4    Results

4.1    OVERVIEW OF PROPERTIES

4.2    DAIRY FARMS

Information collected from the four dairy farms and the resulting indicator values are given in Table 4.2 to Table 4.5.

No financial values are recorded, as it was only possible to calculate a net profit after tax for properties 1A and 2A for the 1997 season. These were not directly comparable since property 1A was an owner operator farm and property 2A had a 50/50 share-milker and access was only available to the share-milker's accounts.

Data for farm 1A has been divided between the area irrigated with border strips and that with the big gun. On property 2B a split is shown between the first half of the season when the centre pivot was allowed one revolution in each cycle (25 mm applied) and the second half of the season when the pivot was allowed two revolutions in each cycle (50 mm applied).

Table 4.2 Data and Indicators for Farm 1A

Farm Code	1A
Effective Area (ha)	165
Year	96/97		97/98
Milk Solids (kg MS)	110,000		113,000†
Production/area (kg MS/ha)	670 (880)‡		680 (904)‡
Irrigation System	Border Strip	Big Gun	Border Strip	Big Gun
Mean depth applied (mm)	65	50	65	50
Number of irrigations	15	17	21	17
Total depth applied (mm)	970	850	1212	850
Irrigated Area (ha)	125	40	125	40
Total water applied (sub total) (m3 ´ 106)	1.2	0.3	1.7	0.3
Total water applied (m3 ´ 106)	1.6		2.0
Production/water use (kg MS/m3)	0.07		0.06
Water use/production (m3/kg MS)	15		18
Annual Energy Use (MWh)		280		280
Energy Input (subtotal) (kWh/m3)	0	0.82	0	0.82
Total Energy Input (kWh/m3)	0.18		0.14
Labour requirement (sub-total) (hours/season)	210	210	290	210
Total labour requirement (hours/season)	420		500
Labour requirement (subtotal) (hours/ha)	1.7	5.3	2.3	5.3
Total labour requirement (hours/ha)	2.5 §		3.0§
Ratio D/ET (mm/mm)	1.3	1.1	1.3	0.9
Ratio D/ET* (mm/mm)	2.3	2.0	1.6	1.1
Max. daily water abstraction rate (m3/day)	15,920		15,920
Nitrogen (kg/ha)	125		141
Phosphorous (kg/ha)	40		55
Potassium (kg/ha)	50		65
Sulphur (kg/ha)	28		40
Agri-chemical Use (l /ha)	5		5
Water Holding Capacity (mm)	Not measured
Soil Aggregate Stability (mm)	-		2.24
Soil pH	-		5.8
Soil Total Organic Carbon (%)	-		3.23
Soil Total Nitrogen (%)	-		0.31

† Estimated to end of season

‡ Higher figure calculated on effective area of 125 ha (see text)

§ Area weighted average (see text)

Table 4.3 Data and Indicators for Farm 1B

Farm Code	1B
Effective Area (ha)	192
Year	97/98
Milk Solids (kg MS)	120,000
Production/area (kg MS/ha)	630
Irrigation System	Border Strip
Mean depth applied (mm)	100
Number of irrigations	19
Total depth applied (mm)	1875
Irrigated Area (ha)	192
Total water applied (sub total) (m3 ´ 106)	3.6
Total water applied (m3 ´ 106)	3.6
Production/water use (kg MS/m3)	0.03
Water use/production (m3/kg MS)	30
Annual Energy Use (MWh)	0
Energy Input (subtotal) (kWh/m3)	0
Total Energy Input (kWh/m3)	0.00
Labour requirement (sub-total) (hours/season)	70
Total labour requirement (hours/season)	70
Labour requirement (subtotal) (hours/ha)	0.4
Total labour requirement (hours/ha)	0.4
Ratio D/ET (mm/mm)	2.0
Ratio D/ET* (mm/mm)	2.4
Max. daily water abstraction rate (m3/day)	17,000
Nitrogen (kg/ha)	150
Phosphorous (kg/ha)	40
Potassium (kg/ha)	0
Sulphur (kg/ha)	76
Agri-chemical Use (l /ha)	3
Water Holding Capacity (mm)	Not measured
Soil Aggregate Stability (mm)	2.21
Soil pH	6.3
Soil Total Organic Carbon (%)	3.18
Soil Total Nitrogen (%)	0.28

† Estimated to end of season

Table 4.4 Data and Indicators for Farm 2A

Farm Code	2A
Effective Area (ha)	265
Year	96/97	97/98
Milk Solids (kg MS)	316,000	355,000†
Production/area (kg MS/ha)	1190	1340
Irrigation System	Rotorainers
Mean depth applied (mm)	55	55
Number of irrigations	15	17
Total depth applied (mm)	830	943
Irrigated Area (ha)	265	265
Total water applied (sub total) (m3 ´ 106)	2.2	2.5
Total water applied (m3 ´ 106)	2.2	2.5
Production/water use (kg MS/m3)	0.14	0.14
Water use/production (m3/kg MS)	7	7
Annual Energy Use (MWh)	890	1110
Energy Input (subtotal) (kWh/m3)	0.40	0.45
Total Energy Input (kWh/m3)	0.40	0.45
Labour requirement (sub-total) (hours/season)	700	790
Total labour requirement (hours/season)	700	790
Labour requirement (subtotal) (hours/ha)	2.6	3.0
Total labour requirement (hours/ha)	2.6	3.0
Ratio D/ET (mm/mm)	1.1	1.0
Ratio D/ET* (mm/mm)	2.0	1.2
Max. daily water abstraction rate (m3/day)	12,100	12,100
Nitrogen (kg/ha)	147	150
Phosphorous (kg/ha)	65	56
Potassium (kg/ha)	30	30
Sulphur (kg/ha)	40	40
Agri-chemical Use (l /ha)	17	16
Water Holding Capacity (mm)	50 to 75
Soil Aggregate Stability (mm)	-	2.05
Soil pH	-	5.8
Soil Total Organic Carbon (%)	-	3.55
Soil Total Nitrogen (%)	-	0.34

† Estimated to end of season

Table 4.5 Data and Indicators for Farm 2B

Farm Code	2B
Effective Area (ha)	120
Year	97/98
Milk Solids (kg MS)	100,000†
Production/area (kg MS/ha)	830
Irrigation System§	Centre Pivot
Mean depth applied (mm)	25	50
Number of irrigations	15	10
Total depth applied (mm)	917
Irrigated Area (ha)	120	120
Total water applied (sub total) (m3 ´ 106)	0.5	0.6
Total water applied (m3 ´ 106)	1.1
Production/water use (kg MS/m3)	0.09
Water use/production (m3/kg MS)	11
Annual Energy Use (MWh)	260
Energy Input (subtotal) (kWh/m3)	0.24
Total Energy Input (kWh/m3)	0.24
Labour requirement (sub-total) (hours/season)	90	60
Total labour requirement (hours/season)	150
Labour requirement (subtotal) (hours/ha)	0.8 (1.8) ‡	0.5 (0.9)§
Total labour requirement (hours/ha)	1.3
Ratio D/ET (mm/mm)	1.0
Ratio D/ET* (mm/mm)	1.2
Max. daily water abstraction rate (m3/day)	5,000
Nitrogen (kg/ha)	155
Phosphorous (kg/ha)	30
Potassium (kg/ha)	15
Sulphur (kg/ha)	33
Agri-chemical Use (l /ha)	9
Water Holding Capacity (mm)	35 to 70
Soil Aggregate Stability (mm)	1.94
Soil pH	6.1
Soil Total Organic Carbon (%)	3.67
Soil Total Nitrogen (%)	0.32

† Estimated to end of season

‡ Requirement for whole season if shifted every day (see text)

§ Requirement for whole season if shifted every second day (see text)

4.2.1    Production Indicators

In line with industry convention, the unit of production for seasonal supply dairy farms has been taken as milk solids. For comparison, one kilogram of milk solids corresponds to approximately 11.8 litres of milk.

There were significant differences in milk solids production between the four farms. The ‘average’ performance figure used in the MAF farm monitoring model for Canterbury is 835 kg MS/ha for the 1996/97 season and projected to be 895 kg MS/ha for the 1997/98 season. Farm 2A was converted in 1995 and is now one of the highest performing farms in the district. Farms 1B and 2B are first year conversions, which partially explains their lower performance at 630 and 830 kg MS/ha.

Calculation of milk solids production per hectare for farm 1A has been calculated two ways to reflect current development on the property. The 40 ha of land irrigated with the big gun are currently in the process of reclamation from riverbed. When this area is included the milk solids production is below average. However, when the effective milking area is taken to include only the developed border strip irrigated part of the farm the production is about average.

Milk solids production per unit of water applied varied between 0.03 kg MS/m³ on the new conversion farm 1B to 0.14 kg MS/m³ on the top farm 2A. This corresponds to a range of water use of 30 to 7 m³/kg MS.

4.2.2    Labour Indicators

Labour requirements to operate the systems also varied widely. The most efficient system from a labour point of view was the new wide border strip system at 0.4 hours/ha per season. The labour requirement with this system was minimal and involved opening sluice gates and setting time clocks for one hour a day 3½ days out of seven. Requirements for the older narrow border strip system on farm 1A were higher at 1.7 and 2.3 hours/ha in 1996/97 and 1997/98 respectively.

The greatest labour requirement was for the big gun irrigator on farm 1A at 5.3 hour/ha per season. The Rotorainer system on farm 2A required 2.6 hours/ha in 1996/97 and 3.0 hours/ha in 1997/98 due to the greater number of irrigation cycles. The centre pivot system was predicted to have required 1.8 hours/ha for the whole season when shifted from paddock to paddock on a six-day cycle and 0.9 hours/ha if shifted every second day on a twelve-day cycle. Overall the labour requirement worked out at 1.3 hours/ha as the system was run for 90 days on a six-day cycle (15 cycles) and 120 days on a twelve-day cycle (10 cycles).

4.2.3    Energy Indicator

Energy requirements to operate the irrigation systems varied widely. The border strip irrigation systems were assumed to require no energy to operate. The big gun required the most energy at 0.82 kWh per cubic meter of water pumped. Note that this is equivalent to 3.0 MJ/m³ or 0.078 l diesel/m³. The Briggs Rotorainers required 0.4 kWh/m³ in 1996/97 and 0.45 kWh/m³ in 1997/98. The centre pivot system was more efficient at 0.24 kWh/m³.

4.2.4    Water Use Indicators

For the spray irrigation systems the ratio of water applied (D) to potential evapotranspiration demand (ET) was within the range 0.9 to 1.1 suggesting that they are operated close to the design situation. On farms 1A and 2A the ratio (D/ET) was slightly lower in the drought season of 1997/98 than in the previous season suggesting that these systems may not have coped as well with demand during the drought.

For the surface irrigation systems the ratio D/ET was greater than unity suggesting that more water was applied than actually required. The results for farm 1B should be treated with caution, as it is not clear as to whether the design application rate of 100 mm per irrigation was actually achieved.

For all systems the ratio of water applied (D) to rainfall adjusted seasonal water demand (ET*) was greater than one. This, combined with the ratio D/ET, suggests that the operation of these systems does not allow for utilisation of rainfall. This is most obvious for farms 1A and 2A for the 1996/97 season where water supply (D) closely matched evapotranspiration demand (ET) but was approximately double rainfall adjusted demand (ET*). For the spray irrigation systems between 20% and 100% extra water was applied than was actually necessary. Some of this would have been lost as windage with the remainder percolating below the root zone. On the surface irrigated farms, over irrigation of between 60% and 140% occurred, almost all of which would have been lost below the root zone.

Maximum daily abstraction rate was lowest on the farm with the centre pivot at about 5,000 m³/day or about 40 m³/ha-day. On the other spray irrigated farm this was estimated to be about 12,100 m³/day or 45 m³/ha-day. Maximum day water abstractions for the border strip irrigated farms were significantly higher. On farm 1A this was estimated to be 16,000 m³/day or about 100 m³/ha-day and on farm 1B 17,000 m³/day or 90 m³/ha-day.

4.2.5    Fertiliser and Agri-chemical Use Indicators

Fertiliser application rates were similar across all the farms in the trial. Potassium application on 1A was higher than the norm due to the use of a large quantity of chicken-litter on the 40 ha of developed riverbed. Sulphur application was higher that the norm on 1B reflecting capital fertiliser needs on this first year conversion.

Agri-chemical use is generally fairly low except on 2A which uses relatively high quantities of anti-bloat agents and cleaning chemicals reflecting the higher stocking density on this farm compared to the others.

4.2.6    Soil Indicators

Mean soil aggregate stability on all four dairy farms was above the critical limit of mean weighted diameter (MWD) of 1.5 mm suggested by Crop & Food. Variation between paddocks within the same farm was found to be greater than that between farms (See Appendix 1). The lowest value recorded was 1.77 mm on farm 2B and the highest 2.52 mm on farm 1A.

Average soil pH varied between 5.8 and 6.3. As with soil aggregate stability variation between paddocks on the same farm appear to be greater than the variation between farms.

Mean soil total organic carbon levels varied between 3.2% and 3.7% and were all above the 2% level, which is considered to indicate degraded soils. Intra farm variability was also greater than inter farm variability.

Mean soil total nitrogen levels varied between 0.28% and 0.34%. As with other soil factors, intra farm variability was greater than inter farm variability.

Water holding capacities for farms 2A and 2B were determined from comparison of neutron probe and quick draw tensiometer readings. This analysis showed that the quick draw tensiometer used during the trials was not correctly calibrated. Therefore the readings given should be regarded as indicative only. Insufficient data was available for properties 1A and 1B although the water holding capacity was expected to be less than those of 2A and 2B.

4.3    ARABLE FARMS

Information collected from the two arable farms and calculated indicators are summarised in Table 4.6 and Table 4.7.

The main point to emerge was the high degree of variability in this limited data. Yields, per unit area and per unit of water applied, were highly variable depending on farm, season, and variety. Similarly, the gross margins, per unit area and per unit of water consumption, were also highly variable. The most interesting comparisons can be made between different crops on the same farm.

On farm 3A the highest returning crops per unit of area were radish seed (97/98), ryegrass seed (both years), and wheat (Torfida 96/97) while poorest returns were gained from clover seed and Monad wheat (both 97/98). The highest returns per cubic meter of water were radish seed (97/98), wheat (Domino 96/97) and peas (97/98), while the poorest were from clover seed and Monad wheat (both 97/98).

On farm 3B the highest gross margin per hectare and per unit of water were obtained from seed potatoes (both years) and the poorest from clover seed (97/98).

One interesting comparison can be made between farms for production of ryegrass seed. On farm 3A ryegrass seed had the highest water use, with total depths of application of 175 mm. Yields of 2 tonne per hectare resulted in gross margins of over $2000/ha or about $1.20 per cubic meter of water. On farm 3B water application to ryegrass was lower at 80 to 120 mm. Yields of 1.1 to 1.3 tonnes per hectare resulted in gross margins below $1000/ha or between $0.80 and $1.20 per cubic meter of water. Fertiliser use for ryegrass seed production was also roughly double on farm 3A compared to farm 3B. Thus, although the return per hectare from ryegrass on farm 3A was more than double that on farm 3B the gross margin per unit of water applied was about the same.

Emerging from this information are some broad priorities for irrigation in situations where water is limited by resource or system constraints. For farm 3A best overall economic results are likely to be gained when priority is given to peas, very high value small seeds (radish), and barley. Wheat and ryegrass seed possibly form a medium priority group with clover seed a low priority. A similar pattern emerges for farm 3B with a high priority group including potatoes and barley, a medium priority group of peas, wheat, and ryegrass seed, and a low priority for clover seed. Since water input is only one factor of several that determine final yield and economic return it is not possible to draw definite conclusions from this limited data.

Table 4.6 Data and Indicators for Arable Farm 3A

Crop	Barley Feed	Wheat Domino	Wheat Torfida	Wheat Monad	Ryegrass Concord	Ryegrass Yatsyn	Clover Kopu	Radish	Peas Garden	Peas Garden
Year	96/97	96/97	96/97	97/98	96/97	97/98	97/98	97/98	96/97	97/98
Paddock	19	2	21	23	22	2	19	21	23	22
Area (ha)	13	8	4	10.5	10.5	8	13	4	10.5	10.5
Yield (t)	91	60	42	55	21.1	16	3.5	1.6	50.4	39.9
Mean depth water applied (mm)	35	35	35	35	35	35	35	35	35	35
Number of irrigations	2	2	4	2	5	5	4	4	3	2
Total depth water applied (mm)	70	70	140	70	175	175	140	140	105	70
Total water applied (m3 x 103)	9.1	5.6	5.6	7.4	18.4	14.0	18.2	5.6	11.0	7.4
Yield per unit area(t/ha)	7.0	7.5	10.5	5.2	2.0	2.0	0.3	0.4	4.8	3.8
Yield per unit water (kg/m3)	10.0	10.7	7.5	7.5	1.1	1.1	0.2	0.3	4.6	5.4
Gross Margin ($/ha)	1195	1551	1979	615	2100	2128	690	3240	1731	1342
Gross Margin per unit water ($/m3)	1.7	2.2	1.4	0.9	1.2	1.2	0.5	2.3	1.6	1.9
Nitrogen (kg/ha)	50	165	200	209	220	200	23	200	45	45
Phosphorous (kg/ha)	25	25	25	30	25	25	0	60	30	30
Potassium (kg/ha)	0	0	0	0	0	0	0	38	45	45
Sulphur (kg/ha)	30	30	33	36	30	30	0	62	36	36
Soil Aggregate Stability (MWD mm)	-	-	-	1.41	-	1.17	1.41	0.94	-	1.44
Soil pH	-	-	-	6.2	-	6.0	6.4	5.9	-	6.3
Soil Total Organic Carbon (%)	-	-	-	3.52	-	2.57	2.90	2.91	-	2.55
Soil Nitrogen (%)	-	-	-	0.32	-	0.25	0.28	0.28	-	0.25

Table 4.7 Data and Indicators for Arable Farm 3B

Crop	Barley Feed	Wheat Biscuit	Ryegrass Nui	Ryegrass Nui	Ryegrass Nui	Clover Aberherald	Peas Freezer	Peas Freezer	Potatoes Seed	Potatoes Seed
Year	96/97	97/98	96/97	96/97	97/98	97/98	96/97	97/98	96/97	97/98
Paddock	A	C	E	F	J	E	J	F	C	A
Area (ha)	16.5	8.5	6	4	13.4	6	13.4	4	8.5	16.5
Yield (t)	101	62.1	6.7	4.5	16.9	1.8	108	23.2	425	759
Mean depth water applied (mm)	40	40	40	40	40	40	40	40	40	40
Number of irrigations	2	3	2	2	3	3	2	3	6	6
Total depth water applied (mm)	80	120	80	80	120	120	80	120	240	240
Total water applied (m3 x 103)	13.2	10.2	4.8	3.2	16.1	7.2	10.7	4.8	20.4	39.6
Yield per unit area(t/ha)	6.1	7.3	1.1	1.1	1.3	0.3	8.1	5.8	50.0	46.0
Yield per unit water (kg/m3)	7.7	6.1	1.4	1.4	1.1	0.3	10.1	4.8	20.8	19.2
Gross Margin ($/ha)	1515	1153	833	948	975	688	1276	1032	9330	7757
Gross Margin per unit water ($/m3)	1.9	1.0	1.0	1.2	0.8	0.6	1.6	0.9	3.9	3.2
Nitrogen (kg/ha)	98	122	94	94	112	0	12	12	205	205
Phosphorous (kg/ha)	20	15	10	10	20	12	22	22	86	86
Potassium (kg/ha)	0	0	0	0	0	30	22	22	225	225
Sulphur (kg/ha)	24	17	12	12	12	36	2	2	0	0
Soil Aggregate Stability (MWD mm)	-	1.09	-	-	1.37	1.48	-	1.41	-	0.74
Soil pH	-	6.2	-	-	6.4	5.7	-	5.9	-	5.8
Soil Total Organic Carbon (%)	-	2.71	-	-	2.27	2.58	-	2.69	-	2.23
Soil Nitrogen (%)	-	0.24	-	-	0.21	0.24	-	0.25	-	0.20

Soil aggregate stability was below critical levels (1.5 mm MWD) in all paddocks sampled suggesting that these soils are degraded. Levels of pH were similar to those found under pasture. Total organic carbon and total nitrogen were on average lower than those encountered under pasture. There was no significant difference between the mean aggregate stability and pH between the two farms but the total organic carbon and total nitrogen were significantly lower, at the 5% level, on property 3B compared to property 3A.

4.4    IRRIGATION AUDITS

Irrigation audits of properties 2A and 3A were carried out using the methodology outlined in section 3.3.

4.4.1    Property 2A

4.4.1.1 System Specifications

• Dairy Farm.
• Two bore water sources.

	Bore #1 (old)	Bore #2 (new)
Bore diameter	300 mm	300 mm
Bore depth	80 m	72 m
Pump depth	50 m	50 m
Average water level	13 m	11 m
Drawdown	23 m at 259 m3/hr	12 m at 405 m3/hr

• Multiple ringmains with 125 to 200 mm diameter class B PVC pipe and 6" and 8" Fibrolite class B pipe.
• Irrigators

3 x Briggs Rotorainers delivering 150 m³/hr at 28 m head (~280 kPa)
1 x Briggs Rotorainer delivering 129 m³/hr at 28 m head (~280 kPa)
1 x Traymark Rotary Boom delivering 82 m³/hr at 28 m head (~280 kPa)

4.4.1.2 Hydrological Design

• In the Canterbury region the peak pastoral water demand is 330 m³/ha/week.
• The irrigation system is assumed to cover 270 ha of pasture.
• The crop factor used for calculating water demand is 1.0.
• Total pastoral irrigation demand equals 12,750 m³/day.
• The predominant soil type is Templeton Silt Loam.
• The readily available water holding capacity of a Templeton Silt Loam with a pasture rooting depth of 0.3 - 0.75 m varies between 68 to 135 mm. A small patch of Lismore Stony Silt Loam has a slightly lower water holding capacity.
• Depletion of available soil moisture should not exceed 50%. This equates to an average depletion of 50 mm or a required rotation period of 10 days.

4.4.1.3 System Capacity

• The total irrigation system needs to be able to supply the crop demand plus an allowance for application inefficiencies. These may range from 60-90%, in high temperatures, low humidity conditions a figure of 75% can be used. The total system capacity required is 17,000 m³/day.
• Bore #1 has a maximum capacity of 420 m³/hr or 10,080 m³/day.
• Bore #1 has a submersible and booster pump, together they are operating at 259 m³/hr. The submersibles maximum efficiency is achieved at 300 m³/hr. The booster pumps maximum efficiency occurs at 195 m³/hr.
• Bore #2 has a maximum capacity of 940 m³/hr or 22,560 m³/day.
• Bore #2 uses a submersible pump that is operating at 405 m3/hr. However, maximum efficiency is achieved at 330 m³/hr.

4.4.1.4 Application Rate

• The Briggs Rotorainers have an average application rate varying between 16.4 mm/hr at 129 m³/hr and 19.1 mm/hr at 150 m³/hr. The application rate of the Traymark irrigator is expected to be similar. The New Zealand standard 5103:1973 recommends a maximum water application on silt loams of 10.2 mm/hr. The high application rate of the travelling irrigators may cause some surface ponding.
• The Rotorainers and Traymark are operating in a variety of combinations. These include:
• 1 Rotorainer (off bore #1, no booster pump)
• 2 to 4 Rotorainers
• Rotorainers plus the Traymark
• At maximum capacity the system is operating at 660 m³/hr or 15,840 m³/day, resulting in a shortfall of over 1,160 m³/day.

4.4.1.5 Uniformity of Water Application

• Pressure variation across the whole system should not exceed ±10%, which is approximately equal to ±5% of flow. The variation of flow is of primary importance, however variation is often expressed in terms of pressure because it is easier to measure.
• Large variations across a system make it extremely difficult to manage the irrigation correctly.
• Pressure variation is calculated as the difference between the minimum and maximum outlet pressures, expressed as a percentage of the nominal outlet pressure.
• When the system is operating at full capacity, there is a pressure variation of up to ±22%, although more commonly it is approximately ±15%. Both these figures however are outside of design limits.
• With all 5 irrigators operating low pressure occurs on the opposite side of the road from the main farm and in the northern corner. Observations indicated that the hydrants in the northern corner of the farm operated at even lower pressure than was calculated by IRRICAD^TM. This may be due to a suspected drop in the performance of bore #2’s pump or errors in the elevation data.
• At different times of the year a variety of irrigator combinations are used. When the Traymark is turned off and the 4 Briggs Rotorainers are operating the worst pressure variation tested was ±18% and the best was ±4%. All hydrants operated at or above the nominal outlet pressure.
• With three of the Rotorainers operating off the two bore pumps (no booster pump), pipe pressures are above their recommended maximum along with hydrant pressures being well above the nominal pressure. The bore #2 pump by itself is unable to supply sufficient water to the 3 irrigators.
• Operating a single Briggs Rotorainer off bore #1 without the booster pump results in both high pipe and hydrant pressures. The pressure at the top of the bore is approximately 75 m. The maximum allowable pressure in the down stream pipes is 60 m.

4.4.1.6 Conclusions

• The irrigators are able to meet the maximum daily pastoral demand for water if operated for 21.5 hours per day. However, when application inefficiencies are taken into account there is a short fall of about 1,200 m³/day. This is the equivalent of an additional large Briggs Rotorainer being operated for 20 hours per day.
• There is sufficient capacity in the two bores to meet peak demand.
• There is insufficient pumping capacity to meet peak demand.
• The combined booster and submersible pump at bore #1 is extremely inefficient. The submersible is operating at close to maximum efficiency, however the booster pump is operating at the extreme end of its pump curve. Overall efficiency for hydraulic power output to energy input is 28%. By comparison a single pump should achieve 70% efficiency, this represents a considerable waste of energy.
• Pressure variation across the system is frequently outside of design limits.
• Pipe velocities are extremely high when the system is operated with 5 irrigators at once. 19% (2.4 km) of the pipes have velocities greater than 1.5 m/s and 5.5% are greater than 2.0 m/s. Generally pipe velocities should be kept below 1.5 m/s in order to minimise the risk of water hammer (unlikely to occur in this particular system) and prevent excessive friction losses and hence higher pumping costs. These high velocities also help to explain the large pressure variations across the system.

4.4.1.7 Recommendations

• The booster pump needs replacing with a pump whose flow characteristic better match the Garvin submersible pump at bore #1.
• Investigation is needed into the possible causes of the northern corner hydrants operating at lower pressures than was predicted, possibly due to a fall in actual pump performance.

• Branch mainline with 125 to 200 mm diameter class B PVC pipes
• Four, 400 m siderolls with 33 Naan 5 mm nozzles delivering 52.8 m³/hr at 31.6 m (45 psi) per sideroll
• One, 265 m sideroll with 22 Naan 5 mm nozzles delivering 34.7 m³/hr at 31.6 m (45 psi)
• 10 to 18 sprinklers on 75 mm (3² ) aluminium hand shift pipes

• Due to the crop cycle and environmental conditions December is the month with the highest water demand. Average ET = 4.7mm/day (330 m³/ha/wk).
• In December up to 97 ha of crop demands irrigation. Forty-five hectares, in barley and wheat, are considered sacrifice crops if insufficient water is available. These two crops are also less likely to suffer water stress due to their deep root system, hence access to a greater volume of soil water.
• On a cropping farm the crop factor varies throughout the season from 0.1 to 1.0, depending on the physiological crop growth stage. In December the crop factor is between 0.7 and 0.8.
• With an ET of 4.7 mm/day and a crop factor of 0.75, plant water demand equals 247 m³/ha/wk.
• Available water holding capacity is dependent on the soil type and crop rooting depth. With a crop rooting depth of between 0.3 to 1.1 m on a Templeton Silt Loam the readily available water holding capacity varies between 68 and 188 mm.
• Depletion of available soil moisture should not exceed 50%.
• Total crop demand equals 3420 m³/day or 1835 m³/day if the barley and wheat are sacrificed.

• The system needs to have the capacity to meet the peak crop demand plus reasonable water loss due to application inefficiencies. A figure of 75% can be used.
• Depending on whether the sacrifice crops are being irrigated or not and taking into account system inefficiencies, a total system capacity of 2450 to 4560 m³/day is required.
• The well is currently at its maximum capacity. During periods of low static water levels, water is drawn down to within 2 to 3 m of the pump. In the past the pump has stopped due to a low water level cut out.
• The submersible pump is operating at 73% efficiency (147 m³/hr). Maximum efficiency of 79% is achieved at the higher pumping rate of 200 m³/hr.

• The application rate of 3.9 mm/hr from the siderolls is less than the recommended maximum of 10.2 mm/hr for a silt loam. Hence there is no problem with surface run-off or water lying on the surface.
• Each sideroll and handshift sprinkler line is operated for seven hours per shift. Two large siderolls and either the small sideroll or handshift sprinklers are operated at once. Three seven-hour rotations occur each day. This means that the system is operating at 147 m³/hr or 3087 m³/day.
• The ability to apply of 3087 m³/day is at the lower end of the total system requirement and is consistent with the farmer's practice of having to sacrifice part of the wheat and barley crop when there is insufficient water.

• Pressure variation across the whole system should not exceed ±10%, which is approximately equal to ±5% of flow.
• Pressure variation along the large sideroll is ±7.3% (±3.3% of flow) and ±4.3% for the small sideroll (±2.1% of flow).
• In the worst case situation where a large side roll is operating close by the pump and the other large side roll is at the highest elevation of the farm with the small sideroll in between total system pressure variation equals ±32% (±13% of flow).
• Balancing the system by creating pressure loss at the hydrant with the highest pressure could improve total system pressure variation to ±17% (±7% of flow).

• There is insufficient water available to meet the total demand.
• Large pressure variations exist across the irrigation system.

• Additional water can only be obtained by drilling a new bore. It is unlikely that the existing bore will yield a higher flow of water.

• The pressure variation across the system could be improved by increasing the pressure loss at high-pressure hydrants that are close to the bore. This can be achieved by throttling back the hydrant value. Further improvements could be made by reducing the nozzle size of each sprinkler on the large siderolls and hence the flow along each sideroll. This however would require operating 3 of the 4 large siderolls at once in order to achieve the same system capacity. This would also have a marked increase in the labour required.

Contact for Enquiries

MAF Information Services
Pastoral House
25 The Terrace
PO Box 2526
Wellington, NEW ZEALAND

Fax: +64 4 894 0721
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