The Effect of Cutting off the Wild Barley (Hordeum spontaneum C. Koch) Spike in Wheat on Its Population in Chickpea under a Crop Rotation System

Transient and persistence of weed seed banks impact on weed population dynamics. Therefore, any management tools with having a reducing role can affect weed population size. Reduction of weed seed rain using effective control tools can reduce weed density. The seed bank density is the main factor corresponding to seedling density. Decline of seed bank is critical to success in crop production, so that,   poor performance in weed control only for a season cause to rain weed seeds and to improve soil seed bank. Most of the commonly used herbicides recommended for controlling weeds in wheat fields are not efficiently able to control the wild barley (Hordeum spontaneum C. Koch). Hence, utilizing appropriate agronomic strategies to control this weed is critical. Evaluation the effect of wild barley spike cut-off in the previous wheat field, and the effects of chickpea planting date and chemical weed control in chickpea cultivation in rotation on wild barley weed population in chickpea cultivation are among the aims of this study.

The effect of wild barley spike cut-off in the previous wheat field, and sowing date and management strategies in chickpea on its population in chickpea for the following years was evaluated in Khorramabad, Lorestan, Iran during 2009-10 and 2010-11 growing seasons. The experiment was arranged in a factorial split plot in a completely randomized block design with three replications.  The wild barley spike cut-off in wheat (at two levels: No cut-off and with cut-off) and chickpea planting date in the next season (at two levels: early planting and late planting) were assigned into the main plots. Chickpea weed management treatments (at five levels: pre emergence application of metribuzin at 0.7 kg per hectare, pre emergence application of imazethapyr 0.7 litter per hectare, post emergence application of Clethodim 1 liter per hectare, weed free treatment, and weedy infest)was assigned into the sub plots.

Wild barley spike cut-off in previous wheat reduced 71% of the density and biomass of this weed in chickpea cultivation in the following years. This suggests the importance of recent year's wild barley seeding rain in the completion of the soil seed bank for the next season. Early planting of chickpea compared to late planting decreased the wild barley density by 75%. It was mainly related to the ineffectiveness of planting operations in full control of the large wild barley plants in the late planting treatment. Early planting of chickpea under wild barley weed spike cut-off in previous wheat crop condition, was completely free of wild barley. Accordingly, the prevention of wild barley seed rain and the completion of the soil seed bank in the previous year, along with the timely planting of chickpea led to full control of this weed. Triple interaction effects of experiment factors on wild barley biomass in chickpea was statistically significant. This suggests the difference of wild barley biomass response to weed management treatments in different planting date of chickpea in spike cut-off and without spike cut-off of wild barley in the previous wheat crop. In addition to manual weeding treatments in different conditions, all weed management practices, even uncontrolled weedy check, in early chickpea planting under spike cut-off of wild barley conditions in wheat cultivation in the previous year, did not emerged any wild barley seedling. This indicates the high efficiency of spike cut-off of wild barley in the previous year and the prevention of seeding and the timely planting of chickpeas in the management of this weed.

Thus, it seems that the major part of the growing population of this weed is dependent on previous year seed rain. In the other words, the wild barley population dynamics is largely dependent on the temporary transient seed bank instead of a persistent seed bank. This suggests the possibility of managing problematic wild barley and reducing its population below the economic damage threshold through prevention of seed rain and soil seed bank management.