CropSyst Training Course, Piracicaba, Brasil, 2010 Water Balance in CropSyst Marcello Donatelli CRA-ISCI, Italy Claudio Stockle BSE, Washington State University,

Apresentação em tema: "CropSyst Training Course, Piracicaba, Brasil, 2010 Water Balance in CropSyst Marcello Donatelli CRA-ISCI, Italy Claudio Stockle BSE, Washington State University,"— Transcrição da apresentação:

1 CropSyst Training Course, Piracicaba, Brasil, 2010 Water Balance in CropSyst Marcello Donatelli CRA-ISCI, Italy Claudio Stockle BSE, Washington State University, USA

2 CropSyst Course, 2010, Piracicaba, Brasil CropSyst Course, 2010, Piracicaba, Brasil Modelling the Water Balance Precipitation Irrigation Shallow water table Interception Runoff Percolation Evaporation Transpiration Input: Output: dW dt = Pr + Ir + Wt - In - Ro - Pe - Ev - Tr

3 CropSyst Course, 2010, Piracicaba, Brasil CropSyst Course, 2010, Piracicaba, Brasil Inputs in the Water Balance Precipitation amounts are obtained from weather input files; they can be partially intercepted by both the crop and surface crop residues. Irrigation can be set in the management files as a fixed-date event or as automatic irrigation. The supply of water from the water table is obtained by setting a saturated bottom boundary to the soil profile at a user-specified depth (available only for the finite difference water transport solution).

4 CropSyst Course, 2010, Piracicaba, Brasil CropSyst Course, 2010, Piracicaba, Brasil Runoff Runoff is estimated using: the SCS/USDA curve number method. a modeling of soil surface retention In the SCS/USDA method, the main variables affecting the runoff estimate are the soil water content in the upper 1 meter (weighted by depth), the field slope, and the curve number. The curve number is automatically selected from other inputs such us soil texture, hydrologic condition, hydrologic group, land use, and selected management practices.

5 CropSyst Course, 2010, Piracicaba, Brasil CropSyst Course, 2010, Piracicaba, Brasil Water Redistribution The water which is neither intercepted by the crop and crop residues, and which do not runoff infiltrates the soil. Two methods are available to simulate water redistribution in the soil profile : The capacity method (or cascading) The finite difference method to solve Richard’s equation

6 CropSyst Course, 2010, Piracicaba, Brasil CropSyst Course, 2010, Piracicaba, Brasil The Capacity Method The capacity methods is implemented by subdividing the soil profile in 10 cm (or less) layers. Water moves downward from the soil surface filling each layer up to field capacity; the amount of water exceeding moves to the lower layer and finally percolates out of the soil profile. The is no capillary raise and the maximum water content simulated is the one corresponding to field capacity.

7 CropSyst Course, 2010, Piracicaba, Brasil CropSyst Course, 2010, Piracicaba, Brasil The Finite Difference Method The method is a numerical solution of Richard’s equation for water flux in the soil. Some of the parameters needed by the method, such as saturated hydraulic conductivity and the hydraulic conductivity curves, are estimated by the program based on soil parameters provided. The soil water content can reach saturation and the methods allows for upward water flow.

8 CropSyst Course, 2010, Piracicaba, Brasil CropSyst Course, 2010, Piracicaba, Brasil Potential Evapotranspiration Potential evapotranspiration is estimated using two methods: Penman-MonteithTx, Tn, Rad, Wind, Hx, Hn Priestley-Taylor *Tx, Tn, Rad data needed * according to Steiner et al.

9 CropSyst Course, 2010, Piracicaba, Brasil CropSyst Course, 2010, Piracicaba, Brasil Partitioning Potential Evapotranspiration Potential evapotranpiration is partitioned into potential transpiration and potential evaporation as a function of crop LAI and of crop light extinction coefficient. The latter sets the amount of radiation intercepted by the crop.

10 CropSyst Course, 2010, Piracicaba, Brasil CropSyst Course, 2010, Piracicaba, Brasil Soil Evaporation Evaporation conventionally occurs only in the upper 5 cm of soil (evaporative layer) The cascading approach for water redistribution does not account for water upward movements, so evaporation occurs only with water which infiltrates the first layer from the surface Evaporation proceeds at the potential rate until the permanent wilting point is reached. Then potential evaporation decreases according to a linear function of water content, reaching zero at a water content of 1/3 of the permanent wilting point (air dry soil)

11 CropSyst Course, 2010, Piracicaba, Brasil CropSyst Course, 2010, Piracicaba, Brasil Crop Transpiration Crop transpiration is the minimum between the atmospheric demand and soil water supply The demand is set by the fraction of the potential evapotranspiration (potential transpiration) times the ET coefficient The supply is set by the available soil water in the root zone

12 CropSyst Course, 2010, Piracicaba, Brasil CropSyst Course, 2010, Piracicaba, Brasil Modelling Crop Water Uptake The rate of water loss from a crop is determined by the resistance to vapor flow from the crop to the atmosphere Since, on average, water loss cannot exceed uptake, the plant must exercise some control over resistance to vapor loss so that uptake and loss can be balanced A simple model for uptake and loss has been adopted for daily time step simulations

13 CropSyst Course, 2010, Piracicaba, Brasil CropSyst Course, 2010, Piracicaba, Brasil Modelling Crop Water Uptake ss ssss ssss ssss ssss  xr  xl  l1  l2  l3  l4 llll

14 CropSyst Course, 2010, Piracicaba, Brasil CropSyst Course, 2010, Piracicaba, Brasil Crop Water Uptake U = C p (  s -  l ) U = Crop water uptake (kg m -2 s -1 ) C p = Plant hydraulic conductance (kg s m -4 )  s = Soil water potential (J kg -1 )  l = Leaf water potential (J kg -1 )

15 CropSyst Course, 2010, Piracicaba, Brasil CropSyst Course, 2010, Piracicaba, Brasil Maximum Plant Hydraulic Conductance Maximum plant hydraulic conductance can be estimated as the conductance of a crop completely covering the ground and transpiring at the maximum rate. U max = C pmax (  fc -  l,s )

16 CropSyst Course, 2010, Piracicaba, Brasil CropSyst Course, 2010, Piracicaba, Brasil Actual Plant Hydraulic Conductance Actual plant hydraulic conductance can be determined from the maximum value times the fraction of incident radiation intercepted by the crop canopy C p = C pmax f int

17 CropSyst Course, 2010, Piracicaba, Brasil CropSyst Course, 2010, Piracicaba, Brasil Actual Crop Transpiration  How much will a crop transpire in a given day? The minimum between U max and TR p, if soil water is not limiting