Delimitación de zonas de manejo en pasturas bajo diferentes niveles de nitrogeno y epocas del año

espanolLos suelos ganaderos presentan una elevada heterogeneidad que provoca variabilidad en la produccion de forraje. Por lo tanto, los objetivos de este trabajo fueron (a) determinar, a escala de lote, si la relacion entre la conductividad electrica aparente (CEa) y propiedades edaficas, permite delimitar zonas de manejo potenciales (ZMP) y (b) evaluar si estas ZMP se relacionan, en primavera y otono, con la variacion espacial de la produccion de forraje de una pastura de festuca alta creciendo con y sin limitantes de nitrogeno (N). En un lote de 5,75 ha que tenia implantada una pastura de festuca alta, se midio la CEa y en una grilla de 30 x 30 m se georreferenciaron 43 areas de muestreo (AM) donde se determinaron propiedades edaficas (pH, textura, materia orgânica, humedad gravimetrica (%) a 33 y 1500 kPa, salinidad, sodio, calcio, magnesio solubles y relacion de absorcion de sodio). Ademas, en cuatro rebrotes: primavera 2015, primavera 2016, otono 2016 y otono 2017 se marcaron dos parcelas en cada AM y se aplicaron dos tratamientos: N0 (sin aplicacion de N) y N250 (250 kg ha-1 de N) para determinar la biomasa seca acumulada (BA). La salinidad y el porcentaje de arena fueron las variables que mas explicaron la variabilidad de la CEa (R2 = 0,67). Para el lote bajo estudio se delimitaron dos ZMP hallandose, en la BA promedio de primavera, interaccion entre los factores de tratamiento ZMP y N (P = 0,02). Sin embargo, este comportamiento no se manifesto en la BA promedio de otono (P > 0,05). En conclusion, mediante la CEa podrian delimitarse ZMP en primavera lo que facilitaria el manejo de pasturas de festuca alta. En cambio, no seria posible delimitar ambientes en otono. EnglishSoils 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.