With the gap steadily closing between the cost of producing a kilogram of milk solids and the amount of money received the arrival of the clover root weevil this season is unwelcome.
Healthy clover in a permanent clover rye grass pasture is capable of fixing more than enough nitrogen for the production of 18’000+ kilograms of dry matter annually.
In the short term applying fertiliser nitrogen seems the only logical solution to the damage caused by the root weevil. A severe root weevil infestation may effectively reduce the amount of clover fixed nitrogen by as much 90%.
This suggests that a little in excess of 200kgN/ha should be applied to maintain normal pasture production.
Urea, the cheapest form of fertiliser nitrogen, is currently $745.00+GST/tonne ex store, which means the cost of 200kgN is $323.91+GST. That’s a cost of $48’586.95 for 150ha without the cost of cartage and spreading, roughly the price of a new ute.
A keen trout fishing neighbour remarked recently that if only he could interrogate the trout he catches he could catch a lot more.
Although it would be useful to communicate directly with clover root weevil it’s not necessary in order to know why they are currently attacking clover in dairy pasture.
It’s not all clover that is dealt to and it’s not just clover in dairy pasture that is affected. Weevil’s don’t know what type of animal is grazing the pasture, so it’s not a problem specific to pastures grazed by dairy animals.
The factor common to most intensive dairy farming is the use of nitrogen fertiliser. In our view regular fertiliser nitrogen always precedes damage by pests.
In pasture the role of pests is to ensure that weakened plants are not able to grow to maturity and produce seed, only the strongest survive which is why not all clover is damaged.
Clovers flourish in pastures as plant available nitrogen declines, hence the application of fertiliser nitrogen reduces the reason for their existence. The plants that do survive struggle to compete with grass for moisture, nutrient, and sunlight, and therefore become the target of both flea and weevil.
Conversely reducing the amount of nitrogen applied and lifting plant available calcium will bring about resurgence in the amount of clover in the sward. Clovers contain up to four times the calcium of rye grasses, just one of the reasons that animals grazing clover dominant pasture produce more and grow more rapidly than stock grazing other species.
Not only is extra calcium beneficial it is important that it becomes available to plants as they require it. This work is largely done by fungi, bacteria, and worms and the beneficial ones thrive in a calcium rich environment.
DoloZest, made by ESI using Golden bay Dolomite is available throughout the South Island. It contains both calcium and magnesium along with a wide range of selected soil friendly fungi and bacteria and has been applied over the last eight years to intensive dairy and grazing properties throughout both islands.
Measures from six properties from September to December in 2006 using DoloZest based nutrient programmes showed they contained twice as much clover compared to pasture from six properties using conventional nitrogen driven systems.
The percentage of the clover in the pasture from the conventional properties averaged 13% over the four months with 27% clover content in the pastures using DoloZest based programmes.
Not only is the clover content higher in properties applying DoloZest, but damage by clover flea and weevil is limited to such an extent that less than 20kgN/ha is required to grow in excess of 18 tonne of pasture in a twelve month period.