DELINEATION OF MANAGEMENT ZONES IN PASTURES ACCORDING TO NITROGEN RATE AND GROWING SEASON

Abstract

Soils for livestock production have a high heterogeneity that causes variability in forage
production. The aims of this study were (i) to assess the relationship between ECa and soil properties and then use this information to determine potential management zones (PMZ)
and (ii) evaluate if these PMZ are related to forage yield of tall fescue during different
regrowth periods under contrasting levels of N availability. The ECa was measured in a
5.75 ha paddock that sustained a permanent pasture dominated by tall fescue. A 30 m by
30 m grid cell size was chosen and 43 sampling areas (SA) each 4 m2 in size, were georeferenced.
In each SA soil samples were collected and analyzed for soil physicochemical
properties such as pH, texture, organic matter, gravimetric soil water content (%) at 33
and 1500 kPa, salinity, soluble sodium, calcium and magnesium and sodium adsorption
ratio . In addition, SA were divided into two experimental units of 1 m by 2 m, one of
which was fertilised with 250 kg N ha–1 (N250) at the beginning of four regrowth periods
(spring 2015, spring 2016, autumn 2016 and autumn 2017) and the other was not fertilised
with N (N0). At the end of each regrowth period, the accumulated biomass (AB) was
estimated. ECa was associated with salinity and sand percentage (R2 = 0,67). Two PMZ
were delimited and the differences in AB were compared through analysis of variance. In
spring, the average AB showed a significant PMZ x N interaction (P = 0.02). By contrast,
the effects of PMZ on forage yield were not statistically significant in autumn (P > 0.05). In
conclusion, in spring, the production of tall fescue can be managed by PMZs delimited by
ECa. However, the delimitation of PMZs was not possible during autumn.