WATER STRESS?? -- Pure stand & Intercrops

Pure Stand Model

This model simulates whether water stress was encountered by a crop grown in pure stand. Field observations on LAI-development or fraction absorbed radiation serve as input to the model. The model simulates the daily (and cumulative) values of absorbed radiation, transpiration and dry matter production. In the model, a soil moisture balance is tracked, with precipitation as input and transpiration and percolation as output. The soil profile is composed of two layers: a rooted zone of fixed size and the zone below. The water module follows the tipping bucket principle: if water holding capacity in the rooting zone is reached, additional water input percolates to the next zone. If soil moisture content drops below a critical level, the transpiration is reduced and potential transpiration is not fulfilled. Dry matter production is then reduced with a ratio of actual over potential transpiration. Next to LAI or fraction absorbed radiation, the model makes use of other crop and site specific information. These include: Crop/canopy characteristics (light extinction coefficient, RUE, transpiration coefficient, rooting depth, soil depletion factor), Soil characteristics (rooting depth, field capacity, wilting point), and Weather characteristics (daily values of global radiation and precipitation).

Intercrops Model

This model simulates whether water stress was encountered by the component crops of a mixture. Field observations on LAI-development or fraction absorbed radiation serve as input to the model. The model simulates the daily (and cumulative) values of absorbed radiation, transpiration, and dry matter production for the two component species. Total incoming radiation is distributed over the two species, based on plant height, LAI and light extinction coefficient of the two species. The canopy is dissected in two layers. The top layer ranges from the maximum height of the tallest species, till the maximum height of the shortest species. The bottom layer ranges from the top of the shortest species till ground level. The vertical distribution of the LAI of both species is assumed to be homogeneous. Light interception is calculated using Beer's law. First, for the top layer which consists of just one species. The light that is transmitted through the first layer serves as input to the second layer, which consists of two species. In this layer, first, the light interception by both species combined is calculated and then the intercepted light is distributed over the two species based on the product of k*LAI. Dry matter production is calculated using a species-specific RUE. The amount of newly produced dry matter is used to calculate the potential transpiration, using a species-specific transpiration coefficient. In the model, a soil moisture balance is tracked, with precipitation as input and transpiration and percolation as output. The soil profile is composed of three layers: a first zone till maximum rooting depth of the species with shortest rooting depth, the second layer till maximum rooting depth of the other species and the zone below. The water module follows the tipping bucket principle: if water holding capacity in the first rooting zone is reached, additional water inflow percolates to the second zone. If this zone has also reached its maximum water holding capacity, water will flow to the next zone, out of reach for the roots of either of the two species. If soil moisture content drops below a critical level for a species, the transpiration is reduced and potential transpiration is not fulfilled. This soil moisture depletion factor is crop specific. Transpiration requirement of the species with the deepest rooting system is distributed over the two rooting zones, in proportion to the depth of the two layers. If transpiration of the first layer cannot be completely met, this amount will be added to the requirement of the second layer. If actual transpiration is insufficient to meet the potential transpiration demand of a species, the dry matter production is reduced with a ratio of actual over potential transpiration. Next to LAI or fraction absorbed radiation, the model makes use of other crop and site-specific information. These include: Crop/canopy characteristics (light extinction coefficient, plant height, RUE, transpiration coefficient, rooting depth, soil depletion factor); Soil characteristics (rooting depth, field capacity, wilting point); and Weather characteristics (daily values of global radiation and precipitation).