Features of the growth and mineral nutrition of Noogoora burr (Xanthium occidentale Bertol.), a noxious weed in central New South Wales

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Abstract
Aspects of the growth and accumulation, partitioning and redistribution of selected minerals in the weed Xanthium occidentale (Noogoora burr) are described for a population from central New South Wales. Plants required 240 days from emergence to fruit maturity. Uptake of most elements occurred until midway through fruit development. Rates of nutrient intake by roots were similar to those of some crop species. Fruits made up of 46% of the dry matter of a mature plant and contained 58- 79 % of its P, N and S, 18-39 % of the Cl, Na, Mg and K, but < 19 % of the Ca and Mn. Dead leaves had the greatest proportion of the total plant Mg, Na, Cl, and especially Mn and Ca. The elements P, N and S were redistributed from above-ground parts to the fruits with efficiencies of 43-63 %, but there was negligible (< 10%) redistribution of Cl, Mn, Ca and Na. Redistribution from above-ground plant parts could have provided 43-55 % of the dry matter, N, P, K, S and Mg accumulated by fruits. The amount of free nitrate-N stored in stems and leaves decreased rapidly during fruit filling. Leaves were more important than stems as a source of nutrients for redistribution, but the stem was more important for redistribution of dry matter. Cotyledons of parent seeds redistributed dry matter and nutrients to seedlings with net efficiencies ranging from 16-97 %, but gained Cl and Ca. Redistribution from cotyledons provided 2-45 % of the amount of a nutrient accumulated by seedlings. Seeds made up 38 % of the fruit dry matter and had 60-93% of its S, P and N, but only small proportions of its Ca, Cl, Na and Mn. Seeds had 38% protein and 39% oil. It is concluded that the high capacity of Noogoora burr to accumulate reserves of nutrients for redistribution to fruits contributes to its success as a weed.