Soil Thermal Response under Plastic Covers. I. Effect of Different Types of Films

An experiment was carried out during November 1996 at the Universidad Católica del Maule, Talca (35º26' S lat, 71º26' W long), in a Haplanthrept soil, to determine the soil's thermal response at 7 cm depth under four different plastic covers: transparent polyethylene (TRA), white/black film (OPA), brown AL-OR film (CAF) and orange polyethylene (NAR). TRA and OPA films were selected because of their opposite transmissibility, NAR and CAF films as plastic mulch options in the market. TRA achieved the highest temperature (mean maximal = 39.1°C), accumulating more heat than CAF. Both treatments produced thermal increases higher than OPA, which maintained the soil temperature slightly below that of the uncovered unit (mean maximal = 27.3°C), though this difference was not significant (Tukey 5%). The lower temperature accumulated by OPA, however, showed a compensation at night, with a higher minimum temperature than uncovered soil. CAF was not different from NAR, demonstrating that their advantages are not related to the thermal increase of the soil. According to the thermal rise of TRA, it would be possible to solarize at this latitude, obtaining possibly lethal maximum temperatures for mesothermal organisms after 15 days treatment in November, with 6 hours per day over 40°C. With the observed results, it is possible to conclude that the current utilization of plastic covers in Chile is deficient and, sometimes, contrary to the proposed objective. The information obtained is useful to verify a model that describes the thermal behavior of soil under a plastic cover. Durante noviembre de 1996 se realizó un experimento en la Universidad Católica del Maule, Talca (35º26' lat. Sur, 71º26' long. Oeste), en un suelo Haplanthrepts, para determinar la conducta térmica del suelo bajo cuatro cubiertas plásticas diferentes a 7 cm de profundidad: polietileno transparente (TRA), film blanco/negro (OPA), film AL-OR, café (CAF) y polietileno naranja (NAR). Se seleccionaron las láminas TRA y OPA por ser opuestas en transmisividad, NAR y CAF, como alternativas de acolchados (mulch) ofrecidas en el mercado. TRA alcanzó la temperatura más alta (máxima promedio = 39,1°C), acumulando más calor que CAF y produciendo ambos tratamientos incrementos térmicos superiores a OPA, que mantuvo el suelo ligeramente por debajo de la temperatura del suelo descubierto (máxima promedio = 27,3°C), aunque esta diferencia no resultó significativa (Tukey 5%). La menor temperatura acumulada por OPA mos