Nutrient Cycling: Quiz

'Slash and burn' is a common subsistence farming system in many of the world's tropical regions. It involves manually clearing a small patch of rainforest and burning the fallen timber, prior to planting annual crops.

Answer the following question about this practice by selecting the two statements you think is most correct...

Growth of crops in subsequent years is

dependent on the fertility of the soil, and the nutrients lost each year through harvesting

always good because rainforest soils are extremely fertile

good because of the nutrient enrichment provided by the initial burn

likely to decline over time

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Yes, if the soil is initially very fertile and nutrient losses due to harvesting are limited, good growth of crops may be sustained for many years. If, however, the soil is poor and/or nutrient losses due to harvests are extensive, productivity may decline appreciably over time. Answer (d) is also correct.
No, not all rainforest soils are intrinsically fertile, on Fraser Island for example rainforests have developed on pure sands and all nutrients are tied up either in the biomass or the soil organic matter. Unless the soil is very fertile, nutrient losses due to the original burning and through harvests in subsequent years will result in a loss of productivity over time.
No, while the nutrient enrichment provided by burning may persist for a few years, nutrient losses due to the burning and harvesting will compound to reduce productivity over time.
Yes, nutrient losses due to burning and harvesting will compound, reducing soil fertility. Unless the soil is very fertile, this will lead to a reduction in productivity over time. Answer (a) is also correct.