A greenhouse experiment was carried out with Brachiaria brizantha (Hochst ex A.Rich) Stapf. cv. Marandu to study the effects of potassium rates in dry matter yield, plant tillering, potassium concentration and distribution in sampled parts of shoots. Ground quartz was used as substrate in pots. Eight potassium rates (0; 9.75; 39; 78; 156; 234; 312 and 468 mg K L-1) were used and the experiment was set in a randomized complete block design, with four replications. Plants were first harvested 38 days after transplanting the seedlings to the pots and the second harvest 33 days after the first one. In each harvest, plant tops were separated into: non-expanded leaves, laminae of the two newly expanded leaves, laminae of the other expanded leaves and culms plus sheaths. After the second harvest, roots were collected. Forage yield, plant tillering and potassium concentration in each sampled part were increased with potassium rates in the substrate. Maximum forage yield was reached at potassium rates of 365 and 399 mg L-1 and the highest tiller number ocurred at rates of 312 and 468 mg L-1. A second-order model fitted to the potassium concentration in the non-expanded leaves picked up in the two harvests and also in the other sampled parts in the first harvest. For the expanded (newly or other) leaves or culms and sheaths in the second harvest, the data for potassium concentration fitted to a first-order model. The amount of potassium in the culms and sheaths exceeded that of any other part sampled in the shoot of this forage. The use of young leaf blades for potassium diagnosis in this forage is recommended. Critical potassium levels in this plant tissue were between 22 and 29 g kg-1.
potassium; Brachiaria brizantha cv. Marandu; dry matter yield; plant tillering; plant parts
