G.K. Macleod

In situ organic matter degradability of untreated and urea-treated varieties of spring barley and oat straws, and of untreated varieties of winter wheat straws

Straws from 22 winter wheat, 14 spring barley and nine oat varieties were evaluated with the nylon bag technique to determine differences among cereal species in straw organic matter degradability (OMD) and OMD differences among varieties within species. Samples of 110 g each of the barley and oat straw varieties were sprayed with 25 ml of a solution of urea in water (16% urea, wt./vol.) to yield treated material containing 4 g of urea per 100 g straw dry matter (DM). Treated samples were stored in polyethylene bags for 6 weeks, at 21 °C after which their OMD values were compared with those of corresponding untreated straws. Average straw OMD values were different (P < 0.01) for winter wheat (35.7%), spring barley (48.7%) and oats (54.0%). Variability in OMD (mean/standard deviation) among varieties was highest for wheat straw (8.4%), followed by oat straw (5.7%) and barley straw (5.1%). There was no relationship between grain yield and straw OMD for wheat and oats. However, these two parameters were negatively correlated (P < 0.05) for barley. Shorter varieties of wheat and barley tended to have higher straw OMD values. Oat straw exhibited a greater response to urea treatment than barley straw (P < 0.001). The common slope for the regression lines (OMD treated v. OMD untreated) was less than unity (P < 0.01), indicating that varieties with low initial OMD values are upgraded to a greater extent than varieties with higher initial OMD values. These results indicate that it should be feasible to select varieties that may produce straw approaching the quality that would be obtained by chemical treatment of straw from low quality varieties. This strategy has important economic, biological and environmental implications, because it could reduce or eliminate the need for chemical or physical treatments.