Período de interferência de plantas espontâneas no estabelecimento da cultura da alfafa (Medicago sativa L.)

Abstract

Brazil is one of the largest producers of milk in the world, however, low production averages per cow and area are still observed. One of the reasons for these problems is the quality of forage available for feeding the herd. One of the alternatives to overcome this situation is the use of forage species of higher nutritional value, such as alfalfa (Medicago sativa L.), considered one of the best forages due to its high protein content. A problem in the production of quality alfalfa is the interference caused by competition with weeds, which possibly reduce the productivity of alfalfa. The experiment was conducted in a rural property in Laranjeiras do Sul/PR, from August 2015 to May 2016. The objective was to determine the necessary period of control of the weeds, characterizing the Period of Interference (PAI), Period Critical Interference Prevention (PCPI) and Total Period of Interference Prevention (PTPI). The experimental design was completely randomized blocks, with 16 treatments and 4 replicates. The treatments were composed of 8 culture periods with weeds (up to 7 DAS, 14 DAS, 28 DAS, 42 DAS, 56 DAS, 70 DAS, 84 DAS and 98 DAS) - and 8 periods without cohabitation with spontaneous plants - previous. The determination of the three periods was performed according to the relation between weeds and alfalfa productivity, accepting up to 5% losses on the maximum yield, through regression by the Boltzmann sigmoidal model. The accumulation of dry matter, stalk length, number of alfalfa branches and protein content were also evaluated, and the results were submitted to analysis of variance and significance. Comparing the results, the negative effect of alfalfa coexistence with spontaneous plants is evident, productivity at the end of the experiment shows that all alfalfa, submitted to different treatments were affected. The PAI was established until the 9th day after sowing and the PTPI until the 81st days after sowing, the interval between these two periods, being 72 days, the PCPI. The increase in the coexistence period caused a significant reduction in the accumulation of dry matter, number of stems, height and protein content of alfafa plants.