Abstract:
Linking nutrient balances and flows to soil
nutrient stocks creates a valuable indicator for sustainability
assessment in agricultural land-use systems.
Therefore, we investigated the impact of management
on soil fertility at farm/field scale using the Nutmon
approach. A detailed methodology for the adaptation
of the difficult-to-quantify flows to the local conditions
is described. Research was carried out in the three
farming systems of Yantzaza (low-external-input), El
Tambo (irrigated cash crops) and San Lucas (integrated
nutrient management) in southern Ecuador. For
each land-use within a farm (annual and perennial
crops, pasture, forest), soil nutrient balances and flows
were modeled with Nutmon and soil nutrient stocks
were calculated for NPK. Soil nutrient balances were
evaluated using potential socio-economic and soil
fertility explanatory variables. Balances for the different
land-uses in the three research areas varied between
-151 to 66 kg ha-1 a-1 for N, -4 to 33 kg ha-1 a-1 for P and -346 to 39 kg ha-1 a-1 for K and were mainly negative. Up to 70 % of the balances’ variability was explained by soil fertility variables and financial flows. Highest external inputs existed in
land-uses with a strong market orientation. Land-uses
benefiting from a surplus of within-farm flows had the
highest soil nutrient stocks. The focus on N fertilization
induced highly negative PKbalances in annual crops of
El Tambo. In contrast, the application of organic
fertilizers and nutrient recycling in San Lucas resulted
in positive NP balances particularly for perennial
crops. NP balances in annual crops of Yantzaza were
most negative due to nonexistent fertilization, leaching
and burning of crop residues. A non-sustainable landuse
of annual crops in Yantzaza was illustrated by total
N stock decreases of 4.9 % a-1 and decreased soil
organic carbon stocks to 85 % of adjacent forest sites.
Results indicated a potential risk regarding sustainable
management of soils in the research area and provide a
basis for policy and decision makers to develop
appropriate management strategies.
