizer, the nitrate-N content of grass was very high (ranging from 0·1 to 0·9% in the D.M.) and it gradually decreased. At both levels of nitrogen application, grass given sodium nitrate contained much more nitrate-N than grass given ammonium sulphate. Forty days after applying nitrogen the nitrate-N contents of grass which received 56 and 112 1b. N/acre as ammonium sulphate were 0·039 and 0·222% of the dry matter, respectively; the grass supplied with sodium nitrate gave values of 0·082 and 0·438%.Total soluble carbohydrates in the grass were small early in growth and gradually increased. Nitrogen dressings had little effect on the content of soluble sugars (glucose + fructose + sucrose) but greatly decreased the fructosan. The pattern of changes in the total soluble carbohydrate content followed that in fructosan content. Early in growth, the total soluble carbohydrate/crude protein ratio was very small in grass from all treatments except the ‘control’. This ratio increased with growth and at the last sampling was 2·13 in grass receiving no nitrogen, and in grass supplied with 56 and 112 lb. N/acre as ammonium sulphate it was 1·44 and 0·72 respectively; the corresponding figures for grass receiving sodium nitrate were 1·13 and 0·66. The total soluble carbohydrate carbon/soluble nitrogen ratio in grass with no nitrogen was 18 at the first sampling and it increased gradually, reaching 70 at the last sampling. This ratio was considerably less with all nitrogen treatments than with ‘control’. The values obtained with 112 lb. N/acre were less than those obtained with 561b./acre, irrespective of the form of nitrogen used.The relationship between the soluble carbohydrate carbon content and the soluble nitrogen in grass is illustrated graphically and discussed.
In a controlled-environment pot experiment sulphur fertilisers increased the yields of ryegrass when large dressings of nitrogen were also given. Yield responses to sulphur occurred when the dry matter contained less than 0.20% S . At the third cut, sulphur deficiency decreased concentrations of reducing sugars but had little effect on sucrose and fructosan in the grass dry matter. Only 44% of the nitrogen in the most sulphur-deficient grass was protein-N as compared to over 80% in non-deficient grass. The non-protein-N accumulated predominantly as amides especially asparagine. The amino acid composition of the insoluble protein, including the proportions of cystine and methionine, was unaffected by acute sulphur or nitrogen deficiencies.
Two pot experiments, one with 23 factorial (1969) the other with 33 factorial (1970) N x K x Na design, showed that yields of Italian ryegrass (Lolizrm multiJlorum) were increased by both potassium and sodium, when sufficient nitrogen was given but responses to potassium were larger than to sodium. Yields were only increased by potassium fertiliser when the grass contained less than 2.0 % K in the dry matter, irrespective of the Na content.The main effect of potassium and sodium on the soluble carbohydrates was to increase the production of fructosan; again potassium was more effective than sodium.Total N concentrations in the grass decreased with the increased production of dry matter from potassium and sodium fertilisers. Ammonium N, nitrate N and soluble organic N (expressed as the percentage of total N) were also decreased by potassium and sodium. In 1969, both potassium and sodium increased the percentages of most amino acids and decreased the percentages of asparagine and glutamine within the free amino acid pool; potassium was more effective than sodium. In 1970, sodium alone had little effect on the percentage distribution of free amino acids.Under conditions of severe potassium deficiency sodium can substitute to some extent for potassium in its effects on yields, solcble cartohydretcs acd various N fractions.
In a glasshouse experiment Italian ryegrass S 2 2 grown for g 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 NH,+-N or NO,--N. Tops grew best at 19-5" and with NO,--N yields were greatest a t IOO p.p.m. and with NH,+-N a t 200 p,p.m. Increasing NO,--N above 200 p.p.m. greatly decreased growth but increasing NH,+-N did not. At IOO p.p.m., NO,--N gave better yields than NH,+-N but a t 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 a-amino-N much less in grass given NO,--N than in grass supplied with NH4+-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 ; a t I I' soluble carbohydrates decreased with increasing level of N, more with NH4+-N than NO,--N. The causes of nitrate-N accumulation in grass are discussed.
Italian ryegrass (Lolium multiflorum) S22, grown in a greenhouse in K-deficient soil in pots, was given 40,SO and 160 mg of N/kg of soil (as ammonium nitrate) and 0, 60, 120 and 240 mg of K/kg of soil (as potassium chloride). In grass grown without added K, increasing N fertiliser increased the concentrations of total N, non-protein-N, ammonium-N, nitrate-N, free amino acids, amides and amines. With adequate K fertiliser all these N fractions decreased.The percentage distribution of N in the free amino-acid pool varied with the amount of N and K given. Without K fertiliser, increasing N had no consistent effect on most amino acids and amides, although it decreased the percentages of alanine and ethanolamine. Increasing K had relatively little effect on the percentage distribution in grass given the two smaller amounts of N. However, in the grass given the largest amount of N, it increased the percentage of most amino acids, especially alanine and 4-amino-n-butyric acid, and decreased glutamine and asparagine. p-Alanine was found only in K-deficient plants.The effect of K in relation to N metabolism and the nutritive value of herbage is briefly discussed.
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