Rooting depths are specified under the Manage Input Data > Crops section. The values indicate the rooting depth attained at different times of the calendar year.  A good source of root depth values is a local agricultural experiment station.  Use a value of 3 to 4 cm for the fallow periods to reflect the soil depth from which water will be evaporated in the absence of a crop.

 

Maximum depth for the majority of feeder roots for various crops are presented in Table 1.  Root depths are affected by many factors including the presence of chemical and physical barriers such as a clay pan or acid subsoils.  Figure 1, shows the relationship for corn root depth vs. time after planting for a soil without noted physical or chemical barriers.  For the water table management mode (and a reliable water source), root depth can be maintained at a much lower value and not affect production substantially.  Use of the 60 percent line for corn on Figure 1 has generally been successful in use of the model.  In general the effective root depth to be used in the model should be less than the values given in Table 1.  Furthermore it should be input as a function of time after planting.  Methods for estimating the change in root depth with time are discussed in the Reference Report (Skaggs, 1980).

 

Table 1 . Plant feeder root depths* (from Sprinkler Irrigation Handbook, Rain Bird Mfg. Corp., Glendora, California).

 

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Crop                Root depth                                Crop                                Root depth

 

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Alfalfa                3 to 6 feet                        Nuts                                3 to 6 feet

Beans        2 feet                                        Onions                        1 1/2 feet

Beets,Cane                2 to 3 feet                        Orchard                        3 to 5 feet

Berries                3 feet                        Pasture, grasses only        1 1/2 feet

Cabbage                1 1/2 to 2 feet         

Carrots                1 1/2 to 2 feet                Pasture                        2 feet

Corn (with clover)2 1/2 feet

Cotton                4 feet                        Peanuts                        1 1/2 feet

Cucumber                 1 1/2 to 2 feet                Peas                                2 1/2 feet

Grain                        2 to 2 1/2 feet                        Potatoes                2 feet

Grain,Sorghum        2 1/2 feet                        Soybeans                        2 feet

Grapes                3 to 6 feet                        Strawberries                1 to 1 1/2 feet

Lettuce                1 foot                        Sweet Potatoes                1 to 1 1/2 feet

Melons                2 1/2 to 3 feet                Tobacco                        2 1/2 feet

                                                 Tomatoes                        1 to 2 feet

 

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*Majority of feeder roots.

 

 

Figure 1.  Relationships for depth above which 50, 60, 70, and 80 percent of the total root length

exists versus time after planting for corn.  From data given by Mengel and Barber (1974).