Managing Nitrogen Applications in Multi-Cut Grass Systems

The three key principles of good silage making are dry matter, sugar and reducing buffering capacity.

Fig1. Changes in PH of crops of low and high buffering capacity in first 10days of ensilement (Wilkinson,2005).

“The aim of ensilement is to achieve a stable forage between 3.8-4 PH”

Multicut silages are an excellent way to provide more high-quality grass silage over a season. There are other factors including PH and sulphur that grass needs but the key requirements are water, sunlight, warmth and nitrogen.

Multicut silage is cut between 4/5weeks after the 1st cut and this continues through the season. A Hybrid (Italian + perennial) rye grass ley requires 2units/1kg/acre of Nitrogen (N) per day. If we cut silage in 30 days time, we will require 30kg of N/acre/day. It is important not to oversupply Nitrogen for reasons outlined below. If we used standard Nitram (34.5% N/tonne) we would require 87kg/acre of Nitram application.

By oversupplying N, we increase the “buffering” capacity of the grass silage meaning that N interferes with acidification and damages fermentation. PH thus fails to fall to sufficient levels leading to secondary fermentation (see figure 2), energy loss and protein damage (i.e. amines).

Fig2. Typical changes in PH during primary and secondary fermentations (Wilkinson, 2005).

Excess N encourages leaf growth and reduces Water Soluble Carbohydrates (WSC) build up in the stem, which is crucial for good fermentation leading to higher grass nitrates in silage. These nitrates cause weak salts in the fresh crop to uncouple as acidification increases rather than holding together. These uncoupled acids combine with acids of fermentation and end desired fermentation prematurely and so fail to reduce PH to desired levels.

The aim is to provide 30 grams/kg of WSC (WSC) per kilogram of fresh weight for good silage fermentation. Tedding within two hours of mowing helps achieve this, concentrates sugars, it also helps remove some of excess N if present. Given that multi cut silage is smaller tonnage/acre, care must be taken not to over wilt, particularly during 2nd and 3rd cuts (24 hour wilt is likely to be too long in this situation).

A red clover/perennial rye grass ley will become self sufficient in N supply, especially later in the season, although it will need an application before first cut. Slurry and manure reduce fertiliser costs and utilise farm waste however, they do contain undesirable microorganisms which interfere with silage fermentation and ideally should be avoided in a multi cut system however, reducing applications and slurry injecting is a common compromise.

For forage planning, please contact Wesley – wesleyhabershon@fcgagric.com or your local FCG Office.

Posted in Arable & Crops, Business Management, Chippenham.