Effect of Weed Free Periods and Crop Density on Morphological Traits, Yield, and Yield Components of Sesame (Sesamum indicum L.)

Oilseeds such as sesame (Sesamum indicum L.) are one of the rich sources of energy and protein that form the second most important food resource of the world after cereals. The factors like suitable plant density and weeds control are important for maximum economical yield. This crop is highly adapted to the climatic conditions of Iran and is highly tolerated to the drought. Therefore, the objective of the present study was to investigate the effect of weed free periods and plant density of sesame on yield, yield components and agronomic traits of sesame in Birjand, Iran.

The present study was carried out in research farm of Islamic Azad University of Birjand (Long. 59°13' E., Lat. 32°52' N., Alt. 1491m.). This experiment was performed as factorial based on Randomized Complete Blocks Design with three replications in 2013. Treatments were including weed free periods at five levels (weed free until 20, 40, and 60 days after sesame emergence, perfect weed interference and perfect weed free) and plant density at three levels (7, 14, and 28 plant m-2). In this research morphological traits, yield and yield components of sesame and dry weight and number of weeds per m2 were measured. The texture of the soil in research farm was clay loam with the pH of 7.24, electrical conductivity of 4.14 mmhos cm-1 and total N, P and K content was 0.038%, 7.21 and 223.5 ppm at the depth of 0-30 cm, respectively. Data were analyzed by SAS statistical software and means were compared by Duncan's Multiple Range test at 5% probability level.

Analysis of variance showed that yield and yield components traits were significantly influenced by plant density and weed free period. In addition, plant height, stem diameter, branches number of main stem, length capsule were significantly influenced by weed free period, but plant density affected only on plant height and first capsule height from the soil. The interaction between weed free period and sesame plant density was not significant on all traits except biological yield. Means comparison showed that increasing of weed free period had positive effect on morphological traits, yield and yield components of sesame, so that capsule number per m2 increased 3.98, 2.45 and 1.1 times, respectively in perfect weed free treatment compared to the treatments of the perfect weed interference and weed free until 20 and 40 days after sesame emergence. In addition, seed number per capsule increased 155, 20.2, and 9.8%, respectively and 1000-seed weight increased 20.3, 13.6, and 8.9%, respectively. The highest of seed yield (913.62 kg ha-1) belonged to the perfect weed free treatment that in comparison with treatments of perfect weed interference and weed free until 20, 40 and 60 days after sesame emergence had superiority of 15.5, 4, 1.8 and 1.3 times, respectively. Moreover, results indicated that in the perfect weed interference, weeds number per m2 had superiority of 22.6, 3.7 and 2.4 times, and weeds dry weight per m2 had superiority of 40, 8 and 2.8 times, respectively as compared with treatments of weed free until 60, 40 and 20 days after sesame emergence. These findings can be attributed to the increase in competition between crop plant and weeds for growth resources with prolonged weed growth. However, increasing the weed free period caused lower weeds emergence and growth and hence greater resources uptake by sesame plants that finally increased yield component and seed yield of sesame. Means comparison showed that the increase in plant density from 7 to 28 plants m-2 increased capsule number per m2 and seed yield by 76.4 and 72.79%, respectively and decreased weeds number and dry weight by 26.4 and 45.39%, respectively. It is seems that higher plant density per unit area caused maximum usage of production parameters and on the other hand, suitable density (28 plant m-2) increased the ability of crop competition  with weeds.

The results of this study showed that both weed interference and plant density, are the affecting factors on yield and yield components of sesame. The lowest yield was achieved at the highest level of weed interference and the lowest density of plants per square meter. High plant density is effective in crop yield due to reduced weed interference. Also, since the plant is susceptible to weed growth in the early stages, increasing the free weed period causes rapid plant growth and increases performance. According to the obtained results in this study, the best treatment for high yield production was perfect weed free and density of 28 plant per square meter.