27 July 2001

Whole-crop study aims to pinpoint best harvest date

By Marianne Curtis

PREDICTING whole-crop yield and nutrition at different growth stages is the objective of a new SAC monitoring scheme.

The trial, which begins this week at SACs Boghall Farm, south of Edinburgh, will follow crops of winter barley, winter wheat, spring barley and spring wheat for five weeks until harvest. Measurements will include grain texture, yield and dry matter for both the head and straw portion of the crop, says SAC adviser George Barton.

"There is conflicting advice on the optimum growth stage for harvesting whole-crop. These trials should provide information on when the crop should be harvested to maximise energy content."

Crop characteristics will be described each week, to give an indication of how growth stages are identified in the study, funded by FSL Bells as part of its HarvestMORE initiative. Descrip-tions for this weeks report (below) were made on July 19.

The head and third bottom leaf from winter barley was turning yellow, while leaves of other crops remained green. Individual grains were well formed in all crops except spring wheat.

Removing the outer husk and squashing grains between the forefinger and thumb was used to assess grain texture. As expected, winter barley was most advanced with grain texture similar to a medium dough (table 1). Winter wheat and spring barley were similar, both being at the soft cheese stage, although wheat was slightly behind barley. Grains in spring wheat were only just forming.

Straw height was measured from the ground to where it joined the head (table 2). Height of straw is important, allowing eventual feed value of harvesting heads with varying proportions of straw to be estimated.

Plants were cut at 3cm (1.2in) from the ground and then straw and head separated. These were dried to obtain a dry matter yield. Head yield includes all sections of the head; grain, chaff and awns, which would be fed if the crop was cut with a forage harvester.

While fresh weight yields are interesting, DM yields tell the true nutritional value of the crop. DM of the head varied considerably bet-ween winter barley and other crops, however, straw DM was similar.

The head yield in winter barley was greater than straw yield, while for the other crops the opposite applied. Total DM yield of winter barley and winter wheat was similar, but with a much higher proportion of green leaf and longer growing season, we would expect both wheat crops and spring barley to continue growing.

&#8226 Further information on the HarvestMORE initiative, focusing on maximising feed value from home-grown cereals and proteins, is available from FSL Bells (0800-374325, fax 01249-700751). &#42

Table 1. Description of whole-crop heads on July 19


Winter barley Winter wheat Spring barley Spring wheat

Growth stage 85 75 75 71

Grain texture Medium dough Soft cheese Soft cheese Watery ripe

Colour of head Yellow/green Green Green Green

Fresh yield (t/ha) 17.3 13.3 9.4 4.2

% dry matter 52 31 33 28

Yield dry matter (t/ha) 9 4 3.1 1.2

% of crop (DM) 66 30 33 26

Table 2. Description of whole-crop straw on July 19


Winter barley Winter wheat Spring barley Spring wheat

Colour Green Green Green Green

Height cm 84 74 73 65

Fresh yield (t/ha) 18.7 33.2 27.5 14

% Dry matter 25 29 23 25

Yield dry matter (t/ha) 4.7 9.6 6.4 3.5