Efeitos De Níveis E Épocas De Desfolhamento Sobre O Rendimento E Os Componentes Do Rendimento De Grãos Da Soja

Abstract

RESUMOO objetivo do trabalho foi de avaliar o efeito de níveis e épocas de desfolhamento sobre o rendimento de grãos e componentes do rendimento da soja, em semeadura direta. O experimento foi conduzido na Estação Experimental Agronômica da UFRGS, na safra 2002/03. O delineamento experimental utilizado foi o de blocos ao acaso com parcelas sub-subdivididas e quatro repetições. Os tratamentos foram desfolhamento em quatro estádios de desenvolvimento (V9 -nono nó, R2 -floração, R5 -início enchimento do grão, R6 -máximo volume de grãos), dois níveis de desfolhamento (33 e 100 %) e testemunha, sem desfolhamento. A cultivar utilizada foi CEP/CD 41, precoce, determinada. A redução do espaçamento entre fileiras de 40 para 20 cm, aumenta o rendimento de grãos mesmo com o desfolhamento. A redução no rendimento, em R2 e R5, foi maior quando as plantas foram totalmente desfolhadas. O estádio mais crítico para perda de área foliar é o R5, decrescendo o rendimento à medida que se intensifica a remoção da área foliar da planta. O componente do rendimento com maior redução, em função do desfolhamento, foi o número de legumes por m 2, , particularmente com 100% de desfolhamento no início do enchimento de grãos.Palavras-chave: Glycine Max (L.) Merrill, estádio de desenvolvimento, remoção de área foliar, rendimento. ABSTRACTThe objective of this research was to evaluate the effect of levels and growth stage of defoliation intensity and timing on grain yield and yield components of no-till soybean. The experiment was performed at the Estação Experimental Agronômica da UFRGS, in the growing season 2002/2003. The experimental desin was a randomized complete block, with sub-subplots, and four replications. The treatments were defoliation at three development stages (V9 -nine node; R 2 -flowering; R5 -begining of seed fill; R6 -maximum seed volume), two defoliation levels (33 and 100%) two row spacing and a check, without leaf removal. The short season CEP/CD 41 cultivar was used. Row spacing reduction from 40 to 20 cm increase grain yield even with defoliation. Yield reduction in R2 and R5, was greater with total defoliation. The most critical stage for leaf area removal was R5, the yield reduction increasing with the intensification of defoliation. The yield component with most reduction with defoliation was pods per m 2 , particularly with 100% defoliation at the begining of seed filling.

Agronomic performance of soybean according to stages of development and levels of defoliation

“…Ribeiro and Costa (2000) also observed drastic reductions in yield with defoliations greater than 67% at all the developmental stages evaluated, and yields were even weaker if defoliations were applied in the reproductive stages of development. Likewise, in similar trials, Fontoura et al (2006) observed that the treatment with 100% defoliation in the R 5 stage led to the lowest grain yield, with reduction of 76% in relation to the control.…”

“…However, there are some practices suggested in the literature for the purpose of lessening the damages. According to Costa and Daros (2006), reduction in the spacing between plant rows may decrease the effects caused by defoliation. From the results, it is possible to see that the cultivar BRS Favorita ® exhibits sensitivity to defoliation, with alteration in all the traits evaluated, except for plant height.…”

Defoliation percentage in two soybean cultivars at different growth stages

“…Peterson et al (1998) verified that defoliation lower than 50%, before flowering, usually does not decrease grain yield, while in the reproductive stages, it has caused higher reductions in the production. Also, Fontoura et al (2006) report that defoliations lower than 67% did not affect the grain yield of the cultivar 'BR 16' , regardless of the stage.…”

Defoliation at different vegetative stages and assessment of morphological and yield components

“…Similarly, Diogo et al (1997), observed a tendency to increase the productivity with defoliation of 33 and 66%, mainly in the V3 stage. Reichert and Costa (2003) assessed that up to 33% defoliation in the vegetative stages resulted in no change in yield, in the same way, and Fontoura et al (2006) found that there was no significant effect of defoliation in vegetative period on the grain yield, but only assessed the stage V9 within the growing season. Similarly, Peluzio et al (2004) demonstrated that defoliation of 33% in all growth stages and up to 66% by the V5 results in no effect on productivity, results similar to those found in this work, where defoliation from V4 to V9 provided increases in productivity culture in relation to the control treatment.…”

“…Regarding the percentage of defoliation, research has established levels for the control of insect pests, when the defoliation are greater than 30% in the vegetative phase, or 15% in the reproductive ph ase. However, these recommendations are based on work done in the 70-80's decades (Fontoura et al, 2006). In this sense, another key issue for reduction of income is the degree to which defoliation reduces light interception by the canopy (Higley, 1992).…”