Effects of variability in fertiliser application on hill country production economics

1. Effects of variability in fertiliser application on hill country production economics Allan Gillingham (Research Consultant) Alister Metherell

2. Hill pastures • All hill country is variable • This means differences in pasture growth potential • Often in complex patterns

3. “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

4. Factors affecting “lost” production • Fertiliser application rate factors • Land productivity, and initial nutrient status • Fertiliser residual properties

5. What causes variability in application rate • Swath shape • Discharge rate • Track spacing • Cross wind / altitude • Aircraft speed

6. Estimation of CV% • Usually use a single swath shape and overlap this at a range of track spacings

7. To date the accuracy of track spacing has depended on pilot skill and experience • Now GPS increasingly being used for guidance and job record

8. 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% ?

9. 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?

10. Effects of variations in aircraft altitude and speed, and in cross wind not included in this evaluation

11. 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)

12. 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

13. Selected swath shape • Cresco with superphosphate

14. Random variation • Added random variation in track spacing of up to 33 or 66% and variation in flow rate of 50%

15. Results: Fertiliser application rate and Soil Phosphate

16. Variation in fertiliser application rate with 66% variation in 12m track spacing

17. 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

18. Soil P test distribution with 66% variation from 12m track spacing

19. Results • Pasture dry matter production

20. Effect of variability in fertiliser application rate on pasture DM production Even Spread Mean ±1 S.D. 95% 5%

21. 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

22. 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

23. 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

24. Nitrogen • Straight line response • Little effect of variability in fertiliser rate on pasture response

25. Thank you