Cropping system sensitivity to climate change in northern Laos
Within a context of rapid transition from subsistence to commercial agriculture, cropping systems in northern Laos have to cope with climate change. The objective of this study was to describe the sensitivity to climate change of four major annual crops cultivated in Luang Prabang Province, northern Laos: upland rice (one glutinous local variety), maize (one hybrid and one local variety), and job's tear (one local variety).
First, farmers were interviewed to document the main cropping systems: cultivated cultivars, crop cycles, cropping patterns, yield ranges etc. Field measurements were made to collect additional information on soils (e.g. depth, water holding capacity) and crops (e.g. leaf area index). Data collected were used to calibrate a simple agroclimatic model, called Potential Yield Estimator (PYE), to simulate plant growth and yields under potential and water-limited conditions. 16 years daily climatic data (1985-2000) and yield data were used to test model accuracy. Several virtual experiments were conducted to assess input parameters (e.g. water runoff, soil water holding capacity, sowing date) influence on plant growth and yields. Cropping system sensitivity to climate change was assessed considering current scenarios of climate change for the area. Changes in crop potential yield were estimated according to sowing date.
The analysis of water-limited yield and its sensitivity to runoff and soil properties revealed an optimum sowing window for which water limited yield is close to potential yield, and for which interannual variability is low. Water-limited yield is little sensitive to runoff but its sensitivity (average decrease in yield and interannual variability) to soil depth and soil water holding capacity is increasing when sowing dates depart from optimum sowing windows. Climate change could decrease crop potential yields but should not affect critically the relative water-limited yield and its variability related to soil properties and runoff. Drainage, another output of the model, is expected to
increase with climate change, which lead to question the current trend of using fertilizers to cope with fertility losses and fallow-period shortening.