Using Nitrogen to maximise summer milk production

Dry summers are a challenge for any South Island dairy farmer on non-irrigated land, and maintaining production through this period requires skilful management. The primary goals of summer management are to use all available pasture, achieve the maximum days in milk and protect next season's milk production.

A number of strategies can be used to achieve these goals, including: feeding extra supplements, growing summer crops and taking advantage of irrigation. Using timely, targeted applications of nitrogen before the moisture deficit becomes pronounced is proven to be a beneficial and cost-effective strategy. Results from field trials at DairyNZ revealed that nitrogen applications in early summer (December/January) stimulated tiller (shoot) growth from the base of ryegrass plants and discouraged seed head production. The application of nitrogen boosted shoot numbers by 37 per cent; less than half this response was achieved through the use of irrigation. The outcome of using nitrogen was higher quality pasture which maintained persistence and density through summer, and provided fewer opportunities for weeds to invade.

Another trial, conducted by John Penno, showed an extra 800kg DM/ha and 66kg MS/ha could be produced from December to April after 100kg N/ha was applied, split between December and January. The milksolids response came from extra days in milk – more cows in milk over summer and a later drying-off date - rather than an increase in daily milk production.

The More Summer Milk programme, carried out in the 1990s by DRC, was designed to demonstrate the effects of increasing summer feed supply. It compared cropping, silage and nitrogen use and looked at their effects on milksolids production and their financial returns. Cropping had drawbacks due to the removal of grazing area at the time of highest feed demand, as well as the costs of cultivation. Silage can be costly to purchase and proved to be less cost effective when compared to nitrogen. Nitrogen applications resulted in the most consistent and profi table response.

Secrets to success

Although applications of nitrogen can undoubtedly help to bridge the gap, a number of key factors need to be kept in mind:

To gain the maximum returns make sure you are able to utilise theextra feed eff ectively; this will ensure you gain the economic benefits of applying nitrogen and that pasture quality is maintained.

• Monitor pasture dry matter levels and turn the extra feed into supplement if it is not going to be eaten.
• Don't forget that a response will take 4 - 6 weeks after the nitrogen application to appear - factor this into your feed budget.
• Graze nitrogen-boosted pastures when they are at the same length as normal. You will get a greater dry matter response if they are spelled for longer, but this is likely to be off set by a loss in pasture quality, clover and new grass tillers.

The timing of applications is important.

• Make sure there is adequate soil moisture – this will minimise volatilisation losses (where nitrogen is lost to the atmosphere as ammonia gas), and ensure pasture plants are still actively growing and able to respond to the nitrogen boost. Ideally you want to apply nitrogen before rain or irrigation – you need more than 10mm of rain (or irrigated water) within a day of nitrogen application to ensure the nitrogen gets into the soil effectively.
• It is best to apply nitrogen when the pasture cover is between 1500 and 1800kg DM/ha (30 - 35 mm high). At these levels there is sufficient pasture leaf area for effective photosynthesis and thus for plant growth to occur.

Adjust nitrogen application rates depending on stocking rate. Forstocking rates at (or over) 2.5 cows/ha use two dressings of 30kg N/ha (two applications of 65kg n-rich urea/ha). For stocking rates below 2.5 cows/ha use two dressings of 20kg N/ha (two applications of 44kg n-rich urea/ha).

• Choose the right paddocks. High-fertility paddocks containing productive pasture species will give the best response.
• Monitor cow condition closely. Even with the extra feed provided you will need to dry off cows if their condition drops sufficiently.

Cutting edge technology

In typical pastoral situations, between 10% and 15% of the nitrogen applied as urea will be lost through volatilisation. However, in some situations losses may be nil; in others, as high as 50 per cent. Factors that increase the level of ammonia volatilisation are:

• The rate of nitrogen applied – the higher the rate, the greater the loss
• Soil moisture levels – the risk of losses is greater in dry conditions
• Soil cation exchange capacity – the lower the CEC, the greater the risk of loss
• Soil organic matter content – the risk of losses is greater when organic matter is lower
• Level of cover – lower crop or pasture cover is associated with higher losses of ammonia.

Most of the total ammonia loss occurs in the fi rst two to four days after application, and it's especially an issue if no rainfall occurs during this time.

With these considerations in mind, it is worth considering the use of SustaiN Green to boost your pasture or crops. Not only might this offer an economic benefit compared to using urea, it also gives flexibility when scheduling spreading contractors. SustaiN Green is a urea fertiliser coated with Agrotain™ a urease inhibitor that slows the conversion of urea to ammonium. This allows more time for the urea to move into the soil and decreases volatilisation losses.

The science around volatilisation is complex, and the outcomes can be affected by numerous factors, so talk to your Ballance or Farmlands representative to find out if SustaiN Green will suit your circumstances.

Article provided by Ballance Agri-Nutrients