Nutrientcycling is generally quite conservative

In contrast to ecosystems that are not harvested (e.g., native forest, grasslands), where in nutrientcycling is generally quite conservative, most agriculturalecosystems are net exporters of nutrients inherent in soil. Consider the following barley production system:

— Soilcontains 0.5% “available” Ca in the rooting zone to adepth of 50 cm.
—  Soil bulkdensity is 1.20 g/cm3.
— Totalplant production (above ground biomass) is 5000 kg/ha/yr(dry-weight basis).
— Totalgrain yield is 2500 kg/ha/yr (dry-weight basis).
— Ca contentof the grain is 0.05%.
—  Ca contentof the whole above ground plant is 1.5%.

1 ha = 10,000 m2

a) If only the grain is removed fromthe field, how many years will the “available” Casupply in the soil last (assuming yields don’t decrease as Cacontent decreases)?

b) If the entire barley plant isremoved, how long will the Ca last (same assumption as above)?

c) Speculate upon and briefly discussimplications for barley straw and soil fertility management inlight of the results from a) and b) above.

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