No abstract

In pot experiments with greatly differing rates of N, P, K, and S, and 3 levels of water, dry matter (DM) yields of tubers varied from 28 to 454 g/pot. Especially P-, K- and S-deficiency reduced the starch content of boiled potatoes, from P from 74 to 59% in DM. S-deficiency increased soluble, insoluble and total digestible fibre (TDF) from about 9 to 12.4% TDF in DM of boiled potatoes. Lignin content of fresh potato DM was increased from 0.7 to 2.0 and from 0.8 to 3.7% by P- and K-deficiency. P-deficiency considerably increased arabinose, galactose, and uronic acid, and decreased glucose content. N-application and P-, K- and S-deficiency increased total- and NO3-N concentrations which varied from 1.32 to 3.67% and from 17 to 400 ppm in DM. Water stress slightly decreased total-N content. Increasing N in DM, due to high N-rates or P- or K-deficiency, decreased concentrations in crude protein (CP) of all essential amino acids, whereas aspartic acid (asparagine) increased. S-deficiency caused particularly strong decreases in concentrations of essential amino acids from 1.28 to 0.49, 1.62 to 1.10, 5.24 to 3.68, and 5.59 to 2.57 g/16 g N of cystine, methionine, lysine and leucine, respectively. Glutamic acid (glutamine) content was increased from 15.7 to 27.6 g/16 g N by S-deficiency. Expressed as g amino acid/kg DM, all amino acid concentrations increased with increasing % N in DM. In N-balance trials with rats, increasing crude protein concentrations in DM of boiled potatoes increased the true digestibility (TD) of the protein from 72 to 90 but decreased the biological value (BV) from 89 to 65. S-deficiency caused a further reduction of the BV to 45. Excluding S-deficiency treatments, linear regression equations between CP concentrations and BV and TD gave correlation coefficients r of -0.94*** and 0.82***, respectively. There was close agreement between changes of BV and concentrations of first limiting amino acids (chemical score), with r = 0.96***.

No abstract

Potatoes were grown in pots and fertilised with varying amounts of nitrogen (as nitrate or ammonium sulphate or urea), phosphorus, potassium and cow manure. The largest yield, 451 g D M per pot, was obtained with nitrogen in the form of urea. N-applications and P-and K-deficiency in the soil increased the total-N content, which varied from 1.14-3.07%. Concentrations of nitrate-N (0.001-0.016 %) were negligible. Increasing N-concentrations were associated with decreases in the crude protein of most amino acids including lysine (6.264.17 %), threonine (4.08-2.90 %), methionine (1.98-1.46 %) and tryptophan (1.74-0.86 %). The concentrations of aspartic and glutamic acids (probably mainly present as their amides) increased. Differences in amino acid composition between boiled and unboiled potatoes were negligible. From 70 to 90% of the decrease in concentration of most essential amino acids could be accounted for by changes in N-content of dry matter. Phosphorus and potassium affected the amino acid composition indirectly through their effects on N-content. In rat feeding experiments increasing N-concentrations in potatoes increased the true digestibility of the crude protein from 79 to 91 but decreased the biological value from 82 to 59. The net protein utilisation did also decrease (from 67 to 54). These relationships were linear below 2.2% N in dry matter. Changes were mainly dependent on variations in N-content. Decreases in essential amino acid indices or chemical scores were closely reflected in the results of the feeding experiments. The true amino acid digestibilities were different for individual amino acids and increased with increasing N-concentration in dry matter.

Zn pot experiments dry matter yield of seed of Vicia faba was increased by increasing application of S at all N-and P-levels and, by P at all S-and N-levels. Significant interactions were found for PxN (0.1 %) and SxP ( I %). N-concentrations generally increased with S-additions, but decreased with large applications of N and P . Significant interactions were found for PxN (0.1 %) and SxP (5%) with regard to N concentration. Maximum increases in cystine and methionine contents from Supplication were respectively 39.1 and 13.7% expressed as % of dry matter and 37.9 and 12.3% expressed as 8/16 g N . Highly significant correlation coeficients were obtained between concentrations (g/16 g N ) of a number of protein amino acids in seeds and total-N content. In a feeding trial with rats, the biological value of non-S treated seed was 40.8 and increased to about 60 in seed from Streatments. Addition of synthetic cystine and methionine to seed from the non-S treatment could not entirely substitute these acids present in the protein of seed from S-treatments with regard to effects on the biological value of seed protein.