Efeitos da geada em canola (Brassica napus L.) em função da distribuição da palha na superfície do solo

Abstract

Canola is a winter crop that has good adaptability to low air temperature, but depending on environmental conditions and developmental stage the occurrence of frosts can cause significant damage to the crop. However, few studies characterizing environmental and micrometeorological variables linked to frost and relating them to the plant response to cold. This study aimed to determine the canola answers to frost due to the straw distribution on the soil surface in the beginning of the crop development cycle. Field experiment was conducted in 2014 with three sowing dates, sown from April to July and four types of delivery straw on the soil surface: soil without straw on the surface (SSP), ground completely covered with straw (CT), soil with waste from other crops (CS) and without straw sowing line (LSP), It used a randomized block design. Evaluations were performed at dawn with the occurrence of frost, when it analyzed the following variables: net radiation, leaf temperature, air temperature, surface temperature, and mortality phenological variables plants and plant fenometric. In general, the net radiation in the treatment CT was less negative, especially on nights with frost occurrence of moderate to strong, which was also found to lower surface temperature measurement infrared thermometer. Meanwhile, the LSP treatment met the balance more negative radiation from the treatments and the surface temperature in LSP was similar to the SSP treatments and CS. In addition, the CT treatment was observed at lower air temperature than 3 cm above the soil, which was reflected in the lower temperature of the sheet measured with thermocouples and infrared thermometer. Thus on 19/06 average temperature of the rosette plant in CT was -0,66 ºC and 0,42 ºC in LSP. While the temperature of the leaves in 14/08 was -3,62 ºC in CT treatment and -2,88 ºC in LSP treatment. As a result, the TC treatment plant mortality was 30% in 19/06 and 14/08 32,75%, while in LSP treatment mortality of plants was 0% and 1,25% for the respective dates. Therefore, removal of the seeding line straw can be an alternative to reduce the negative effects of frost canola plants early in the development.