Newsletter - July 2009

July 2009

There is a positive to the long period of very slow grass growth that started for many at the end of March. And growth has been slow with some pasture cuts indicating growth of less than 10kgDM/ha/day for both May and June. 30kg/ha/day was recorded on the monitor property near Edgecumbe for May but down to 10kg for June.

While little has been happening above the ground, a steady increase in root development is taking place.
It is the mass of root that largely dictates the amount of pasture grown throughout the major growing season. Districts that experience the coldest winters usually have the greatest growth in spring.

On friable, humus rich, well-drained soils, roots will be apparent to a depth of 0.8 metres
(2.5 feet). Careful digging provides a wealth of information.

A check of areas that have been damaged in wet weather and non-damaged areas is likely to provide a clue to the amount of growth that can be expected from each area. More root mass generally means more feeding potential and more total growth.

Worm counts are useful and it often takes careful breaking of the uppermost root mass to extract all worms. 20+ in a 9 inch cube is usually regarded as a pass mark however fewer than twenty worms does not mean the soil is not strongly biologically active.

In pasture worms come in three major categories, surface workers, mid range workers, and deep burrowers.

Worms are macro processors and have the function of rapidly breaking down litter, dung, and dead root. During the first winter after a DoloZest or CalciZest application in excess of 70 earthworms per spade cube have been counted.

In soils where there is subsoil suitable for worms to retreat to during summer 20 –25 worms is normal.

All earthworms are oxygen breathers so compacted poorly drained soils contain many fewer than well aerated freer draining soils.

Over time DoloZest/CalciZest based programmes will break up hard pans. Deep burrowing worms undertake much of this work. The channels made are quite obvious, particularly where there is a distinct colour difference between the topsoil and subsoil.



Potential of Earthworm activity

No.worms       No.worms          Weight            Weight            Weight            N/day         N/year
20x20cm                                   worms            casts/day       casts/year   
spade             /ha                      kg/ha              kg/ha               t/ha                kg/ha          t/ha
1                    250,000                165                  165                   60                  2              0.8
5                    1,250,000             825                  825                  301                 8              3
10                  2,500,000             1,650               1,650               602                 17            6
15                  3,750,000             2,475               2,475               903                 25            9
20                  5,000,000             3,300               3,300             1,205                33           12


Experiments at the Conneticut Agricultural Station have shown that earthworm castings contain approx. 5 times more available N, 7 times more available P, 3 times more exchangeable Mg, 1.5 times more Ca and 11 times more available K than ordinary topsoil.

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Nitrogen Fertiliser and Slow Growth.

There seems to be a direct link between slow growth particularly during winter and the application of nitrogen fertiliser. There may be a pleasing change in colour after the application of N however the major benefit of winter and early spring applied nitrogen comes in late September and October, when growth is often enough to meet requirements without its use.

The extra growth achieved through the application of N fertiliser also comes at a cost.

Excess N application, and that will change from site to site, reduces the amount of N fixed naturally, often physically degrading soil limiting moisture holding ability and the plant roots ability to harvest nutrient and moisture from deeper levels.

Our position is that fertiliser nitrogen applied to a well-structured soil under good grazing management does not increase the total amount of pasture grown but simply alters when it grows.

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From the June 30 edition of Dairy News

US eyes nitrogen war

A $US2.8 million war chest has been established to help US researchers combat the environmental impacts of nitrogen.

Tom Tomich, director of the Agricultural Sustainability Institute at the University of California, says while nitrogen is ‘a hero of the agricultural revolution’, it is increasingly viewed as a worrisome source of water and air pollution.

‘This is one of the most important but least publicised environmental issues we face: escaped nitrogen from agriculture affects the quality of our air, water and soil and has huge potential to contribute to climate change,’ he says.

Tomich says many US politicians and members of the public are unaware of the challenge in mitigating nitrogen’s environmental impact – ‘and many farmers are unaware that nitrogen management can save them money’.