Variation of leaf characteristics with level of insertion on a grass tiller. I. Development rate, chemical composition and dry matter digestibility

The influence of leaf insertion level on the characteristics of blades and sheaths on primary tillers of a grass, Panicum maximum var. trichoglume, was examined for plants grown under controlled light, temperature and nutritional conditions. Leaves from insertion levels 3, 5, 7, 10 and 13 from the base of the tiller were harvested when first fully expanded and at 5, 10 and 20 days thereafter. The flag leaf (leaf 16) was harvested at full expansion only. Leaves of high insertion level developed more slowly, stayed green longer, and senesced more slowly than those of low insertion level. Leaf blades at the same stage of development showed a marked gradient in characteristics from low to high insertion level, the cell wall content increasing from 32.6 to 63.8%, the nitrogen concentration decreasing from 4.7 to 2.5%, and the dry matter digestibility decreasing from 77.3 to 65.0%. Overall, the percentage lignin tended to increase the higher the insertion level. Gradients for the sheath were generally similar to those of blades, but were less pronounced. The effects associated with insertion level reflected inherent ontogenetical changes in the structural characteristics of successive leaves. The changes may be important to potential forage quality, chemical composition, water relations of tissues, and the design of sampling technique. Nutrient status (e.g. critical values) may in some instances be better expressed on the basis of cell contents rather than dry matter.