Friday, March 29, 2024

Taking the holistic view

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Dairy farmers looking for ways to reduce their nitrogen leaching should analyse the impact on their whole farm system before making changes, DairyNZ farm systems specialist Chris Glassey says.
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He told Massey University’s Fertilizer and Lime Research Centre’s annual workshop in late February changing one component without considering the farming system as a whole could have detrimental effects on both environmental and financial bottom lines.

“Our motivation for this paper was our observation that some of the recommendations that are being made to farmers about reducing nitrogen leaching on their farms are incomplete,” he said.

“They are often based on some generalisations that in themselves are absolutely correct but lack analysis at a farms systems level on their impact on both nitrogen leaching and farm profit.”

Glassey used the introduction of maize silage as an example.

“Maize silage has many useful attributes that we can use in this whole area of reducing nitrogen leaching.

“An example of a generalisation about maize silage that I extracted out of a publication that goes in front of farmers – feeding maize silage, a relatively low crude protein feed, reduces the amount of nitrogen in urine and can greatly reduce leaching losses.”

Glassey cited farmlet trials conducted by DairyNZ that compared various levels of maize silage supplementation with a base system that did not feed silage.

“We added in extra cows to allow for the extra feed we added in – we’re adding nitrogen all the time. Despite the fact that you can get some efficiency gains in milksolids produced per kilogram of nitrogen as you go this way you still get an increase in nitrogen leaching.”

He said a differentiation was needed between system change and system optimisation.

“If we look at system optimisation, yes it is possible that nitrogen loss will decrease if we’re in the systems optimisation space – that’s if total nitrogen inputs are reduced or we capture some efficiency gains there without increasing the nitrogen surplus.

“Reducing urinary nitrogen concentration is a desirable thing to do but we’ve got to remember that that is only if the number of urine patches on the farm is not greatly increased.”

Glassey said there are effectively three options to reduce a farm’s nitrogen surplus: reduce nitrogen inputs, convert more nitrogen into product, and intercept and capture a proportion of the nitrogen surplus excretion then redistribute at a time when there is less risk of nitrogen leaching.

Stocking rate is one avenue that is available for reducing a farm’s nitrogen surplus.

Referring to a DairyNZ-run trial comparing farm profitability at various comparative stocking rates (CSR) kg liveweight (LWT)/ha rather than cows/ha, Glassey said the CSR where profit is maximised on a farm (75-80kg LW/ha) is well below where milk production is maximised.

His DairyNZ colleague, productivity developer Sean McCarthy, suggested CSR could also stand for “comparative stress rate”.

“When a farm is under high stress, it tends to drive the nitrogen input up because people try and compensate,” Glassey said.

“Check the CSR, find the cows contributing little to profit but probably adding quite a lot to the catchment’s nitrogen surplus.”

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