Irrigation Field Day

Transcription

1 Irrigation Field Day for Morven Glenavy Ikawai Irrigators Date Venue 19 th May 2010, 10.15am pm, Fairbank Property, Waihao Back Road Objectives 1. For irrigated farmers (spray and borderdyke) to increase their understanding of irrigation practices to improve pasture and crop production, irrigation efficiency and environmental outcomes 2. To discuss soil, water and plant interactions for productive pasture and crops 3. To demonstrate soil moisture monitoring tools for more productive, efficient and profitable irrigated farming 4. To hear the results of local irrigation research and farm plan trials Programme STOP 1 Calf shed Registration and handouts Introduction and Programme Welcome & Background Farm Information Managing your irrigation well for production and the environment 1. Irrigation management - borderdyke & spray 2. Soil compaction 3. Water quality risks Sue Cumberworth Robin Murphy Dave Houlbrooke AgResearch Farm Walk - Practical irrigation Questions & discussion pm LUNCH 1.00 Irrigation getting the best production and benefit from your water 1. Design, installation and maintenance 2. Management 1.50 Soil Moisture Monitoring Options Questions & discussion Update on Farm Plans Neal Borrie & Joe Powers, Aqualinc Dave Houlbrooke Neale Borrie & Joe Powers, Aqualinc Aquaflex Hydro Services Ben Hart & Nick Ruddenklau MGI moving forward Robin Murphy 2.00 Close This event is being organised by Morven Glenavy Ikawai Irrigation Company Ltd. The AgriBusiness Group

2 Waikakahi border dyke studies Dave Houlbrooke - AgResearch-Invermay. Waikakahi catchment is part of the national best practice dairy catchments study

3 OLD BORDER DYKE EVALUATION Results from an assessment of two difficult to manage old border dyke systems Soil type Temuka Eyre Drainage class Poorly drained Well drained No. of events/yr 7 11 Wipe-off loss 52% (38-62) 25% (5-56) Mean P conc mg/l 0.82 mg/l Annual P loss 3.4 kg/ha/yr 2.0 kg/ha/yr Timing in relation to grazing events and fertilizer application important WIDE LASER LEVELLED BORDER DYKE EVALUATION 3 events measured on 450 m long and 50 m wide (Temuka silt loam) wipe-off ranged from 0-10% of total inflow (c. 90% reduction compared with old borders) P conc. same as for old border wipe-off P load related to volume wipe-off water lost IMPROVED IRRIGATION MANAGEMENT PRACTICE IN THE WAIKAKAHI CATCHMENT Extensive irrigation improvements have taken place over the past 5 years - wide laser levelled border dyke upgrades - conversion to spray irrigation - placement of bunds for stream protection - water reuse (pond and spray) - improved watering times

4 Waikakahi assessment of K-Line use on sloping land Dave Houlbrooke, - AgResearch-Invermay. Site: Sloping landscape on Pikes Point Road. Soil type: Taiko shallow silt loam/fine sandy loam (Pallic soil) Objective: Evaluation of the field performance (distribution uniformity and application rate and depth) of K-Line irrigation using three different nozzle sizes to determine surface runoff risk Soil measurements: Surface infiltration, soil water holding capacity Matching irrigation application rate to soil infiltration rate Three nozzle sizes for K-Line irrigation systems were assessed to determine their application rate, depth and uniformity. The mean application rates for the 3 mm, 2.8 mm & 2.5 mm nozzle sizes were 1.4 mm/hr, 1.2 mm/hr and 1 mm/hr respectively. The surface runoff or overland flow of water as a result of irrigation can be brought about by two different mechanisms. The first process is known as infiltration excess flow whereby the rate of application of water exceeds the soil s ability to infiltrate or take up the irrigation water. The soil s surface infiltration rate at the demonstration site was measured as 99 mm/hr with a standard error of 28 mm/hr. Surface infiltration rate is spatially and temporally variable and can reflect land management practices such as time since grazing and previous pugging damage. However, considering the three different irrigation nozzles tested delivered water at rates less than 3 mm/hr, it is highly unlikely that infiltration excess conditions will occur for this soil type under K-Line irrigation. Scheduling of K-Line applied water to avoid over watering The second mechanism that can cause overland flow of water as a result of irrigation is defined as saturation excess flow. In this case overland flow does not occur until the soil profile is full of water and it cannot drain as quickly as water is being applied. The Taiko shallow silt loam, like most other Pallic soil types, has a drainage limitation in the subsoil that causes water to perch above the fragipan layer. Considering the presence of this fragipan and the low application rate of the K- Line irrigation system, it is likely that over-watering leading to saturation excess conditions would be cause of overland flow generation on this landscape. Given the slope of the landscape and presence of the fragipan, it is likely that much of any excess water applied would move as subsurface flow above the impermeable layer until the point that the slope intersects with the valley floor. Therefore, it is the presence of seepage zones at this point that will identify the likelihood or extent of over watering.

5 Depth and rate of irrigation (mm/hr) Measured soil water parameters for the Taiko shallow silt loam Soil parameter (0-300 mm) Volumetric soil moisture (%) Irrigation depth (mm) Field capacity 34 - Wilting point 13 - Irrigation trigger point 23 - Total available water Readily available water mm nozzle 2.8 mm nozzle 2.5 mm nozzle Pod position Distance along tray transect (m) Application uniformity at 6 m parallel distance down a line of irrigation pods. The poor application uniformity displayed by a line of K-Line irrigation pods needs to be accounted for in order to prevent over watering from the areas of pod overlap and therefore creating overland flow or subsurface flow under saturation excess conditions. A conservative irrigation schedule for the Taiko shallow silt loam on sloping land would be to irrigate less water more often than a full field capacity replacement strategy i.e. 24 mm of the 32 mm of readily available water during any one event. At an average application rate of 1 mm/hr using the 2.5 mm nozzles, water could be applied for a 24 hour period (daily shift). This would provide a further 4% or 12 mm buffer to allow for much of the excess water that will be applied in the application peaks, and thus decreasing the risk of overland or subsurface from over watering. A 24 mm application depth would require an approximate 4-5 day return time during peak evapotranspiration periods if pasture production is to remain unlimited by water availability.

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7 Soil physical quality Dave Houlbrooke, - AgResearch-Invermay. Soil physical quality is important to maintain a healthy soil and pastoral ecosystem. A soil in good physical health can adequately transport and store water & nutrients while physically supporting growing plants and maintain an active biological community. Soil compaction and pugging decreases a soils physical health and places limitations on some of the important functions described above, therefore resulting in potential decreases in forage yield and a greater occurrence of surface runoff generation. Unaffected by compaction Slightly affected Moderately affected Severely affected 0 cm De pth (c m) 10 cm Topsoil is loose and crumbles easily into small, granular aggregates Abundant roots throughout topsoil Worms are common Upper part of topsoil is loose Some larger, firmer aggregates between 10 to 15 cm Roots do not commonly penetrate firmer aggregates Larger, firmer aggregates more common. Sometimes have a horizontal platy appearance. Roots grow around rather than through aggregates Reddish stains along some root channels Lumpy, irregular surface Aggregates are coarse or absent Few roots below 5 cm Reddish stains along root channels. Soil often greyish in colour and may have an unpleasant smell when wet. Few worms present. Pugging vs. compaction Compaction: Occurs when the air space within a soil is compressed by a weight and pressure that exceeds the soil strength resulting in a greater bulk density (mass per unit volume of soil) and decreased pore space. Compaction occurs when large pores are still air filled. Soil compaction can result in a small but long term depression of plant yield potential Pugging: Soil pugging is the molding of wet soil around animal hooves and occurs when soil pores are full of water. Soil pugging can result in an large but short term loss of plant yield potential Critical factors determining soil compaction risk The extent of soil damage under livestock pastoral grazing is dependent on five critical factors: Antecedent soil moisture, Livestock loading (weight/hoof contact area), Grazing intensity (animals/ha) and duration (time on soil), Vegetative cover, Inherent soil properties

8 Change in soil physical quality under land-use intensification in the North Otago Rolling Downlands Dave Houlbrooke & Jim Paton, AgResearch-Invermay. Overview The objective of this research was to assess the effects of irrigation and type of grazing animal on soil quality and forage production under both pasture and crop land-use in the North Otago Rolling Downlands The research site was established in autumn 2004 on a Timaru Pallic soil and contains 32 plots approximately 10 m wide and 25 m long running down the slope. There are 3 levels of treatments replicated 4 times: irrigated vs. dryland, sheep vs. cattle and pasture vs. forage crop. Soil compaction and forage yield

9 kg/ha/yr Surface runoff 0.8 Total P (kg/ha/yr) Suspended sediment (Mg/ha/yr) Proportion contributed by irrigation Sheep pasture Sheep crop Cattle crop Sheep pasture Sheep crop Cattle crop Control Restricted Grazing Aluminium sulphate Cattle Sheep Summary Increasing land use intensity on rolling Pallic soil landscapes has resulted in increased levels of soil compaction and subsequent increases in surface runoff losses. Levels of soil compaction evident in the NORD region have not critically effected pasture growth. Reliable levels of soil moisture are the most critical factor influencing pasture growth in the NORD.

10 Winter forage cropping Dave Houlbrooke, Ross Monaghan- AgResearch-Invermay. Winter forage grazing paddocks are quite leaky for nitrogen (N), phosphorus (P), sediment and faecal bacteria - but does vary according to soil type & slope Mitigation options Restricted grazing Back fencing Riparian management and grazing direction Nitrification inhibitors

11 Farm dairy effluent transport pathways Dave Houlbrooke, Ross Monaghan, Richard Muirhead, Richard McDowell - AgResearch- Invermay.

12 Common Terminology Saturation The soil moisture content at which all of the soil pores are full of water. Any additional water applied to a saturated soil will either pond on the surface or drain through. Field Capacity (FC) The soil moisture content after drainage from an initially saturated condition has become negligible. The macro-pores (big spaces) of the soil are filled with air and the micro-pores (small spaces) hold water by capillary action. Stress Point (SP) The soil moisture content below which plant growth will be limited. Growth slows because the soil is too dry for the plant to extract water fast enough. Permanent Wilting Point (PWP) The soil moisture content below which plant growth will stop. At this point the soil is too dry for plants to extract any more water. Water Holding Capacity (WHC) The maximum amount of water (mm) that can be held in the soils. Not all of this water is available for plant growth. Plant Available Water (PAW) The maximum amount of water (mm) that plants can extract from the soil. It is measured as the difference between field capacity and permanent wilting point within the plant root zone. Soil Water Deficit (SWD) The amount of water (mm) required to restore the soil to field capacity. Effective Root Depth The depth of soil profile that has enough rooting density for extraction of available water. Roots may be found at depths greater than this, but they do not contribute significantly to water extraction. Infiltration Rate The rate at which the soil can absorb water (mm/hr). This rate changes as the wetness of the soil changes. This rate can also change if a soil becomes damaged. Application Rate The precipitation rate (mm/hr) of water onto a soil. This is generally considered as an instantaneous rate (i.e. the rate that water would fall on a person standing directly under the irrigator). Application Depth The average depth (mm) of water applied during a single application. Return Interval The time (days or hours) it takes for an irrigator to make one full round. Application Uniformity The spatial variability of application. This can be defined in a variety of ways, including Distribution Uniformity (DU) or Coefficient of Uniformity (CU). Surface Ponding Water that does not immediately infiltrate into the soil, and collects on the low points of the soil surface. Surface Runoff Water that does not immediately infiltrate into the soil, and runs across the soil surface by gravity. Leaching The loss of nutrients, salts, or biological contaminants due to deep percolation of water beyond the root zone of plants.

13 Soil Moisture Principles Figure 1: Graphical demonstration of soil moisture principles. Figure 2: Example soil moisture and rainfall plot.

14 Irrigation Scheduling The main goals of good irrigation scheduling are to: grow more plant biomass make best use of available water minimise runoff minimise leaching To achieve these goals, irrigation water must be applied: At the Right Depth Apply enough water to keep soil moisture content up above the stress point, so plants can extract it. Try not to apply more water than the soil can hold (i.e. try not to exceed field capacity, and definitely don t exceed saturation). Applying the right depth of water can help avoid both runoff and leaching and will keep more moisture in the root zone, thus making best use of irrigation water and growing more biomass. It is common in many cases for irrigating farmers to have no idea how much water is being applied by their irrigation. Application depth is easy to measure, and should be done for each irrigation unit. Know the farm s soil type and water holding capacity this is critical for choosing how much water to apply. Also monitor the soil moisture (i.e. daily) so that application depth can be matched to the soil moisture deficit on that day. At the Right Rate Application rate should not exceed the infiltration rate of the soil. Otherwise, ponding, and possibly runoff, will occur. Ponding and runoff mean that less water gets into the root zone. Runoff can also mean that valuable nutrients are being lost. Use gentler rates on more dense soils (i.e. clayey or silty soils), and especially on steeper slopes. Again, knowledge of the local soil conditions is important. At the Right Time Ideally, apply irrigation water before the stress point is reached, and definitely before the permanent wilting point (at which point the plants die). Also, do not apply water when the soil water deficit is low (i.e. when the soil is still wet) the soil will not be able to hold most of the water you apply, and ponding, runoff, or drainage will occur. Use an appropriate return interval. This should be based on the soil s plant available water holding capacity (PAW) and typical evapotranspiration (ET) rates. If the stress point is reached before the irrigator comes back around, the return interval is too long. In the Right Place Soil conditions often vary across a property (i.e. different soil types, or shady/sunny areas). This may mean that different areas of the farm need to be irrigated differently. Before applying water, check which areas actually need water, and which areas don t. Also, consider application uniformity. Poor uniformity means a lot of the applied water is not actually getting to where it needs to be (i.e. the root zone of the plant).

15 Tools for Management The following were identified throughout the study as important tools for the wise management of irrigation: - Water Use Monitoring regularly check flow records. - Soil Moisture Monitoring schedule irrigation based on moisture status of the soil. - Soil Temperature take note of soil temperatures in the shoulders of the season. - Record Keeping - compare management decisions month to month, year to year. - Know how to interpret water use and soil moisture information (This is just as important as collecting it!) In Canterbury and Otago, there generally aren t many irrigation management decisions to make during the summer period ET is high and irrigation generally proceeds uninterrupted (until a significant rain). The shoulders of the season are generally where much of the water savings can be made: - Spring Soils are generally near field capacity (full of water), and temperatures are still low. There is good potential to save water by delaying the start of irrigation until it is actually needed, i.e. when a soil moisture deficit occurs and temperatures increase. Where seasonal limits are imposed, saving water in the spring, when ET is low (risk to crops is minimal), will also mean that more water is left for the peak season. - Autumn Evapotranspiration rates can decrease rapidly at this time of year. This means irrigation water doesn t need to be applied as regularly. Minimising unnecessary irrigation in the autumn also helps minimise cooling of the soil, helping to keep plants growing longer. Figure 3: Potential Evapotranspiration (E p ) and Rainfall (P), Lincoln (44 year means, ). (Adapted from Lincoln University SOSC629 course notes, 2010). This demonstrates the change in ET across the year, and the discrepancy between ET and rainfall in the summer.