EXTRACTION AND EFFICIENCY OF NUTRIENT USE BY PIATÃ GRASS IN RESPONSE TO THREE PRE-GRAZING HEIGHTS

Abstract

This work was carried out to evaluate the extraction, root mass, its colonization by mycorrhizal fungi, and the efficiency of nutrient use by Piatã grass managed under intermittent stocking with different pre-grazing heights. The treatments consisted of three pre-grazing heights, 30, 40, and 50 cm with four repetitions of sub-paddocks, totalizing 12 experimental units, in a completely randomized design, implemented in an area of 6.6 hectares (ha), which was divided into 12 sub-paddocks. The pre-grazing heights influenced air dry mass (ADM) and root system dry mass (RDM), with higher values for higher managed pastures, but pre-grazing height did not change the relationship between ADM and RDM, which are proportional. The RDM and the percentage of colonized roots presented mean values of 1.2 ±0.14 and 55%, respectively. Higher managed pastures increased the stem component, diluting the N and K contents of the forage, but due to the higher mass per grazing cycle, they occasionally extracted higher values of N = 127.1; P = 10.3 and K = 111.3 kg ha-1, which were counterbalanced by the lower number of grazing cycles, resulting in greater extraction of P and K throughout the growing season for 30 and 40 cm pre-grazing heights. The dry mass of roots is proportional to the dry mass of the aerial part of Piatã grass. Pre-grazing heights do not modify root colonization by mycorrhizal fungi. Only the levels of N and K in the forage of Piatã Grass are affected by pre-grazing heights. The variations in the dry mass of forage produced, modify the pattern of extraction of N, P, and K and the annual extraction of N in typical Orthic Quartzarenic Neosol.