Growth and nutrient accumulation of Brazil nut trees(Bertholletia excelsa) in agroforestry at different fertilizer levels

The Brazil nut tree（Bertholletia excelsa） is a frequent component of agroforestry systems in the Amazon because of its adaptation to nutrient-poor upland soils and multiple uses.We investigated the aboveground biomass production（kg dry weight）,nutrient uptake and requirements（N,P,Ca,Mg,K） of Brazil nut trees of different sizes grown under agroforestry conditions and fertilized at different levels.Eight of 70 experimental trees with different size were harvested and stem,branches and leaves were separated.Nutrient contents were determined for three trees of varying size.Average tree growth was fast,but variability was high,suggesting considerable potential for the improvement of this economically important species.The trees responded to increased levels of fertilizer and lime with significantly increased foliar nutrient contents and growth,probably because of the improved availability of Mg and Ca for which the species seems to have a relatively high demand.In contrast to Brazil nut trees grown in forest or dense plantations,the agroforestry trees invested a substantial part of their biomass and nutrients in large branches and developed spreading crowns.To improve stem form,reduce competition with associated crops for light and recycle nutrients,regular pruning of lower branches or planting arrangements that favor self-pruning are recommended.These measures would also increase the recycling of Ca and Mg,large quantities of which are contained in the branches.

Weed Competition Periods Affect Grain Yield and Nutrient Uptake of Black Seed(Nigella Sativa L.)

The combination of the relatively open plant canopy and slow growth,especially at early growth stages,results in lower competitiveness of black seed(Nigella sativa L.) than weeds.Thus,weed interference is known as an important factor affecting black seed yield.Therefore,to determine the critical period of weed control and its effects on nutrients uptake of black seed field experiments were conducted in 2011 and 2012.Two quantitative series of weed removal treatments including weed-infested and weed-free treatments were implemented from black seed emergence to maturity harvest.To determine critical period of weed control,plots were weed-infested or weed-free for 0,14,28,42,56,70 days after emergence,in weed-infested and weed-free treatments,respectively.The results revealed that N,P and K contents in weed tissues significantly increased with increasing weed-infested periods during both years of the experiment.The reduction in grain and oil yield due to longer periods of weed-infested conditions or shorter periods of weed-free conditions were accompanied by simultaneous reduction of N,P and K uptake in black seed grains and tissues.Overall,N,P and K contents in weed tissue were found to be 1.8 to 2 times higher than that of black seed.It was concluded that 58 or 49 days weed-free periods are required to avoid yield loss(above 5% or 10%) in black seed.