Monday, 15 February 2021

Getting the best response from N


Between 2013 and 2018, around 25% of dairy farms used more than an average 190kg N/ha with even greater proportions of dairy farmers in Canterbury and Southland exceeding this amount. Dr Ants Roberts discusses some options for getting the best responses out of nitrogen (N) fertiliser ahead of the 190kg N/ha ‘N-Cap’ due to come into effect on 1 July 2021.

In the quest for increased productivity, a proportion of farm systems have been set up with a permanent mismatch between feed supply and demand which has been met, in part, with systematic N applications after nearly every grazing. For some farmers, meeting N-loss targets and N fertiliser caps will require a considerable reduction in the reliance on N fertiliser to supply critical feed throughout lactation. Fortunately, there are several levers available to farmers which can be implemented in a variety of combinations to suit farmers’ own personal circumstances, with the ultimate goal of farming with less N fertiliser inputs.

Optimising pasture production without N fertiliser

Ensure pasture production is not limited by:

a. Soil fertility - soil and herbage testing required for both major and trace elements
b. Drainage - where possible drain perennially wet areas
c. Compaction - check the soil for signs of compaction and subsoil or aerate as required.

Encourage clover to thrive in your pasture by ensuring:

a. Good establishment practices (don’t sow too deep)
b. Good grazing management (don’t let grasses shade out clovers).

Maximising the response to N fertiliser at each application

Get the best out of the reduced N fertiliser used by:

a. Using N fertiliser tactically by predicting the deficit between feed supply and demand, not by regular application every round
b. Cutting N application rate per dressing from 1kg N/day-in-round to 0.8kg N/ha
c. Applying N when residual herbage mass is between 1300-1800kg DM/ ha
d. Allowing 23-28 days for pasture to respond to N fertiliser (see grazing round 3.b)
e. Reducing or avoiding applications (summer) as soil temperatures exceed 16°C
f. Use urease-inhibited urea products (N-Protect) and use 3-5kg N/ha less each application
g. Using proof of placement maps to record form, time, rate and placement of fertiliser each application (keep a running total per hectare across the season).

Farm system ‘tweaks’ to match feed supply and demand

Changes to farm systems may be required, for example:

a. Calve later (e.g. 7-10 days later) to better match pasture growth increases
b. Graze at at the 2.5-3 leaf stage (23 to 25-day rotation length in spring/summer) to reduce the number of grazing rounds and, if following
cows with N, this may also reduce the number of applications
c. Use a mixture of diploid and tetraploid grasses in your pasture to help maintain quality on a longer round. Tetraploids are also more compatible with clovers
d. Start to cull low-performing cows early (e.g. first cut in February)
e. Pre-graze mow to increase intake
f. Post-graze mow to maintain pasture quality
g. Carefully consider any additional supplements
h. Dry the herd off earlier.

Other environmental considerations

General advice to reduce the overall environmental impacts of N fertiliser use include:

a. Applying less N fertiliser on effluent paddocks (utilise the N from the effluent)
b. Excluding high fertility areas (especially dung and urine transfer areas) like around troughs, near gateways
c. Managing irrigation to avoid drainage and N loss
d. Reducing or avoiding areas that are dry or consist of poor pasture species.