Effects of Soil Texture and Burial Depth on Biological Characteristics of Purple Nutsege (Cyerus rotundus L.)

Cyerus rotundus is a perennial weed of the Cyperaceae family spread throughout the tropical and subtropical parts of the world. It is a C4 and fast-growing plant that replicates rapidly through the extensive underground system and tuber. This weed causes damage to more than 92 countries and 50 crop species. In this regard, it is considered as the most damaging weed in the world. The amount of damage varies depending on the crop. One of the most important characteristics of purple nutsedge is the production of the tuber. According to available studies, burial depth of tuber plays an important role in the emergence of the onset of the competition period. Among the physical properties of the soil, soil texture plays an important role on plant growth characteristics, development of underground organs, especially in tuber plants and the amount of water penetration and maintenance. So, given the importance of accurately recognizing the biology and the ability to reproduce of nutsedge in its management, this research is also intended to study the effect of burial depths and the soil texture on the growth of purple nutsedge.

In order to evaluate the effects of soil texture and burial depth on purple nutsedge vegetative characteristics, a trial was conducted at Kerman Natural Resources and Agricultural Research Center, using factorial statistical method and experimental design of randomized complete blocks at three replications. The first factor was burial depth at five levels (2, 12, 22, 32 and 42 cm) and second factor was soil texture at three levels (sandy loam, silty loam and clay loam). The traits of emergence percentage, the time of emergence, the number of produced tubers and dry weight of the underground organs were measured at 130 days after planting. For this purpose, the pots and dumps were emptied, then the underground organs were separated and placed in paper envelopes and finally, paper envelopes were placed in oven with temperature of 75°C for 72 hours. Data were analyzed using SAS v. 9.1 software. Figures are also plotted by Sigmaplot v. 12 and Excel v. 2013.
Results and Discussion The results showed that emergence time, germination percentage, underground organ dry weight and tuber numbers were affected by depth of planting and soil texture. Emergence of C. rotundus was faster in sandy soil and at a lower depth, so that the tubers grew in the sandy loam soil at a depth of 2 cm 7/7 days after planting (the shortest time), and silty loam and clay loam were ranked next lowest. Understanding ecology of germination and weed emergence plays an important role in their management. With increasing depth of sowing, the percentage of germination in the tested soil texture decreased. So that the maximum amount of germination (85%) was obtained at 2 cm depth of sandy loam soil and the lowest germination percentage was observed at depths > 32 cm in silty loam and clay loam soils and the depth of 42 cm of sandy loam soil encountered with no germination and emergence of seedling. According to the results, the underground organ dry weight of C. rotundus in the textures and depths of the soil was quite different. In sandy loam, the highest underground dry weight was obtained at the 2 cm depth and the lowest was at 42 cm depth (0) of sandy loam. The highest underground dry weight of the tuber (63.6 g) was observed at 12 cm depth and the lowest (0) was obtained at 32 and 42 cm depths. The results showed the highest tubers number was observed at 2 cm depth of sandy loam soil and the lowest was obtained at 42 cm depth of sandy loamy and 32 cm and 42 cm depth of sandy loamy. The number of tubers decreased with increasing planting depth in all three texture types. The highest percentage of tuber production in heavy textures (silty loam and clay loam) was formed in layers of 2 to 12 cm of the soil.

The results showed that with increasing depth in all three types of soil texture, all the growth characteristics of purple nutsedge significantly reduced. More than 80% of the distribution and dispresal of underground organs was formed at a depth of 2 to 12 cm. The percentage of emergence decreased by 100 % at 32 and 42 cm depths of clay loam and silty loam. It seems that, the lack of emergence at the high soil depth is due to disruption of gas exchanges and lack of light. Given the importance of tubers in reproduction of this plant, this should be considered in management strategies. The deep plowing by delaying the emergence and growth and decreasing the production of reproductive organs (rhizome and tuber) of purple nutsedge can be considered as a management option. This weed has high emergence ability in the sandy loam soils due to high permeability and porosity.