Implement crop rotation in SWAT

[John Yumbya]

Dear SWAT users,

I would like to implement crop rotations in ArcSWAT.

I've three crops planted different times in the year. How do I assign the initial land uses before adding the rotations in the management file? Or does SWAT allow planting of only one crop in a year?

Regards,

-John

[charlesi @iastate.edu]

John,

If you "do nothing," SWAT will assume the crop/plant that is associated with the land use.  To enter a rotation, you have to use the Operations Management menu in the .mgt.  I think complex rotations are easier to simulate by date rather than by heat units.  You lose some realism but you gain certainty that you get the crop planted, growing, and harvested.  I have pasted a table with an example rotation below.  The right-most 2 columns you don't need to worry about.  This was just to help me keep track of the actual N and P applied (the SWAT input is the fertilizer amount).  The table below is for a 6-year rotation of soybeans - corn - alfalfa - alfalfa - alfalfa - corn.  After 6 years, it repeats at the first year and runs through all six again.  There's no reason you can simulate multiple crops in the same year, just be sure to get the correct kind of harvest/kill.  Harvest implies biomass/grain removal.  Kill implies the crop dies and all residue/biomass remains. 

				Fertilizer	N	P2O5
Year	Month	Day	Operation	KG/HA	KG/HA	KG/HA
1	4	15	Fert (ComP)	198	31.68	95.04
1	5	1	Plant SOYB
1	9	30	Harvest/kill
1	10	25	Fert (anhyd)	50	41
2	4	15	Fert (anhyd)	73	59.86
2	4	15	Fert (UAN)	85	28.05
2	5	1	Plant CORN
2	9	30	Harvest/kill
3	1	1	Plant ALFA
3	6	7	Harvest
3	7	17	Harvest
3	8	26	Harvest
3	10	1	Fert (ComP)	118	18.88	56.64
3	12	1	Kill
4	1	1	Plant ALFA
4	6	7	Harvest
4	7	17	Harvest
4	8	26	Harvest
4	10	1	Fert (ComP)	118	18.88	56.64
4	12	1	Kill
5	1	1	Plant ALFA
5	6	7	Harvest
5	7	17	Harvest
5	8	26	Harvest
5	10	1	Fert (ComP)	118	18.88	56.64
5	12	1	Kill
6	4	15	Fert (anhyd)	73	59.86
6	4	15	Fert (UAN)	85	28.05
6	5	1	Plant CORN
6	9	30	Harvest/kill

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[Narayan Shrestha]

Dear Charles,

How to assign the year in mgt file? In the SWAT input-output document, there is no space for adding year values as the spaces allocated for the month is columns 2-3.

Also, for trees, do you have example mgt file? I mean, what should be the typical year of rotation, and other management operation values? For sure, the year of rotation >1, which made other management operation tricky as the year need to be specified in the operation.

Regards,
Narayan