Irrigation Application Rate and Production under Centre- pivots Irrigation Application Rate and Production under Centre- pivots Ian McIndoe
Background Increasing use of centre-pivot irrigators for irrigating pasture Increasing length of centre-pivots ( m radius)
Xxx m pivot
Xxx m long pivot
General Pivot Operation Waters circular area Rotation speed typically 1-5 days Sprinklers m apart Increasing application rate with radius
The Problem Reduced application efficiency because of: Application rate often exceeding infiltration rate of soil Surface ponding Surface redistribution leading to drainage through soil profile Potential runoff Significant variability in soil and irrigation parameters
Why is it a Problem? Cost of applying extra water to compensate for dry areas Seasonal allocation limits constrain total seasonal use Leaching of nutrients (water quality implications) Wheel ruts and downtime due to pivots getting stuck Loss of production
Dilemma Short pivots cost significantly more per hectare irrigated than long pivots Long pivots can result in loss of production and lower application efficiency due to high application rates. Where is the tradeoff?
Previous work NZAEI research on irrigator application rate and uniformity –Focussed on what happens between the irrigator nozzles and ground level –Did not investigate what could happen in the soil –Did not include centre-pivots Bloomer research on quantifying surface redistribution (MAF SFF)
Alternative Approach Marshall English (Oregon State University): –Used an approach that combined climate, soil and irrigation parameters statistically to determine crop yield and irrigation efficiency Aqualinc adapted the English approach to: –Use historical daily climate data –Model typical NZ irrigation strategies –Expand the analysis to consider water use and production under centre-pivots
Irrigation and Soil Parameters Marshall English (Oregon State University): –Used an approach that combined climate, soil and irrigation parameters statistically to determine crop yield and irrigation efficiency Aqualinc adapted the English approach to: –Use historical daily climate data –Model typical NZ irrigation strategies –Expand the analysis to consider water use and production under centre-pivots
What Constrains Efficient Irrigation Unreliable water supplies Lack of supply or operational flexibility Unwanted stoppages Limited user training Poor design Limited or no system auditing Limited or no soil moisture measurement Limited or no use of irrigation performance measures
Factors Contributing to Improved Irrigation Efficiency Attitude – normal farm input, not just drought insurance Planned inputs delivering planned outputs Design of farm around irrigation system - layout Optimal use of labour, capital and energy Systems matched to range of soil and plant requirements – good design, on-demand supply Piped water schemes, use gravity as much as possible Measurements and monitoring for good operation Good maintenance Use of performance measures
Some things to look for General impression Operator experience and know how System flexibility – matched to crop/soil requirements Application uniformity and intensity Good maintenance Water and soil moisture measurement and use of information How rainfall is used – risk management Record keeping
Travelling gun, soft hose
Hard hose gun
Long lateral
Solid set
K Line
Fixed boom, soft hose
Rotary boom, soft hose
Centre-pivot
Spinner
Border-dyke