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30 October 2019 Jay Howes

Different soil types require unique management

This is the third article of a three-part series that takes a closer look at New Zealand soils. This month, I focus on the different management strategies that are required for the four distinct soil types that were discussed in the last issue.

New Zealand soils are generally young (comparatively worldwide), made from inherently different parent materials of different origins. Soil types have varying nutrient availability and respond to applied fertiliser uniquely.

Pumice soils
Pumice soils can recover quickly from intensive grazing, and soil compaction of the topsoil is usually not a problem. However, protecting them from pugging damage is important as they can erode  easily if the pasture is exposed by stock. Cultivation should also be kept to a minimum. These soils are loose, friable, and have a low bulk density which makes them perfect for low/no till methods of planting. Pumice soils are naturally deficient in Phosphorus (P), Potassium (K), Magnesium (Mg) and Sulphur (S) and always need yearly applications of these nutrients if they are to remain  productive. Cobalt (Co) and Selenium (Se) are two trace elements that are lacking in pumice soils and need to be added to yearly fertiliser applications. 

Organic/peat soils 
These soils usually need  some kind of artificial drainage to be productive. Over drainage (drains that are too deep) of these soils can make them dry in summer. This can cause subsidence (sinking soil), poor summer growth and hydrophobicity. By keeping drains shallow and/or controlling the water table, you minimise many of these problems. As for pumice soils, cultivation should be kept to a minimum, and low/no tillage methods are recommended. These soils have high cation exchange capacities, and a naturally low pH. Accordingly, they need larger lime applications to increase or maintain pH than other New Zealand soil types. As these soils often have small amounts of mineral material, nutrient deficiencies are common, especially P and S and some trace elements.

Sedimentary soils
This soil type is the most common soil in New Zealand. It is no surprise it is comprised of many soil orders and groups. So the  management of these soils can only be described at a generic level.  Some sedimentary soils naturally provide considerable amounts of K (from soil clay minerals) for plant growth. Some of these soils are unlikely to require capital applications of K and may not even  require maintenance K applications. Sedimentary soils tend to have medium-to-low Anion Storage Capacity (ASC), and therefore require lower rates of maintenance or capital P fertilisers compared  to other soil types. Given the low ASC, they tend to be responsive to S fertiliser in the spring, especially after a wet winter. Some sedimentary soils are poorly or imperfectly drained and prone to soil damage from grazing animals. Cultivation also has to be carefully timed to avoid soil damage as these soils take longer to dry out than other soil types. Some sedimentary soils can be low in  Molybdenum (Mo) and need periodic applications of this nutrient to ensure optimal clover growth. 

Ash soils
Ash soils include some of New Zealand’s most productive soils, and have naturally good soil structure and bulk density. These soils tend to tolerate the impacts of machinery and grazing animals better than other soil types. Cultivation still needs careful management to preserve topsoil structure, as some of these soils have limited workability when wet. Ash soils generally have naturally low levels of K, and can respond well to K fertiliser. These soils usually have a higher ASC than the other soil types, and therefore need larger amounts of maintenance and capital P fertiliser compared to the other soil groups. These soils also generally tend to have higher sulphate-sulphur levels, again due to the higher ASC.

For more information on your property’s soil type or to arrange a soil test, talk to your local PGG Wrightson Technical Field Representative.

Jay Howes

Related Articles

Precision placement worth it

01 October 2019

what can be achieved when swedes receive a bit of T.L.C. is impressive. Treating a crop of swedes with a similar precision to that of fodder beet has been delivering some good results in Southland and more recently in other traditional winter crop areas across the country.

What started as a trend with contractors who were looking to extend their season with precision drills by sowing swedes, has now developed into a precision sown pelleted swede market for farmers wanting to get greater swede yields.  

To allow the precision placement of swede seed through precision drills, PGG Wrightson Seeds uses Ultrastrike® pelleted swede seed, a weighted build up seed coating with Splitkote technology. PGG Wrightson Seeds Sales Agronomist, Brian Young says it is smart technology, not just a matter of putting a coating around the seed to increase the size. “It takes little moisture to germinate the seed as it absorbs moisture from the soil and air, then the seed swells up and splits the coat. We have found over the last two to three years that it germinates as well as, if not better than, traditional seeds in dry conditions.”

Sown at 90,000 seeds per hectare, or 22 cm seed spacing in 50 cm rows, Ultrastrike® pelleted swede seed delivers approximately 350 g per hectare of swede seed, compared to conventional sowing rates of 800 to 1,000 g per hectare. The precision placement of that seed results in an evenly distributed crop that allows bulb yields to be maximised.

In practical terms, it is a way to increase swede yields if you are prepared to spend a bit more on paddock preparation and pelleted swede seed. PGG Wrightson Technical Field Representative, Allister Gauldie has had some good success with clients using Ultrastrike® pelleted swede, growing an exceptional Clutha Gold crop that won a local Wyndham winter feed competition (pictured here). “I have been really impressed with the tonnage we can achieve when we treat swede crops like fodder beet. Paddock preparation is important with precision sowing, as is ongoing monitoring. We are sowing fewer seeds per hectare which means we can’t afford to lose plants to insects and weeds, so it is important to be proactive with monitoring,” says Allister. 

Precision sown swedes is gaining traction with farmers who are wanting to put more focus on better yielding crops to reduce their cents per kg DM of feed grown. Brian says, “often we can focus too much on the up-front cost, but the reality is, if we can grow an 17,000 to 19,000 kg DM per ha crop for $1,400 ha, then that is 7 to 8 cents per kg DM which is a cheap source of feed.” 

PGG Wrightson Seeds has three Ultrastrike® pelleted swede varieties, Cleancrop™ Hawkestone swede, Clutha Gold and Major Plus that are available this spring. Talk to your local PGG Wrightson Technical Field Representative to see if precision sown pelleted swedes could be an option for you. 

Supplied by PGG Wrightson Seeds


Controlling yellow bristle grass

01 November 2019

I am receiving an increasing number of calls from across the North Island especially the Waikato and Manawatu, about Yellow Bristle Grass (YBG) being found in both pasture and crops, and more particularly maize.

This weed is part of the family of annual grasses known as Seteria, which includes foxtails and millets. YBG originally came from Asia and has spread through Europe, North America and Australasia.Over the last few years, possibly driven by wet winter pugging,

YBG has spread through Taranaki, Waikato, Auckland and the Bay of Plenty, moving from roadsides into paddocks.

YBG does not provide good quality late summer/autumn feed. It is a C4 photosynthetic plant that grows more vigorously at higher temperatures than ryegrass. It becomes dominant through the summer months, reducing the quality of your pasture. Then with winter frosts, the YBG dies out leaving gaps for weed and more YBG infiltration the following spring. 

Germination of YBG seeds typically starts around mid-October when soils are about 16 degrees Celsius and peaks by mid-November when soil temperatures are over 20 degrees Celsius. This is a  similar timing to other C4 weed grasses, such as summer grass, crowsfoot grass, and smooth witchgrass, however due to the size and seed numbers per plant, YBG is far more invasive and  competitive.

The seed heads can normally be seen from late December onwards, but more commonly through January and February. Once these seed heads appear, the seeds are viable and cannot be killed by sprays. Seeds are hard coated and dispersed in water,in hay, on animals and in contaminated crops such as maize. They are dormant for about three months before they can germinate. Germination is driven by soil temperature, so usually new germination doesn’t happen until the following spring. The seeds can last in the soil for up to ten years, although generally only viable for just a few  years.

Because YBG and other weed C4 grasses readily invade run-out or pugged pastures, the best form of control is not to get into the situation in the first place. Avoid allowing flat weeds to dominate and then spray them out, as this leaves a bare patch in the pasture for weeds including grasses to invade.

Top control tips

  • Learn to identify YBG and how it differs from other summer grasses, especially at the vegetative growth stage. One of the most recognisable features of YBG is a bright red stem base. Once identified, you can then isolate the area and treat accordingly.
  • Avoid pasture damage at the key germination timing, from October to December.
  • Remove seed-heads through topping during the summer or tight grazing before the seed-heads appear. Seeds pass through the rumen and land on the ground in a pile of dung ready to germinate the following spring.
  • Spray non-selective herbicide, such as glyphosate, before seed-heads are produced.
  • Whether the YBG is in pasture or crop, for example maize or brassica, there are selective herbicides available that kill the YBG and other summer grasses before they go to seed-head preventing damage to your pasture or crop. Speak to your local PGG Wrightson Technical Field Representative for guidance. 
  • YBG seeds can be killed in a good quality silage pit where increase in temperature and the correct acidic conditions are created during the ensiling process.

For more information on YBG control, get in touch with your local PGG Wrightson Technical Field Representative.


Weed control in new pastures

01 November 2019

New pastures are a great opportunity to lift production and fine tune the production dynamics on your farm.

After sowing your new pasture paddocks, ensure you monitor them as they emerge. Once the clovers are at the two trifoliate stage, it is a good time to assess the weed pressure. Some paddocks can be clean during establishment but many have a resident weed population that emerges at the same time as sowing down the new pasture. Checking the paddock at this early stage allows selection from a range of herbicides that can prevent the weeds competing for nutrient, moisture and light.

Weeds are much easier to control when they are small, so once your clovers have got two trifoliate leaves, check the paddock for weeds. Identifying the weeds at this early stage can be tricky but I  recommend a copy of “A Guide to the Identification of New Zealand Common Weeds in Colour” by E. A. Upritchard. This little red book is a good investment to have in the truck, and shows the most common weeds at the seedling stages. Identification of weeds is required so the correct herbicide can be selected.

A couple of common weeds seen in new pasture are shepherd’s purse and spurrey/yara. Both these weeds have distinctive characteristics. The shepherd’s purse seedlings have distinctive white hair on their leaves in a cross shape, these can be seen with a hand lens. Spurrey/Yara is an interesting weed, the seedling has upright, round leaves which can be mistaken for grass, but it has a distinctive pattern of four upright leaves originating from the stem above ground level. As with many weeds, spending time to get to know them helps with identification. I suggest if you would like some help identifying weeds, contact your local PGG Wrightson Technical Field Representative.

Weeds in pasture often show up where the gaps are. If you have used weed control and left open areas, use some more seed to fill in those gaps and prevent the weeds establishing. This can sometimes happen, even in new pastures where something has gone wrong during establishment.

If your new pastures are patchy with large gaps, consider using the drill to fill in those gaps because weeds do not provide much in the way of value feed for your stock compared to modern productive grass species. Contact your local PGG Wrightson Technical Field Representative who can help.

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