Modelling the optimal phosphate fertiliser and soil management strategy for crops

James Heppell August 2014

My Research• The aim of my research is to model water and P uptake by crop roots

and to optimise a sustainable environment for the future, given uncertain climate changes and demands from farming restrictions.

My Research• The long term goal is to provide a guidance tool for farmers/ the

agricultural industry as to how and when to fertilise crops.

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Why is Phosphate Important?

• The model enables analysis of different P fertiliser strategies on grain yield, for different environmental conditions

Group Model Overview

Model Overview

After P is applied, the model

1.Tracks the movement of P and water through the soil

2.Includes the binding reactions of P to soil particles

3.Calculates the depth-dependent uptake of water and P into a developing root system

Model Overview• Our model is based on the one for nutrient and water uptake by

plant roots from unsaturated soil (Roose and Fowler, 2004). We estimate the phosphate and water concentration levels within the soil down to a depth of 2m.

• We set soil parameters such as water permeability and buffer power, for known characteristics of the soil measured by Bangor University.

• Climate conditions are taken from weather station data and root structures are known from pot experiments.

• The model inputs include; initial water and P concentrations in the soil, climate data and the fertiliser and soil cultivation strategy.

Scenarios to Consider

Cultivation Fertiliser Climate

A very wet climate

Site specific climateBanded 5cmBroadcastedPlough at 25, 20 or 10 cm Inverted plough

Min till gradient No cultivation No fertiliser

Problem Definition

Q1. What is the optimal fertiliser and soil management strategy for maximising plant P

uptake?

Q2. Does this strategy change for different climate conditions?

0 20 40 60 80 100 1200

20

40

60

80

100

120

140

160

180

Index 5Index 3Index 2

Soil depth (cm)

P am

ount

in s

oil (

mg/

kg)

Experimental Data

• P profile for an Olsen index 2, 3 and 5 soil.

Experimental Data• Field Trial set up:

– Initial P level is 9-10 mg P/l (P1)– Winter Barley measured at GS39 (19th May)– Varying fertilise amounts of Trisodium Phosphate (TSP) via

incorporation or placing

0 15 30 60 90 120 15 30 00

2

4

6

8

10

12

14

Experimental data at GS39

TSP applied (kg/ha P)

P up

take

(kg/

ha P

) at G

S 39

Incorporated Placed

Model Validation

• If we assume P index 2 (20 mg P/l) with exponential decay, similar results are obtained

• Total available P is only increased by 7%

Incorporated Placed

0 15 30 60 90 120 15 300

2

4

6

8

10

12

14

Experimental data10 mg P/l constant20 mg P/l decay

TSP applied (kg P/ha)

P up

take

at G

S 39

(kg

P/ha

)

0 10 20 30 40 50 60 70 80 90 10005

10152025

20 mg P/l decay 10 mg P/l constant

Depth (cm)P am

ount

in s

oil (

mg/

l)

Scenario Testing Results

• The best scenario for uptake is to mix the soil to a depth of 25 cm or Inverted plough.

• Placed fertiliser is better than incorporated by roughly 11%.

Site Specific Climate

mix 25 cm No cultivation mix 20 cm mix 10 cm Inverted plough

min till6.5

77.5

88.5

99.5

Incorporated (90 kg/ha P2O5) No fertiliser Placed (90 kg/ha P2O5)

Plough technique

P up

take

at G

S 92

(kg/

ha P

)

Scenario Testing Results

• The best scenario for uptake is to mix the soil to a depth of 25 cm or Inverted plough.

• Placed fertiliser is better than incorporated by roughly 11%.

• If the climate is particularly wet, average P uptake is increased by 2% across all scenarios, 6% for just incorporated.

A very wet climate

mix 25 cm No cultivation mix 20 cm mix 10 cm Inverted plough

min till6.5

77.5

88.5

99.5

Incorporated (90 kg/ha P2O5) No fertiliser Placed (90 kg/ha P2O5)

Plough technique

P up

take

at G

S92

(kg/

ha P

)

Effect of Buffer Power

• Results for an initial P index 1 soil (10mg/l P constant), 90 kg/ha P2O5 added to the top of the soil and then mixed down to 25 cm)

• The model is very sensitive to the buffer power.

• Therefore, to ensure accurate model predictions, a field-specific buffer power is required.

20 23.28 30 400

2

4

6

8

10

12

14

Buffer power

P up

take

at

GS3

9 (k

g/ha

P)

Effect of Soil Water Content

• Results for an initial P index 1 soil (10mg/l P constant), 90 kg/ha P2O5 added to the top of the soil and then mixed down to 25 cm.

• The model is less sensitive to the volumetric soil water content

• However to further improve the accuracy of the model, the volumetric soil water content profile in depth is required.

0.1 0.25 0.45 0.5510

10.2

10.4

10.6

10.8

11

11.2

11.4

Volumetric soil water content

P up

take

at

GS3

9 (k

g/ha

P)

1%

Root Model Conclusions

• Have incorporated temperature-dependent root growth which allows modelling of the winter period.

• The model outputs depend entirely on the model inputs

– buffer power– initial soil P and water profile to depth– site specific climate data

• Completed set of scenario testing

– best method is to invert plough and place fertiliser (banded)

• Different cultivation techniques and practices can lead to differences in soil P and water profiles

– To improve model prediction, more accurate site-specific data is needed

Thank you. Any Questions?