diff --git a/src/morphology/root.jl b/src/morphology/root.jl
index 2d4c61f..b570767 100644
--- a/src/morphology/root.jl
+++ b/src/morphology/root.jl
@@ -62,6 +62,7 @@
     "Specific root length"
     SRL => 20 ~ preserve(parameter, u"cm/g")
 
+    # From CROPGRO
     "Root length density"
     RLD(WR, soil_depth, SRL) => WR / soil_depth * SRL ~ track(u"cm/cm^3")
 end
\ No newline at end of file
diff --git a/src/physiology/nitrogen.jl b/src/physiology/nitrogen.jl
index df88a96..645d838 100644
--- a/src/physiology/nitrogen.jl
+++ b/src/physiology/nitrogen.jl
@@ -77,11 +77,11 @@
     "Relative drought factor"
     drought_factor(ASW, minASW, field_capacity, maxASW) => begin
         if ASW > field_capacity
-            2.0 - (ASW - field_capacity) / (maxASW - field_capacity)
+            1 - (ASW - field_capacity) / (maxASW - field_capacity)
         else
-            2 * ((ASW - minASW) / (field_capacity - minASW))
+            ((ASW - minASW) / (field_capacity - minASW))
         end
-    end ~ track(min=0, max=1) 
+    end ~ track(min=0.1, max=1) 
 
     # Nitrogen uptake conversion factor.
     # How much kg/ha of nitrogen for mg/cm of nitrogen (root)?
diff --git a/src/rhizosphere/waterbalance.jl b/src/rhizosphere/waterbalance.jl
index 740d945..811903f 100644
--- a/src/rhizosphere/waterbalance.jl
+++ b/src/rhizosphere/waterbalance.jl
@@ -43,7 +43,8 @@ Transpiration
     #     ((Int(soil_class) > 0) ? (11 - 2 * Int(soil_class)) : (SWpower0))
     # end ~ preserve
 
-    field_capacity(maxASW) => 0.5 * maxASW ~ preserve(u"mm")
+    fc => 0.5 ~ preserve(parameter)
+    field_capacity(fc, maxASW) => fc * (maxASW + minASW) ~ preserve(u"mm")
 
     "Proportion of rain intercepted"
     interception(LAI, maxInterception, LAImaxInterception) => begin