Lucerne in Australia(Success stories)

Relevant to: CMT

Drip Irrigation of Lucerne

Drip irrigation is the application of droplets of water to a particular crop through emitters which are located in a pipe, or dripperline. In the case of sub surface drip irrigation, the dripperlines are located underground, at a depth dependent on the root zone of the crop and characteristics of the soil.
 
In a sub surface irrigation system growing lucerne, the spacing of the dripperlines, or “laterals” can be anywhere from 0.6 metres to 2.8 metres. The precise spacing depends on the requirements of the crop and the ability of water to move laterally through the soil. Generally, in a sandy soil the laterals will be closer than in soils with a higher clay content.
 
System Installation
In the first instance, a sub surface irrigation system must be designed. The design of a sub surface irrigation system will incorporate such factors as pressure required at the source, filtration required (based on analysis of water quality), the level of operating flexibility required and the maximum daily crop water requirement.
 
The laterals in a sub surface drip lucerne system are commonly laid at a depth anywhere from 200mm to 400mm. There are a number of implements for laying the dripperlines, generally they are attached to rear of a tractor and have a number of wheels for holding the reels and a tube attached to a tyne.  
 
The system is a combination of pumps, valves, filters, fertigation equipment, vacuum breakers and laterals. A good design is essential to the successful operation of the system.
 
Crop Water Requirement
The water requirements for a particular crop can be established by calculating the evaporation rates, plant transpiration and crop coefficients. These calculations give a rate of evapotranspiration, and from that crop water use can be worked out.
 
Evapotranspiration is the combination of water transpired from vegetation and evaporated from the soil and plant surfaces.
 
Crop coefficients are used to estimate plant water use, under non limiting soil moisture conditions. Different crops at different stages of growth have their own particular water requirement. Lucerne is the reference crop for crop coefficient data, so an average growing lucerne crop in the middle of the season has a crop coefficient of 1.
 
Crop Water requirement = crop coefficient x evapotranspiration
 
Table1. Lucerne crop coefficient data
 

Growth Stage
Lucerne Crop Coefficient (Kc)
Early season
0.4 – 0.8
Mid season
1 -1.2
Late season
1- 1.15

 
Water budgets can be prepared using the average evapotranspiration figure, average rainfall figures and crop coefficient data. From this, an estimate of water required to be applied for a season can be made. The water budget is a guide – irrigation decisions are made on the basis of actual figures and observations during the season. An example of a water budget is in the case study section.
 
 
Scheduling is an important part of irrigation. Different soils in areas with different climatic conditions require unique combinations of irrigation frequency and run times. A sandier soil where water flows downward but not laterally in the profile may require a series of more frequent short irrigations, while a heavier soil may require longer irrigations further apart.
 

Nutrition

Crop requirements
Lucerne crop nutrient removal (per tonne)
Nitrogen (N): 20–30
Phosphorus (P): 2-3kg
Potassium (K): 15-20kg
Sulphur (S): 2-4kg
 
If the plant is nodulating correctly, it will fix (convert from the atmosphere) most of the nitrogen it requires. In situations where high yields are being sought, some nitrogen fertiliser is applied. The amount of phosphorus and potassium fertiliser applied depends on existing levels in the soil.
 
An application of molybdenum can assist lucerne plant to nodulate effectively.
Fertigation
Sub surface drip irrigations systems have the advantage of fertigation – the application of plant nutrients through the irrigation system. Fertigation allows for the nutrients to be applied directly to the root zone and in smaller amounts more frequently. This has positive effects for plant growth because the plant receives the exact nutrient requirement at the correct timing. Fertigation also limits the environmental impact of fertilizers on the environment – both through limiting the leaching of excess nutrient through the soil profile to the water table and the return to the atmosphere of applied nitrogen fertiliser, which can become damaging greenhouse gases. Liquid fertilisers or dissolved soluble products can be injected into the irrigation system using fertigation equipment such as a venturi, a “dosatron” hydraulic pump, or a positive displacement injection pump. An example of a fertigation program is in the case study.
 
Case Study: Brett Dixon
Brett Dixon is a dairy farmer in Merrigum, northern Victoria. He has 24 ha of lucerne grown on a sub surface drip irrigation system. He sowed the semi dormant Pioneer L56 variety at a rate of 22kg/ha in late September 2007.
 
The laterals are buried at a depth of 200mm, and are 1 m apart. The emitters have a flow rate of 1 litre/hour, and are spaced every 0.5 m along the drip line. This system gives an application rate of 2mm of irrigation water per hour.
 
Brett Dixon:
“My system is controlled by an NMC automatic controller. This gives me the ability to set a one or two week irrigation program, and have the NMC automatically run the system on the days and for the run times I specify.”
 
“Typically in the November and early December period, I run the system twice a week for 10 hours each irrigation. This gives the crop 24 mm of water for the week. The average evapotranspiration for his area at this time of year is 5 mm per day, and the crop coefficient for lucerne is 1, so the crop water requirement is 30mm per week. With some effective rainfall and existing soil moisture, I am irrigating to the requirement of the crop.”
 
“In January and February, the temperature normally increases, and therefore so does the evapotranspiration. The average is 6 mm per day, and normally I run the system every second day for 6 hours.”


“If it is really hot the daily figure can reach 14mm. On days like this my system needs to have the ability to keep up with the crop water requirement, and apply 14mm. My system can do this – I can run two shifts for 11 hours in one day, so I could apply 22mm if I needed to.”
 
“The best thing about the system is the ease of operation. I just program the NMC controller at the start of the week and leave it. It turns itself on and off. There is some maintenance required – flushing and cleaning, but in terms of time required it is very small compared with my flood irrigated blocks.”
 
“This year, in the second year of the lucerne stand, I achieved a yield of 24 t/ha dry matter, using 7 megalitres of water. With some better scheduling and more fertiliser, I believe I can get 28 – 32 t/ha next year.”
 
Site by mantis.