Last week of Horticulture Level 4

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Frost and fog at Bannockburn campus

This was my last week at Central Otago Polytech! Horticulture level 4 is complete. All that’s left to do is celebrate! And fill in this blog with the week’s activities.

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Practice knot using #8 high tensile wire

On Monday we had a tutorial on fencing. Trevor took us through the basics of lining up a site, positioning posts, wires and how tension and strainer posts work.

For the practical part we tried out some wire knots. The first one was the end post tie off knot (in photo above and diagram below).

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And the figure 8 knot to join two wires together.

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The next topic covered this week was frost. This completes the climate and weather modules. I really enjoyed this topic. Frost is one of the things that can majorly impact your crop with immediate results – and not in a good way! If something goes wrong with your frost fighting system or you misjudge the weather you could lose your whole crop in a few minutes.

Cromwell usually gets around 10 – 12 frost events during spring. This is when you need to have a system in place to protect all the fresh, vulnerable growth. Common methods are wind machines that draw down warmer air from the inversion layer above and overhead sprinklers that freeze water around the outside of a plant, creating latent heat that keeps the plant from freezing inside the ice layer.

Helicopters can also be used to push warmer air down from the inversion layer, but this would be a very expensive way to protect from frost on a regular basis.

Older methods of frost fighting include orchard heaters. Man, do these things put out some heat!

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It is a diesel burner that puts out an amazing amount of heat with the vents all open. You would have them closed during normal use. You need about 50 per hectare to keep the temperature up over the area. Although they aren’t expensive to buy, they do use a lot of fuel so could be expensive overall.

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Me – spur pruning the pinot noir

The rest of the week was spent pruning the last of the fruit trees at the Kawarau Gorge and working on some tools with Trevor in the workshop.

It’s been a great year and I’m so glad I did this course. I’ve learnt so much and am excited to put it to use in the real world. Now on with the job hunt!

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Term 2 – Week 7 & 8 – Pruning

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Winter sunrise over Alexandra

At this time of year the major job going on across vineyards and orchards is pruning. It can mean some very chilly starts!

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Pruning the Bannockburn campus vineyard

Setting up the vines/trees for next seasons growth is essential for crop management and maximising yields.

In New Zealand grapevines are mainly spur pruned or cane pruned on a trellis system. There are so many different ways it can be done though.

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The main different between cane and spur pruning is that with cane pruning you are cutting off nearly all of last year’s growth and laying down two canes (shoots) to act as the arms of the vine. With spur pruning the arms (cordons) stay in place permanently and the shoots are cut back to new buds.

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Before spur pruning

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After spur pruning

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Close up of a gnarly spur

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Before cane pruning

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After cane pruning

There are advantages and disadvantages for both. Spur pruned vines can lose their fruitfulness over time; cane pruning doesn’t since you’re laying down young wood each year. Also, since cane pruning removes most of the old wood it removes disease and pest damaged wood. Spur pruning is a lot quicker and easier to teach, but you may need to spend more time and labour on canopy management later.

Only one more week to go!

Last two week’s weather:

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Term 2 – Week 6 – Soils & Fruit Tree Pruning

This week was split between soil science and fruit tree pruning.

Soil science delved further into soil creation (pedogenesis), looking at the influence of parent material, topography, climate, soil organisms and time. I won’t go too much into that except to say they all play a role in how a soil forms.

We also learnt more about cation exchange capacity of a soil and its water and nutrient holding capacity.

Clay particles and humus are negatively charged, attracting positively charged nutrients in the soil. They will be held in the soil and not leached out. The acidity of the soil (concentration of hydrogen ions) controls which nutrients will be forced off, back into solution in the soil.

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Clay will sometimes have a positive charge but phosphate will snag them all leaving sulphate and nitrate anions to be lost by leaching if not taken up by the plant right away.

In sandy soils the macro pores are too big to retain much water. It pretty much drains straight through taking nutrients with it. Clay and humus can improve the structure of the soil, providing more micro pores that hold onto water.

This is where the water holding capacity of the soil comes in. You only want to irrigate to field capacity – the point where the soil is holding as much water as it can without leaching.

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Nitrogen is the nutrient that is lost most easily from the soil. Aside from traditional fertilisers, nitrogen fixing plants can be helpful to add nitrogen to the soil. Plant roots and bacteria in the soil form a symbiotic relationship where the plant provides energy for the bacteria and the bacteria provide nitrogen to the plant. When that plant dies and breaks down in the soil other plants can then take up the nitrogen.

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We’ve come full circle now and are back to pruning – this week we’ve started pruning the fruit trees at Bannockburn Road. Pruning when trees are dormant means there will be a flush of new growth in spring. If you want to make a cut to a tree without encouraging growth you need to do it in summer.

Apricot trees are trained to grow in a vase shape, cutting back last seasons growth 2/3rds to an outside bud. This lets as much light into the centre of the tree as possible. Also taking out any diseased wood, branches growing in or crossed over.

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Pruning apricot trees – Karen and Praneel

Last week’s weather:

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Term 2 – Week 5 – Soil Science

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View of some terraces in the distance at Bannockburn, Kawarau River

This week we got stuck into soil science with Roger. There were several lectures and trips out and about to sample some different soil types. Surprisingly, this has been one of my favourite topics so far. I think that’s due to Roger’s wealth of knowledge about soils and horticulture.

So far we have covered the components that make up soil, soil development and horizons, structure, texture, nutrients and soil classification systems.

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Roger + spade = soil science

Soil is made up of organic matter, minerals, air and water. Organic matter provides nutrients for soil organisms and plants, gives the soil structure and increases the water holding capacity.

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The size of soil particles creates the soils texture. Sand is considered the largest particle, sandy soils are free draining and don’t retain water. Irrigation can be an issue. At the other end of scale is clay. Clay particles are tiny. There are micro pores between particles that hold onto water and nutrients making them unavailable to plants. Probably the easiest soil to manage is a mixture of all 3 types, sand, silt and clay. That’s called a loam soil.

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Texture triangle

This chart works out what sort of texture a soil has. If your soil has 60% sand and 10% clay it is a sandy loam. As you can see it doesn’t take much clay in the soil for it to be considered a clay. A 50% clay and 50% silt soil is still called “clay”.

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Different soil textures

Above are some photos from our outings to find different types of soil. At the top we have silt and clay soils.

Bottom left is an example of a gley soil. Organic matter sitting over the top of clay (O horizon over a C horizon). It has no drainage and is very water logged. This means the soil will be anaerobic, with none of the normal soil organisms to break down the organic material. Apparently a lot of the farmland in Canterbury was like this before the land was cultivated and drainage was sorted out.

Bottom right is an example of a semi-arid soil that has had irrigation. Semi-arid is probably the most common soil type in Central Otago. This soil develops where the climate is very dry. It’s low in organic matter (so lacking in nitrogen) and can have high salt accumulation since there has been little rain to wash it out.

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The nutrients a plant needs are broken down into macro and micro. Macro are nitrogen, phosphorus, potassium, sulphur, calcium, magnesium, carbon, hydrogen and oxygen. Micro nutrients are boron, chlorine, copper, iron, manganese, zinc and molybdenum. Basically, without all these in the right quantities the plant will have poor growth and poor fruit. In some cases too much can be just as much of an issue as too little.

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In this week’s propagation class we did lily scaling – the process of dividing lily bulbs to end up with more plants. They are dormant for winter now so can handle being dug up and broken to bits. You just snap the scales off at the base and pop them in a plastic bag with damp vermiculite. They get stored on the heat bed. You could do this at home using the airing cupboard. Here’s what the flowers look like:

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Lily regale

We also dug up some of the peonies and divided them as well. They are quite freaky looking! It’s hard to know where to start.

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Peony tubers ready to be divided

The flowers are gorgeous in the summer though, so it’s worth it. Here’s a photo of the peony garden I took at the end of last year:

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Last week’s weather – a lot of minus temps in the minimum columns!

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