Growth of seedlings of pasture grasses and legumes deprived of single mineral nutrients.
The effective internal supply of specific nutrient elements in the seeds of 7 grass and 5 legume pasture species was quantified by growing newly germinated seedlings in nutrient solutions each deficient in 1 element (N, P, K, Ca, Mg, Fe or S). The DW attained in 3 weeks was taken as a measure of the availability for seedling growth of each element. In aggregate, the order in which the element deficiencies limited growth was N (most limiting), K, Mg, P, Fe, Ca and S. The grasses and legumes gave similar responses except to Ca for which the legumes had a markedly greater requirement. No significant correlations were found between the concn of individual elements in the seeds and the mineral requirement of seedlings. Only for P was there a significant correlation between the absolute amount per seed and the seedling requirement. Sequential harvesting of Lolium perenne and Trifolium repens seedlings at 2-day intervals showed that the order in which the elements became limiting was positively correlated with the order of requirement based on the DW of 3-week-old seedlings. Overall, the results indicated that chemical analysis of seeds did not provide a useful measure of the mineral resources available for seedling growth, that the usable mineral nutrients were markedly unbalanced in relation to seedling requirements and that taxonomically unrelated species behaved in a broadly similar way.