Crop Rotation in sustainable farming

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Problem definition

Crop rotation is based on growing a series of different types of crops in the same area in sequential seasons. The planned rotation may vary from a growing season to a few years or even longer periods. It is one of the most effective agricultural control strategies that is used in preventing the loss of soil fertility. It also helps in reducing soil erosion and increases crop yield. Planning an effective crop rotation requires weighing fixed and fluctuating production circumstances: market, farm size, labor supply, climate, soil type, growing practices, etc.

In this simulation I will try to find parameters which have impact on the whole process of crop rotation with goal to find model providing desired outputs (these were slightly changed from concept) - crop yields, greenhouse gas emissions (N2O, CO2, NH4), soil fertility (nitrogen levels).

I will focus on four crop rotation strategies with three different crops - corn, soybean, wheat:

CCC (continuous corn) - only corn will be farmed for the whole observed time period (40 years)

CS (corn-soybean) - rotation of corn and soybean will be used in year cycles for the whole observed time period (40 years), first year corn, second year soybean, repeat..

SSS (continuous soybean) - only soybean will be farmed for the whole observed time period (40 years)

CSW (corn-soybean-wheat) - rotation of corn, soybean and wheat will be used in year cycles for the whole observed time period (40 years), first year corn, second year soybean, third year wheat, repeat..

Goal of this simulation is to observe dynamic changes with yields, greenhouse gas emissions, tillage strategy and soil nitrogen levels, while changing different crop rotation strategies.

Method

Vensim modelling approach was selected due to dynamic behavior of the simulated system.

Model

Variables

Number of rotated crops

Input constant variable which can be changed based on crop strategy. Range <1,3>.

=1 (in case of CCC and SSS strategies)

=2 (in case of CS strategy)

=3 (in case of CSW strategy)

Corn production

PULSE TRAIN function ensures specific crop to be delivered by time pattern. In crop rotation strategies, if corn is present, it is always first crop, therefore it starts at time 0 (first year), duration is 1 year, repetition is based on number of crops (eg. 2 - it repeats in third year) and final time is set to fixed 40 years according to simulation setup.

=Corn quantity*PULSE TRAIN(0, 1 , Number of rotated crops ,40)

Soybean production

Similar case as in Corn production variable only with difference of initial year, if sobyean is present in crop rotation strategy, it is always second crop, therefore it starts at time 1 (second year). In case of SSS strategy it starts at time 0 (first year)

=Soybean quantity*PULSE TRAIN(IF THEN ELSE(Number of rotated crops=1, 0 , 1 ), 1 , Number of rotated crops , 40 )

Wheat production

Similar case as in Corn production variable only with difference of initial year, if wheat is present in crop rotation strategy, it is always third crop, therefore it starts at time 2 (third year).

=Wheat quantity*PULSE TRAIN(2, 1 , Number of rotated crops , 40 )

Corn quantity

Input constant variable which can be changed based on crop strategy. Range <0,100>.

=100 (in case of CCC, CS and CSW strategies)

=0 (in case of SSS strategy)

Soybean quantity

Input constant variable which can be changed based on crop strategy. Range <0,40>.

=40 (in case of CS, SSS and CSW strategies)

=0 (in case of CCC strategy)

Wheat quantity

Input constant variable which can be changed based on crop strategy. Range <0,80>.

=80 (in case of CSW strategy)

=0 (in case of CCC, CS, SSS strategies)

increase of N2O emissions

Auxiliary variable which changes based on each crop production and its emission coefficient (pattern was extracted from a study),additionaly it changes slightly according to tillage strategy and usage of extra inorganic fertilizer.

Corn production*Corn N2O emission coef*IF THEN ELSE(Tillage=0, 1.5 , 1.4)+ Soybean production*Soybean N2O emission coef*IF THEN ELSE(Tillage=0, 1.5 , 1.4)+ Wheat production*Wheat N2O emission coef*IF THEN ELSE(Tillage=0, 1.5 , 1.4)+ Inorganic fertilizer/5

increase of CO2 emissions

Similar auxiliary variable as increase of N20 emissions extra except zero effect with inorganic fertilizer.

Corn production*Corn CO2 emission coef*IF THEN ELSE(Tillage=0, 3 , 2.9)+Soybean production*Soybean CO2 emission coef*IF THEN ELSE(Tillage=0, 3 , 2.9)+Wheat production

  • Wheat CO2 emission coef*IF THEN ELSE(Tillage=0, 3 , 2.9)

increase of CH4 emissions

Similar auxiliary variable as increase of N20 emissions extra except zero effect with inorganic fertilizer.

Corn production*Corn CH4 emission coef*IF THEN ELSE(Tillage=0, 0.3 , 0.2)+Soybean production*Soybean CH4 emission coef*IF THEN ELSE(Tillage=0, 0.3 , 0.2)+Wheat production

  • Wheat CH4 emission coef*IF THEN ELSE(Tillage=0, 0.3 , 0.2)

Cumulative N2O emissions

Cumulative CO2 emissions

Cumulative CH4 emissions

Corn N2O emission coef

Soybean N2O emission coef

Wheat N2O emission coef

Corn CO2 emission coef

Soybean CO2 emission coef

Wheat CO2 emission coef

Corn CH4 emission coef

Soybean CH4 emission coef

Wheat CH4 emission coef

Inorganic fertilizer

Soil nitrogen

increase of soil N

decrease of soil N

Soil nitrogen level

Temperature

Precipitation

Pests

Tillage

Natural disasters

increase of C yield

increase of S yield

increase of W yield

Corn yield

Soybean yield

Wheat yield

Total yield

=Corn yield + Soybean yield + Wheat yield

Results

Conclusion

Code

References