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Effects of variability in fertiliser application on hill country production economics - PowerPoint PPT Presentation


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Effects of variability in fertiliser application on hill country production economics. Allan Gillingham (Research Consultant) Alister Metherell . Hill pastures . All hill country is variable This means differences in pasture growth potential Often in complex patterns.

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slide1

Effects of variability in fertiliser application on hill country production economics

Allan Gillingham

(Research Consultant)

Alister Metherell

hill pastures
Hill pastures
  • All hill country is variable
  • This means differences in pasture growth potential
  • Often in complex patterns
slide3
“Lost” pasture production can occur in two ways:-
  • The same rate of fertiliser being applied to different production zones
  • Variation in fertiliser application rate within a zone
factors affecting lost production
Factors affecting “lost” production
  • Fertiliser application rate factors
  • Land productivity, and initial nutrient status
  • Fertiliser residual properties
what causes variability in application rate
What causes variability in application rate
  • Swath shape
  • Discharge rate
  • Track spacing
  • Cross wind / altitude
  • Aircraft speed
estimation of cv
Estimation of CV%
  • Usually use a single swath shape and overlap this at a range of track spacings
slide7
To date the accuracy of track spacing has depended on pilot skill and experience
  • Now GPS increasingly being used for guidance and job record
slide8
Results show that even with GPS track spacing CV% may be up to 33%.eg 15m ± 5m
  • Difficult to estimate without GPS

Assume CV = 66% ?

slide9
Variability in discharge along the flight path also varies
  • For superphosphate

– Helicopter CV % = 12-27

- Fixed wing CV % = 37-67

  • What effect does this have on spread CV% estimates?
slide10
Effects of variations in aircraft altitude and speed, and in cross wind not included in this evaluation
slide11
What are the effects of land productivity and initial nutrient (P) status?
  • eg “High” (stocking rate =20/ha; Olsen P =30)

“Medium” (SR = 19; P =15)

“Low” (SR = 4; P =8)

slide12
Probability of fertiliser application rate occurring on any one site estimated by @Risk analysis.
  • Effects of variability in fertiliser application rate on soil P and productivity assessed by OVERSEER analysis
selected swath shape
Selected swath shape
  • Cresco with superphosphate
random variation
Random variation
  • Added random variation in track spacing of up to 33 or 66% and variation in flow rate of 50%
results
Results:

Fertiliser application rate and

Soil Phosphate

variability of overall spread cv
Variability of overall spread(CV%)
  • 33% track error = 30
  • 33% track plus 50% flow error= 42
  • 66% track error = 48
  • 66%track plus 50% flow error = 58
results1
Results
  • Pasture dry matter production
effect of variability in fertiliser application rate on pasture dm production
Effect of variability in fertiliser application rate on pasture DM production

Even Spread

Mean

±1 S.D.

95%

5%

results2
Results
  • All scenarios showed less than 1% depression in long term (10 yr) mean pasture DM production due to variability in P fertiliser application rate
conclusions
Conclusions

Variability in fertiliser application rate has little effect on average pasture production because of-

  • Compensating random rate effects
  • High residual properties of P fertiliser
conclusions1
Conclusions
  • These results differ from situations where exactly the same pattern of P application occurs at every application
  • This is unlikely to occur in hill country
nitrogen
Nitrogen
  • Straight line response
  • Little effect of variability

in fertiliser rate

on pasture

response