Report from NIAB

Drying matter analysis of Forage Maize

Introduction

The most important quality measure in forage maize National list is the dry matter content of a variety. The dry matter content characteristic is assessed by taking a 500g sub sample of fresh cut maize from each National List plot and drying the sample at 100degrees for 24hrs, which is enough time to ensure the crop is completely dry.

Recently the other aspects of crop performance, particularly the quality characteristics of whole plant digestibility and whole plant starch content have become more important to growers. These characteristics are routinely assessed for the purposes of the UK Descriptive List and current National list trials data on digestibility and starch content is included in Descriptive list data sets for these characters. This means that samples are taken from National list plots at the same time as the dry matter samples and analysed for starch and digestibility.

In Descriptive List trials the same 500g sample is used for assessing dry matter content, starch content and digestibility. However separate samples are still taken for dry matter content, then the other two characteristics are assessed from a separate sample. This means work repetition and an opportunity to cut costs by utilising one sample from the national list trial to cover analysis of starch content, digestibility and dry matter content.

However it is apparent that starch content and digestibility cannot be assessed from samples dried at 100degrees for 24hrs because at this temperature sugars are caramelised which effects digestibility and starch content analysis. For starch content and digestibility samples are dried at 60degrees for 48hrs which is sufficient time to allow samples to dry.

The scope of this study was to look at the feasibility of changing drying matter procedures to reduce cost and the potential effects of the altered methodology on variety ranking across the dry matter range from wettest to driest samples.

Methodology

Comparison were made between temperature and drying times for dry matter content assessments during the 2004 harvest season. Ten varieties were identified in National List 2 trials, which spanned the range of dry matter contents. Two representative 500g samples were taken from all three replicates of each variety of the Cambridge National 2 trial. These samples were weighed, and placed in two separate ovens one drying at 100degrees for 24hrs and one dried at 60 degrees for 48hrs. Samples were then taken from the oven and re-weighed. Dry matter contents were then calculated as a percentage.

Results

Results for 10 varieties indicated that in all cases varieties dried at 100degrees for 24hrs had lower dry matter content than those dried at 60degrees for 48hrs. On average this difference was 1.4% Dry matter content, but ranged from 0.7-1.9% (see table 1). This is a relative small difference and variation given the potential error associated with taking a sub-sample for dry matter analysis. It should also be noted that the lower dry matter in the 100degree samples would be expected for two reasons

1)higher temperature drive off a small amount of water that is not removed at 60degrees

2)It has been commonly suggested that caramelisation of sugars occurs at temperatures higher than 60degrees, with the effect that some sugar is burnt off hence sample weight is reduced and dry matters appear lower.

A further assessment of relative variety ranking indicates that ranking is almost totally unaffected by dry matter assessment method. With only one set of varieties changing place, this single variation in dry matter ranking lies well within the likely error that would be expected between varieties.

Conclusion

The results of work undertaken on the 10 variety, sub sample of NL2 was very positive. It is safe to assume from this work that variety ranking is unaffected by drying methodology. That drying at a lower temperature will increase dry matter content but this increase will have no effect on decision making as the increase in dry matter will be adjusted in standards by the control varieties.

In conclusion it is suggested that revising the current protocol for dry matter content to 60degrees drying over 48hrs would have no deletirious effect on variety decision making. This would also represent a cost reduction measure to be implement within the 2005/06 growing season.

Don PendergrastPage 110/06/2018

Report from NIAB

Don PendergrastPage 110/06/2018