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Monitoring yield, field quality and water use efficiency of irrigated summer forage crops (maize and turnips) on

commercial dairy farms’ Final report to DairyTas

July 2007

Richard Rawnsley and Danny Donaghy Tasmanian Institute of Agricultural Research

Mark Fergusson Tasmanian Department of Primary Industries and Water

1

Table of contents Executive summary...................................................................... 2

Project team .................................................................................................5

Acknowledgements...................................................................... 5

Background................................................................................... 6

Methods......................................................................................... 7

Location of sites ...........................................................................................7

Irrigation applications ...................................................................................8

Soil moisture and climate .............................................................................8

Crop development and yield assessment.....................................................8

Herbage quality ............................................................................................9

Results ........................................................................................ 10

Turnips: ......................................................................................................10

Yields and water use efficiency...............................................................10

Plant density and soil moisture ...............................................................11

Costs of production.................................................................................12

Feed quality ............................................................................................13

Maize..........................................................................................................16

Yields and water use efficiency...............................................................16

Plant density and crop health status .......................................................17

Growing degree days..............................................................................19

Costs of production.................................................................................22

Feed quality ............................................................................................24

Discussion .................................................................................. 25

References .................................................................................. 29

2

Executive summary This document is the final report to DairyTas. The research in this project was

successfully completed to the schedule detailed in the project proposal. The principal

objective of the project was to:

Monitor the on-farm yields, feed quality, water use efficiency and cost of production

of irrigated maize and turnips during the 2006-07 summer season on commercial

dairy farms.

This has been achieved through detailed motoring of four maize crops located at

Mella, Bushy Park, Flowerdale and Sassafras and four turnips crops located at Mella,

Bushy Park, Ridgley and Elliott. This monitoring included a minimum of four visits to

each site. Crop health and development, plant density, irrigation inputs, soil moisture

and climatic conditions were monitored. Crop production costs were determined

through communication with the growers and yield and feed quality were assessed at

crop maturity. A summary of the results is given in Tables 1 and 2.

A series of two field days were held on the 12th and 13th July 2007 at Scottsdale and

Smithton, respectively. Results of this study were communicated at these days. In

addition to these two field days, trial results were communicated to growers by the

participation of Richard Rawnsley and Mark Fergusson at maize field days organised

by seed companies held at Flowerdale and Sassafras in March and April 2007,

respectively. The outcomes of the study will be the topic for articles in the Australian

Dairy Farmer magazine and the Pasture Plu$ newsletter. The on-farm maize and

turnip information also formed part of a paper presented to the Grasslands Society

Conference by Richard Rawnsley. Since making the presentations to industry TIAR

has received on-going enquiries for information about maize and turnips. The study

provided TIAR staff with reliable information about forage crops to communicate to

dairy farmers.

3

Table 1 A summary of yield, water use efficiency, cost of production and feed quality of Turnips monitored on four commercial dairy farms.

Turnips

Mella Elliott Ridgley Bushy Park Average

Yield (t DM/ha) 8.2 11.0 8.2 8.0 8.85

Irrigation inputs (ML/ha) Nil 2.30 1.77 1.70 1.92

Rainfall (ML/ha) 1.51 0.83 1.06 0.56 0.99

Total water received (ML/ha) 1.51 3.13 2.83 2.26 2.43

WUE (t DM/ML) 5.43 3.51 2.90 3.54 3.85

Cost ($/ha)

Ground preparation and sowing 497 350 300 180 332 Fertiliser 347 190 75 130 186 Pesticides 129 40 20 63 Irrigation 140 120 120 127 Additional costs 22 22 Total costs of production ($/ha) 995 720 515 430 729 Costs of production (cents/kg DM) 12.1 6.5 6.3 5.4 7.6 Feed Quality

Dry Matter (%) 8.6 9.1 9.0 10.0 9.2 ME (MJ/kg DM) 12.6 13.3 13.0 14.1 13.3 DMD (%) 86.1 90.2 88.1 94.6 89.8 CP (%) 15.5 17.2 18.0 15.4 16.5 NDF (%) 26.1 27.3 25.4 23.4 25.6 ADF (%) 20.8 19.2 19.2 19.8 19.8

4

Table 2 A summary of yield, water use efficiency, cost of production and feed quality of Maize monitored on four commercial dairy farms.

Maize

Mella Sassafras Flowerdale Bushy Park Average

Yield (t DM/ha) 15.8 12.8 23.1 12.5 16.1

Irrigation inputs (ML/ha) Nil 1.02 4.31 5.00 3.44

Rainfall (ML/ha) 1.80 1.32 1.35 1.68 1.54

Total water received (ML/ha) 1.80 2.34 5.77 6.68 4.15

WUE (t DM/ML) 8.78 5.47 4.00 1.87 5.03

Cost ($/ha)

Ground preparation and sowing 1081 505 720 680 747

Fertiliser 736 471 775 640 656

Pesticides 43 259 397 130 207

Irrigation 60 259 300 206

Harvesting 883 665 1336 650 884

Additional costs 109 109

Total costs of production ($/ha) 2853 1960 3487 2400 2675

Costs of production (cents/kg DM) 18.0 15.3 15.1 19.2 16.9

Feed Quality

Dry Matter (%) 33.4 30.0 29.2 26.3 29.7 ME (MJ/kg DM) 10.6 9.7 9.2 10.1 9.9 DMD (%) 74.3 69.1 66.1 71.1 70.2 CP (%) 7.1 7.6 6.2 8.7 7.4 NDF (%) 41.9 50.7 50.5 46.5 47.4 ADF (%) 22.6 26.2 30.6 25.7 26.3

5

It was concluded that maize and turnips do not appear to be cost effective if grown to

replace productive pasture on the dairy farm. If however, these paddocks are poor

producing and require renovation, both maize and turnips are economically viable

options to include as part of this renovation. In addition, if water is a limiting resource

on the farm and some of the irrigated pasture paddocks are likely to be unproductive,

both maize and turnips will provide significantly more feed per unit of water than

these pastures. The results demonstrated in this study have shown that both turnips

and/or maize can be successfully grown as a forage crop by dairy farmers aiming to

increase their farm profitability and can be used as a means of improving the

robustness of their farming system by reducing the reliance on brought in feed and

making better use of available water resources.

Project team

The current project was managed by Richard Rawnsley and Mark Fergusson with

technical support provided by Scott Carlson and Peter Chamberlain. Dr. Danny

Donaghy provided management support for this project. Lesley Irvine provided

assistance with farmer details and collection of cost production figures.

Acknowledgements We would like to thank the DairyTas Board for supporting this project and the dairy

farmers involved for their significant contribution to this project. In addition, we would

like to thank harvesting contractors Michael McNamara and Andrew Wylie and seed

representatives Alex Ford from Pioneer Seeds and Dean Fry from Snowy River

Seeds for their support of the project.

6

Background TIAR have monitored the production of pasture and forage crops under irrigation at

the Elliott Research and Demonstration Station (ERDS) over the last three summer

seasons and found that maize and turnips have higher production and water use

efficiency than other crops and grasses (Rawnsley et al. 2006). Improvements in

the amount of forage grown and consumed on-farm are critical for further

productivity gains in the dairy industry. TIAR research has identified that turnips

and maize are both high performance irrigated crops when grown under research

conditions but there is little information regarding their yields, feed quality, water

use efficiency and cost of production, particularly maize, on commercial farms in

Tasmania.

Maize is the most widely grown fodder crop in the world and is one of the highest

yielding forage crops. Growing maize in a dairy feedbase system is not a new idea

and according to Moran (1996), in 1912, a dairy text book reported that maize was

one of the easiest fodder crops to grow and recommended it be grown and used as a

supplement for grazing dairy cows in later summer/early autumn. According to Moran

(1996) the adoption of maize technology is Australia has been very slow and is most

likely a result of the traditional emphasis on low-cost pasture based grazing systems.

The use of sub-tropical forages in a temperate environment is often restricted by cool

growing temperatures, however maize is much more cold tolerant than many other

tropical forages and the majority of maize is grown in temperate regions of the world.

The growing of brassica crops in spring and summer is a common way to fill the

summer feedgap on farms in southern temperate areas of Australia. It is estimated

that brassica crops are grown on approximately 70% of dryland dairy farms in

southern Victoria and Tasmania, with turnips being the most popular crop. Turnips

are reported to be the best value for money in situations when forage is required in

late January (Eckard et al. 2001), and have been shown to have double the water

use efficiency of pastures (Rawnsley et al., 2006).

This project aimed to monitor the forage production, water use efficiency, and cost of

production of maize and turnips on commercial farms and provide information to the

dairy industry about the potential of these crops to increase on-farm productivity.

7

Methods

Location of sites

Seven dairy farms located across Tasmania took part in this study (Plate 1). Sites

were established on commercial dairy farms at Mella, Flowerdale, Elliott, Ridgley,

Sassafras and Bushy Park. Apart from the maize and turnips grown at Mella all sites

were irrigated. At Bushy Park both maize and turnips were monitored under irrigation

with a centre pivot and a travelling gun, respectively. At Flowerdale and Sassafras

maize was monitored with both crops being irrigated with a travelling gun. At Ridgley

and Elliott turnips were monitored with both crops also being irrigated with a travelling

gun (Table 3).

Table 3 Field site locations, irrigation set-up and crop grown. Site number Location Irrigation Crop

1 Mella Nil Turnips and Maize

2 Flowerdale Travelling gun Maize

3 Elliott Travelling gun Turnips

4 Ridgley Travelling gun Turnips

5 Sassafras Travelling gun Maize

6a Bushy Park Travelling gun Turnips

6b Bushy Park Centre-Pivot Maize

Plate 1 Location of field sites across Tasmania.

8

Irrigation applications

Flow meters were installed to monitor the quantity of water applied at sites 3, 4, 5

and 6a. At site 2, a permanent flow meter to the irrigation pump was already

installed. At site 6b, no irrigation monitoring was installed due to the high price

associated with installing a flow meter on a centre pivot irrigator. At site 6b, the

quantity of irrigation water applied was calculated by recording the average amount

of water applied per hour and the number of hours of operation. Rainfall received at

each site was collated from the SILO weather database

(http://www.bom.gov.au/silo/).

Soil moisture and climate

Hansen data loggers were installed at each site. Loggers recorded soil temperature

(°C) at a depth of 10 cm and moisture levels in centibars (cb) at depths of 15, 30 and

45cm at each site. Weather stations were installed at site 1 and 6b. These stations

monitored air and soil temperature, dew point, relative humidity and solar radiation.

Crop development and yield assessment

All sites were visited regularly and a crop assessment undertaken. Growth stage of

the crop, crop health, soil moisture, and level of pest, weed and disease infestation

were visually assessed. Plant density was assessed using a 1m2 quadrat for turnips

and the number of plants per 10m length for maize. This was repeated 10 times in

random positions throughout the site. In the week prior to grazing of the turnips and

harvesting of the maize a yield assessment of the crops was undertaken. For the

turnips this involved assessing the fresh yield of the turnips within a 1 m2 quadrat.

This was repeated four times at random positions throughout the site. A sub-sample

of turnips was selected at random and taken from the field back to the laboratory

were the turnips were separated into leaf and bulb. The fresh weight of the sub-

samples were recorded and the sub-samples placed in forced draught oven at 700C

for 48hr. The sub-sample dry weight was recorded and the DM % of the turnips bulbs

and tops calculated. For the maize crops, yields were assessed by randomly

selecting a 10m length in a row and counting the number of plants in that length.

Every 5th plant in the 10m length was cut to a height of 5cm and bundled together to

form a sample. The bundle was weighed and the number of plants counted and

average plant fresh weight calculated. This was repeated six times. Two plants from

9

each bundle were removed and combined to form a sub-sample. This sub-sample

was chopped and uniformly mixed. A sub-sample of the ground material was taken,

weighed and dried at 700C for 48hr in a forced draught oven. The DM% was

calculated and the dry weight per plant calculated. This was then multiplied by the

plant density to give the yield per hectare. In addition, a second sub-sample was

taken in which the maize crop was divided into stover (stems, leaves, and husks) and

ear (cob and grain) components and the proportion of stover and ear calculated.

Yields were compared to those assessed by the harvesting contractors.

Herbage quality

The dried herbage samples from each site were ground to pass through a 1.0mm

sieve. Herbage samples were analysed by FEEDTEST, Department of Primary

Industries, Hamilton for crude protein (CP; nitrogen x 6.25), neutral detergent fibre

(NDF) and dry matter digestibility (DMD). Values were estimated using near infrared

spectroscopy (NIRS). Near infrared spectra were collected on all samples using a

Foss-NIR Systems 5000 scanning monochromator in conjunction with Infrasoft

International software. Near infrared spectroscopy calibrations for CP, NDF, ADF and

estimated in vivo DMD had previously been derived on large sample populations

using the procedures of Shenk and Westerhaus (1991).

Reference methods used for NIRS calibrations were as follows: CP using the

Kjeldahl method, NDF and ADF by the method of van Soest and Wine (1967) but

using ANKOM® equipment and DMD using a pepsin-cellulase technique based on

that of Clarke et al. (1982), with analytical values adjusted using a linear regression

based on similar samples of known in vivo DMD. Any spectral outliers from the

calibrations were analysed by wet chemistry techniques as described above.

Metabolisable energy (ME; MJ/kg DM) values were estimated from predicted DMD.

ME = (0.17 x DMD) - 2 (Standing Committee on Agriculture 1990).

10

Results The following is summary of the results taken from each of the field sites.

Turnips:

Yields and water use efficiency

The yield of turnips varied between 8.0 and 11.0 t DM/ha betweens sites, with an

average yield of 8.8t DM/ha (Table 4). The mean amount of irrigation applied at the

three irrigated sites was 1.92 ML/ha, while the average water use efficiency was

3.85t DM/ML of water received. The average proportion of tops (leaf material) to bulb

was 53% tops and 47% bulb. This varied between sites with more bulb material

produced than top material at Mella, while more top than bulb material was produced

at the remaining three sites. The lower proportion of top material at Mella was a

result of a high percentage of leaf loss due to diamondback moth (Plate 2).

Plate 2 Turnips grown at Mella displaying leaf loss due to diamondback moth.

11

Table 4 A summary of yield and water use efficiency of Turnips monitored on four commercial dairy farms.

Turnips


Yield (t DM/ha) 8.2 11.0 8.2 8.0 8.8

DM proportion tops 0.40 0.59 0.53 0.60 0.53

DM proportion bulb 0.60 0.41 0.47 0.40 0.47

Irrigation inputs

(ML/ha) Nil 2.30 1.77 1.70 1.92

Rainfall (ML/ha) 1.51 0.83 1.06 0.56 0.99

Total water received

(ML/ha) 1.51 3.13 2.83 2.26 2.43

WUE (t DM/ML) 5.43 3.51 2.90 3.54 3.85

Plant density and soil moisture

Turnip plant densities varied between sites with the highest density occurring at

Elliott were the plant density was 40 plants/m2. The lowest density occurred at

Ridgley were the plant density was 20 plants/m2. At Mella, Elliott and Bushy Park

there was considerable variation in the plant density across the site. The plant

population at Ridgley was much more uniform then all other sites.

0

5

10

15

20

25

30

35

40

45

50

Mella Elliott Ridgley Bushy Park

Pla

nt d

ensi

ty (p

lant

/m2)

.

Figure 1 Mean turnip density (plants/m2) at four commercial dairy farms. Standard error of means shown as error bars.

12

Available soil moisture varied between sites. Ridgley had the highest amount of

available soil moisture with only some moisture stress being observed towards the

end of plant maturity. Three distinct irrigation events are clearly displayed in the soil

moisture curve for Elliott, while moisture was a major limiting factor to the growth of

turnips at Bushy Park where the soil moisture was constantly greater than 200 cb.

The dryland turnips crop at Mella had sufficient available soil moisture to support

crop growth between November and the middle of December, after which the soil

moisture became limiting.

Figure 2 The soil water potential of turnips crop grown at Bushy Park (a), Ridgley (b), Mella (c) and Elliott (d) at a depth of 15cm (-), 30cm (-) and 45cm (-).

Costs of production

The average costs of production of turnips was 7.6 c/kg DM or $729/ha (Table 5).

Ground preparation and sowing were the most significant cost, ranging between

$180 and $500/ha. The average fertiliser cost was $186/ha, while irrigation and

pesticide application costs varied depending on location.

0

25

50

75

100

125

150

175

200

14-Feb-07 21-Feb-07 28-Feb-07 07-Mar-07 14-Mar-07 21-Mar-07 28-Mar-07 04-Apr-07 11-Apr-07 18-Apr-07 25-Apr-07

Soi

l wat

er p

oten

tial

0

25

50

75

100

125

150

175

200

27-Oct-06 10-Nov-06 24-Nov-06 08-Dec-06 22-Dec-06 05-Jan-07 19-Jan-07

Soi

l wat

er p

oten

tial

7

0

25

50

75

100

125

150

175

200

2-Feb-07 9-Feb-07 16-Feb-07 23-Feb-07 2-Mar-07 9-Mar-07 16-Mar-07 23-Mar-07

Soi

l wat

er p

oten

tial

7

0

25

50

75

100

125

150

175

200

22-Nov-06 29-Nov-06 06-Dec-06 13-Dec-06 20-Dec-06 27-Dec-06 03-Jan-07 10-Jan-07 17-Jan-07

Soi

l wat

er p

oten

tial

c

a b

d

13

Table 5 A summary of the cost of production of turnips monitored on four commercial dairy farms.

Turnips


Cost ($/ha)

Ground preparation

and sowing 497 350 300 180 332

Fertiliser 347 190 75 130 186 Pesticides 129 40 20 63 Irrigation 140 120 120 127 Any other costs 22 22 Total costs of

production ($/ha) 995 720 720 430 729

Costs of production

(cents/kg DM) 12.1 6.5 6.5 5.4 7.6

Feed quality

The DM% percentage of turnips varied between 8.6% at Mella and 10.0% at Bushy

Park (Table 6). The average ME was 13.2 MJ/kg DM with a range of 12.6 to 14.1

MJ/kg DM. The highest CP concentration was 18.0% for the turnips grown at

Ridgley. The lowest CP concentration occurred at Bushy Park, 15.4 %. The mean CP

concentration was 16.5%. The average NDF% and ADF% of the turnips was 25.6

and 19.8%, respectively.

Table 6 A summary of the herbage quality of turnips monitored on four commercial dairy farms.

Turnips


Feed Quality

Dry Matter (%) 8.6 9.1 9.0 10.0 9.2

1ME (MJ/kg DM) 12.6 13.3 13.0 14.1 13.3 DMD (%) 86.1 90.2 88.1 94.6 89.8

CP (%) 15.5 17.2 18.0 15.4 16.5

NDF (%) 26.1 27.3 25.4 23.4 25.6

ADF (%) 20.8 19.2 19.2 19.8 19.8

1. Metabolisable energy (ME) values estimated from predicted DM digestibility (SCA, 1990).

Both the bulbs and the tops were individually analysed for herbage quality. The CP

concentration was discernibly different between the tops and the bulbs at each of

14

sites with the tops have approximately 60% more CP than the bulb. On average the

CP% of the tops was 20.4% compared to 12.4% for the bulbs.

0

5

10

15

20

25

bulbs tops bulbs tops bulbs tops bulbs tops

BushyPark

BushyPark

Ridgley Ridgley Mella Mella Elliott Elliott

CP

(%)

Figure 3 The crude protein concentration (%) of both the top and bulb components of turnips grown on four commercial dairy farms.

The turnip bulbs were found to have a higher ME and DMD value than tops. The

average ME and DMD of the bulbs was 13.8 MJ/kg DM and 93.0%, respectively,

compared to 13.0 MJ/kg DM and 88.2%, respectively, for the tops.

10.5

11

11.5

12

12.5

13

13.5

14

14.5

15


BushyPark

BushyPark


ME

(MJ/

kg D

M)

Figure 4 The metabolisable energy content (MJ/kg DM) of both the top and bulb components of turnips grown on four commercial dairy farms.

15

75

80

85

90

95

100


Bushy Park Bushy Park Ridgley Ridgley Mella Mella Elliott Elliott

DMD

(%)

Figure 5 The dry matter digestibility (%) of both the top and bulb components of turnips grown on four commercial dairy farms.

The NDF% was found to be lower in the bulbs than in tops at all sites except Elliott.

The average NDF% of the bulbs and the tops was 23.6 and 27.8%, respectively.

0

5

10

15

20

25

30

35


Bushy Park Bushy Park Ridgley Ridgley Mella Mella Elliott Elliott

ND

F (%

)

Figure 6 The NDF (%) of both the top and bulb components of turnips grown on four commercial dairy farms.

There was little variation in the ADF% between the bulbs and the tops at Bushy Park,

Ridgley and Mella. At Elliott the ADF% of the bulbs was 21.4% compared to 17.6%

for the tops. The average of ADF% of the bulbs and tops across all sites was 20.5


16

0

5

10

15

20

25


BushyPark

BushyPark


AD

F (%

)

Figure 7 The ADF concentration (%) of both the top and bulb components of turnips grown on four commercial dairy farms.

Maize

Yields and water use efficiency.

The yield of maize varied between 12.5 and 23.1 t DM/ha betweens sites, with an

average yield of 16.1 t DM/ha (Table 7). The mean amount of irrigation applied at the

three irrigated sites was 3.44 ML/ha, while the average water use efficiency was 5.03

t DM/ML. The yield component of the maize was found to be very close to 50% ear

and 50% stover across all sites.

Table 7 A summary of yield and water use efficiency of Maize monitored on four commercial dairy farms.

Maize


Yield (t DM/ha) 15.8 12.8 23.1 12.5 16.1

Proportion Ear 0.52 0.49 0.57 0.47 0.51

Proportion Stover 0.48 0.51 0.43 0.53 0.49

Irrigation inputs

(ML/ha) Nil 1.02 4.31 5.00 3.44

Rainfall (ML/ha) 1.80 1.32 1.35 1.68 1.54

Total water received

(ML/ha) 1.80 2.34 5.77 6.68 4.15

WUE (t DM/ML) 8.78 5.47 4.00 1.87 5.03

17

Plant density and crop health status

The mean plant density of the maize crop was found to vary between 83,000

plants/ha at Mella to only 53,400 plants/ha at Bushy Park. All plants densities were

below the target density of 95,000 plants/ha. There was significant variation in plant

density at Bushy Park and this was due to a significant proportion of the area having

very low densities due to seedling losses.

0

10000

20000

30000

40000

50000

60000

70000

80000

90000

100000

Mella Sassafras Flowerdale Bushy Park

Den

sity

(pla

nts/

ha)

.

Figure 8 Mean maize density (plants/ha) at four commercial dairy farms. Standard error of means shown as error bars.

Available soil moisture varied between sites. Bushy Park had the highest amount of

available soil moisture, however there was strong evidence of over-watering early

during the crop establishment and it is expected that waterlogging conditions

contributed to seedling loss (Plate 3).

18

Plate 3 Low lying area affected by waterlogging during establishment at Bushy Park.

Eleven distinct irrigation events are clearly displayed for the Flowerdale crop and soil

moisture was most optimally maintained at this site. The Sassafras crop experienced

significant moisture stress from mid-December and only two early irrigation events

were observed. This was due to the grower having insufficient water from December

onwards to irrigate his maize crop. The dryland maize crop at Mella had sufficient

available soil moisture to support optimal crop growth between November and the

middle of February, after which, the soil moisture became limiting.

19

Figure 9 The soil water potential of maize crop grown at Mella (a), Flowerdale (b), Bushy Park (c) and Sassafras (d) at a depth of 15cm (-), 30cm (-) and 45cm (-).

Growing degree days

Because of differences in the growing season for maize across regions, growers

require a method of accurately rating the maturity of their crops to assure maximum

yield and quality. For this reason, many hybrid seed maize companies rate maturity

on the basis of "Growing Degree Days" (GDD) or "Heat Units." Because a maize

hybrid requires a specific number of GDD to reach maturity regardless of the number

of days taken to accumulate them, this method is more accurate than the traditional

"Days to Maturity" method.

GDD are calculated by taking the average of the daily maximum and minimum

temperatures compared to a base temperature, Tbase, (usually 10 °C). As an

equation:

GDD are typically measured from the winter low. Any temperature below Tbase is set

to Tbase before calculating the average. Likewise, the maximum temperature is

0

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27-Oct-06 17-Nov-06 08-Dec-06 29-Dec-06 19-Jan-07 09-Feb-07 02-Mar-07 23-Mar-07Soi

l moi

stur

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ia

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25

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27-Oct-06 17-Nov-06 08-Dec-06 29-Dec-06 19-Jan-07 09-Feb-07 02-Mar-07 23-Mar-07

Soi

l moi

stur

e po

tent

ial (

cb)

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Soi

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stur

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cb)

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Soi

l mos

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a b

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20

usually capped at 30 °C because most plants and insects do not grow any faster

above that temperature.

For example, a day with a high of 23°C and a low of 12°C would contribute 7.5 GDD

A day with a high of 13°C and a low of 7°C would contribute 1.5 GDD.

Maturity rating for the hybrid maize variety 38F70 is 630 GDD and 1190 GDD for

silking and maturity respectively (Alex Ford, pers. comm. 2006).

If comparing all six field site locations and taking planting date as the 21st October

and harvesting dates as 21st March the accumulated GDD for these sites for maize

would be 1090, 996, 982, 941, 852 and 851 for Bushy Park, Sassafras, Flowerdale,

Mella, Ridgley and Elliott, respectively (Figure 10).

21

0

200

400

600

800

1000

1200

Oct/06 Nov/06 Dec/06 Jan/07 Feb/07 Mar/07 Apr/07

Bushy Park Elliott

Flowerdale Mella

Sassfrass

Figure 10 Accumulated GDD for maize between 21st October and 21st March for Bushy Park, Elliott, Flowerdale, Mella, Ridgley and Sassafras.

For maize to reach a milk line score of 2.5 and/or 33-38% DM for harvest maturity it

is estimated that between 900 to 1000 GDD will be required between the period of

October and April. Figure 11 indicates the growing regions were this will occur and

provides an excellent indication to which areas of Tasmania can reliably produce

forage maize.

22

Figure 11 Climate map of Tasmania that shows how effective temperature (growing degree days) varies from region to region across the state. Source www.dpiw.tas.gov.au

Costs of production

The average cost of production of maize was $2,553/ha and this equated to an

average cost per kg of DM of $0.17. Ground preparation and sowing had an average

cost of $747/ha and the average fertiliser cost was $656/ha. Harvesting costs

equated to an average of $761/ha, however, this was strongly influenced by the yield.

23

The average harvesting cost per t DM produced was $47, or approximately $15 per

tonne of fresh weight produced.

Table 8 A summary of the cost of production of maize monitored on four commercial dairy farms.

Maize


Cost ($/ha)

Ground preparation

and sowing 1081 505 720 680 747

Fertiliser 736 471 775 640 656

Pesticides 43 259 397 130 207

Irrigation Nil 60 259 300 206

Harvesting 883 665 1336 650 884

Any other costs 109 109

Total costs of

production ($/ha) 2853 1960 3487 2400 2675

Costs of production

(cents/kg DM) 18.0 15.3 15.1 19.2 16.9

24

Feed quality

The DM% percentage of maize varied between 26.3% at Bushy Park and 33.4% at

Mella (Table 9). It is important to note that actual harvesting of the maize at both

Bushy Park and Flowerdale occurred approximately 1 to 2 weeks after the yield

assessment was undertaken, while at Mella and Sassafras harvesting occurred 1 to

3 days after yield assessments were undertaken.

The average ME was 9.9 MJ/kg DM with a range of 9.2 to 10.6 MJ/Kg DM. The mean

CP concentration was 7.4%. The average NDF% and ADF% of the maize was 47.4%


Table 9 A summary of the herbage quality of turnips monitored on four commercial dairy farms.

Maize

Mella Sassafras1 Flowerdale1 Bushy Park Average

Feed quality

Dry Matter (%) 33.4 30.0 29.2 (36.3%) 26.3 29.7

2ME (MJ/kg DM) 10.6 9.7 9.2 (10.7) 10.1 9.9 DMD (%) 74.3 69.1 66.1 71.1 70.2

CP (%) 7.1 7.6 6.2 (6.7) 8.7 7.4

NDF (%) 41.9 50.7 50.5 (49.0) 46.5 47.4

ADF (%) 22.6 26.2 30.6 25.7 26.3

1. Feed quality of maize silage test following ensiling given in parenthesis.

2. Metabolisable energy (ME) values estimated from predicted DM digestibility (SCA, 1990).

25

Discussion Tasmania has a mostly temperate maritime climate. Pastoral areas are dominated by

perennial cool season grasses which are most productive in spring with reduced

growth in summer. This bimodal distribution of pasture growth results in feed gaps

and fodder crops have been used to supplement both the quantity and quality of the

feed available in existing pastures. These forage crops are usually planted as part of

a pasture renovation program, with the cost of renovation offset against the additional

forage produced. There are a number of forage crops appropriate for use in

Tasmania and this study has successfully monitored the on-farm yields, feed quality,

water use efficiency and cost of production of irrigated maize and turnips on

commercial dairy farms.

On farm maize yields varied between 13 and 23 t DM/ha with an average cost of

production of 16.9c/kg DM. In comparison turnip yields varied between 8.0 and 11.0 t

DM/ha with an average cost of production of 7.6c/kg DM. Turnips were shown to be a

very high quality feed with 90% digestibility, 13.3 MJME/kg DM , 16.5% crude protein

and low fibre (26% NDF). In comparison, maize had a lower digestibility (70%), lower

energy (9.9 MJME/kg DM), lower crude protein (7.4%) and higher fibre (47% NDF).

The low crude protein levels in maize means a protein supplement will be required if

maize silage forms a substantial part of the cow's diet.

If forage crops are grown on the dairy farm they will replace pasture which is the

cheapest source of feed. Farmers considering growing a forage crop must decide

whether the crop will be cost effective. Is the extra dry matter from the forage crop

sufficient to offset the pasture foregone and the additional growing and harvest

costs?

Dairy benchmarking figures show that pasture produced on Tasmanian farms costs 7

cents per kilogram of DM on average over the year and grain currently costs

Tasmanian dairy farmers over 35 cents per kg DM. When the cost of resowing the

paddock after growing forage costs is taken into account, turnips will be more

expensive to grow than pasture but will be cheaper than purchased grain (Table 10).

26

Table 10 Partial budget of the costs of growing turnips when they replace pasture

Good pasture Poor pasture

Turnip yield, tonnes DM/ha A 9 9

Irrigated pasture DM foregone, t DM/ha B 7 3.5

Extra yield from turnips, t DM/ha C= A - B 2 5.5

Turnip growing costs /ha $780 $780

less pasture costs saved /ha $580 $460

plus pasture resowing /ha $460 $460

Total additional turnip costs /ha D $660 $780

Cost of extra turnip yield, cents/kg DM D/C 33 cents 14 cents

The above partial budget indicates that it is not cost effective to replace productive

pasture with turnips but if the pasture is in need of renovation there is a role for

turnips in the pasture renovation program. The budget shows that if a pasture has

deteriorated and is yielding only 50% of a productive pasture, then planting turnips

prior to resowing the pasture would produce additional feed of 5.5 tonnes DM/ha

costing around 14 cents/ kg DM. This additional feed would be cheaper than buying

grain. In addition, if the cost of pasture renovation is not included as a cost of growing

turnips (as you may need to renovate the pasture anyway) the costs of growing

turnips falls to only 6 cents/kg DM/ha, which is cheaper than growing pasture.

Maize is a more expensive forage crop than turnips but if it is grown as the first step

in a renovation program for poor pasture the additional feed will be cheaper than

grain. In addition, the maize can be stored and used when required while the turnips

have to be grazed off when they mature. One of the farms that was monitored, grew

maize as a cash crop and the harvested maize was sold to a nearby dairy farmer at

$200 per tonne DM plus transport. Another of the monitored farms grew maize on an

irrigated run off property that was close to the main dairy farm. Maize fits well into the

niche of a cash crop that can be sold to nearby dairy farmers or as a crop for a

nearby irrigated property that is cut off from the main dairy and not grazed by the

dairy cows as demonstrated by the partial budgets shown in Tables 11 and 12.

27

Table 11 Partial budget for maize grown as cash crop and purchased by the dairy farmer.

18 t DM 24 t DM

For grower

Income@$200/t DM $3,600 $4,800

Harvesting costs $990 $1320

Net income/ha $810 $1,680

For dairy farmer

Purchase maize $3,600 $4,800

Transport, say $30/t DM $540 $720

Silage stack $200 $200

Total cost $4,340 $5,720

Cost/kg DM $0.24 $0.24

Table 12 Partial budget for maize grown on run-off area by the dairy farmer

Area 1 Area 2

Maize yield, (t DM/ha) 18 24

Pasture foregone 4.2 6.0

Extra feed 13.8 18.0

Milk response at 60g MS/kgDM $4,471 $5,832

Maize growing and harvesting $2,790 $3,120

Less pasture irrigation foregone $140 $220

Less pasture fertiliser foregone $170 $220

Plus pasture re-sowing $200 $200

Extra income from maize, $/ha $1,791 $2,952

28

It was concluded that maize and turnips do not appear to be cost effective if grown to

replace productive pasture on the dairy farm. If however, these paddocks are poor

producing and require renovation, both maize and turnips are economically viable

options to include as part of this renovation. In addition, if water is a limiting resource

on the farm and some of the irrigated pasture paddocks are likely to be unproductive,

both maize and turnips will provide significantly more feed per unit of water than

these pastures. The results demonstrated in this study have shown that both turnips

and/or maize can be successfully grown as a forage crop by dairy farmers aiming to

increase their farm profitability and can be used as a means of improving the

robustness of their farming system by reducing the reliance on brought in feed and

making better use of available water resources.

29

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Experimental Agriculture 41, 37–44.

Moran, J (1996). Forage conservation. Making quality silage and hay in Australia.,

Agmedia. Melbourne.

Rawnsley, RP, Donaghy, DJ, Christie, KM, Chamberlain, PL, (2006) ‘Yield and water

use efficiency of seven summer forages under irrigation in northern

Tasmania’, Proceedings of the Australian Dairy Science Symposium Vol 2,

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