Changes In Agroecosystems Research Articles

Agricultural Change as an Incremental Process

Abstract At least two major views of agro-ecosystem change can be recognized–systematic and incremental. Systematic change involves the addition of new fields and associated features that are constructed completely prior to cultivation; incremental change involves gradual transformation of fields and features in conjunction with cultivation. The systematic view has been the more dominant of the two, particularly as applied to interpretations of past agro-ecosystems. Using present-day data on temporales or runoff-dependent fields in eastern Sonora, Mexico, this study describes one case of incremental agro-ecosystem change. Small, individual fields are developed into a more complex system by progressive modification resulting from the cumulative actions of individual farmers. In this case, the resulting constructional form of the agro-ecosystem alone does not allow assessment of the process of its development. Interpretations of past agro-ecosystems should recognize that both change processes are possible.

Soil nutrient status of hill agro-ecosystems and recovery pattern after slash and burn agriculture (Jhum) in north-eastern India

The present study deals with fertility changes in agro-ecosystems where vegetation is removed by slash and burn procedures, the land is planted to crops (cultivated) for one year, and then left to revegetate naturally for upto 50 years (forested fallow, here after referred to as ‘fallow’) before the entire cycle (locally called ‘Jhum’) is repeated. A comparison has been made between three jhum cycles of 30, 10 and 5 years. Depletion in soil carbon continued throughout the cropping period of one year and extended upto a 5 year fallow. This could be one of the reasons against a short jhum cycle, alongwith a similar pattern in depletion of nitrogen. Available phosphorus build up in the fallows also starded only beyond a 5 year fallow period with rapid increase in 10, 15 and 50 year fallows. Cationic concentration in the soil also rapidly declined in the early phases of regrowth of vegetation. This decline was most pronounced for potassium due to the fact thatDendrocalamus hamiltonii is a heavy accumulator of this nutrient. Since this bamboo species dominates the fallow upto about 20 years, potassium build up in the soil was observable only at this stage. It is suggested that this species plays an important role in conservation of this nutrient. In a 50 year fallow, low levels of calcium and magnesium were maintained with rapid depletion of both with depth which is in contrast to that of potassium and phosphorus. In general, short jhum cycles of 5 year permit only low levels of soil fertility with very poor recovery during the fallow period. The significance of these results are discussed.