Abstract
Modelling of the effects of water and different levels of nitrogen on evapotranspiration and water productivity of rainfed soybeans is very important in optimising resource use in the production of the crop. The objective of the study was to model evapotranspiration, soil water storage and water productivity of rainfed soybeans under different levels of nitrogen fertilizer by using the FAO AquaCrop model. Field experiments were conducted at the Teaching and Research Farms of Obafemi Awolowo University, Nigeria in the rainy seasons of 2015 and 2016. There were five levels of nitrogen, which are 00, 25, 50, 75 and 100% of the recommended nitrogen applications and two varieties of soybeans, which produced a 2 by 5 factorial experimental design. The data of the wetter year 2015, were used for calibration of the AquaCrop model because AquaCrop is water driven. The 2016 data were used for the validation. The AquaCrop model simulated canopy cover with R2 and EF > 0.90, d-index ≥ 0.99. The model captured the trend of the soil water storage well, R2 and EF ≥ 0.70. The AquaCrop model simulated soil water storage below wilting point for seasonal rainfall less than 600 mm, and it did not overestimate it. The model predicted evapotranspiration with R2 and EF ≥ 0.89, d-index = 1.00. Above ground biomass was overestimated even though R2 ≥ 0.98. Although, nitrogen stress reduced seed yield and water productivity, there was no under or over estimation of the seed yields. They were predicted with low error under the different levels of nitrogen fertilizer, R2 ≥ 0.99, EF and d-index ≥ 0.99. The AquaCrop model is suitable for simulating canopy cover, soil water storage, evapotranspiration, and seed yield of rainfed soybeans with different levels of nitrogen fertilizer under temporal distribution of seasonal rainfall. Therefore, it can serve as a useful tool for smallholder farmers in predicting productivity of soybeans and optimising resource allocation, land and water use in the tropical farming systems. We recommend simulation of the effects of pest on biomass, seed yield and water productivity by subsequent versions of the AquaCrop model. In addition, incorporating an economic sub-unit in the model will enable users to make financial decisions.
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Claims 12
Claim · model-written summary
AquaCrop simulated canopy cover with high fit.
Verbatim
e0“The AquaCrop model simulated canopy cover with R2 and EF > 0.90, d-index ≥ 0.99.”
Claim · model-written summary
AquaCrop captured soil water storage trends well.
Verbatim
e0“The model captured the trend of the soil water storage well, R2 and EF ≥ 0.70.”
Claim · model-written summary
AquaCrop simulated soil water storage below wilting point with rainfall under 600 mm without overestimation.
Verbatim
e0“The AquaCrop model simulated soil water storage below wilting point for seasonal rainfall less than 600 mm, and it did not overestimate it.”
Claim · model-written summary
AquaCrop predicted evapotranspiration with high fit.
Verbatim
e0“The model predicted evapotranspiration with R2 and EF ≥ 0.89, d-index = 1.00.”
Claim · model-written summary
AquaCrop overestimated aboveground biomass.
Verbatim
e0“Above ground biomass was overestimated even though R2 ≥ 0.98.”
Claim · model-written summary
Nitrogen stress reduced seed yield.
Not reportedTaxonComparator
Verbatim
e0“nitrogen stress reduced seed yield and water productivity”
Claim · model-written summary
Nitrogen stress reduced water productivity.
Not reportedTaxonComparator
Verbatim
e0“nitrogen stress reduced seed yield and water productivity”
Claim · model-written summary
Seed yields were predicted without bias and with low error across nitrogen levels.
Verbatim
e0“there was no under or over estimation of the seed yields. They were predicted with low error under the different levels of nitrogen fertilizer, R2 ≥ 0.99, EF and d-index ≥ 0.99.”
Claim · model-written summary
Authors considered AquaCrop suitable for simulating rainfed soybean outcomes.
- Taxon
- soybeans
Glycine maxe0 - Outcome
- suitable for simulating canopy cover, soil water storage, evapotranspiration, and seed yielde0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“The AquaCrop model is suitable for simulating canopy cover, soil water storage, evapotranspiration, and seed yield of rainfed soybeans with different levels of nitrogen fertilizer under temporal distribution of seasonal rainfall.”
Claim · model-written summary
Authors proposed AquaCrop for farmer resource decisions.
- Taxon
- soybeansGlycine maxe0
- Outcome
- predicting productivity of soybeans and optimising resource allocation, land and water usee0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“it can serve as a useful tool for smallholder farmers in predicting productivity of soybeans and optimising resource allocation, land and water use in the tropical farming systems.”
Claim · model-written summary
Authors recommended simulating pest effects in future AquaCrop versions.
- Outcome
- simulation of the effects of pest on biomass, seed yield and water productivitye0
Not reportedTaxon
Verbatim
e0“We recommend simulation of the effects of pest on biomass, seed yield and water productivity by subsequent versions of the AquaCrop model.”
Claim · model-written summary
Authors proposed an economic component for financial decisions.
- Outcome
- incorporating an economic sub-unit in the modele0
Not reportedTaxon
Verbatim
e0“incorporating an economic sub-unit in the model will enable users to make financial decisions.”
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