Diversity and Evenness of Weeds in Forage Corn Field under Different Tillage Systems

Introduction: Weed control is the most important challenge for adoption of conservation tillage systems. Tillage prepares optimum conditions for growth and development of crops. Conservation tillage compared with conventional tillage has many advantages in terms of improving soil conditions and soil moisture retention. Nevertheless, during the preparation of seed bed, decreasing of soil disturbance in different conservation tillage methods could be resulted in optimal conditions for growth of various weeds. Although each of the conservation tillage methods affect on weed population dynamics and change weed density and diversity, the effects of tillage systems on weed dynamics and diversity depend upon species, location and environment which is complex and not fully understood. Materials and Methods: To investigate the effect of different tillage systems (Conventional, Minimum tillage and No-tillage) on diversity and evenness of weeds at beginning and end of critical weed control period in forage corn field, a study was conducted in a Nested design in Azadshahr during 2013 growing season. The experiment consisted of three methods including no-tillage, reduced tillage (once or twice a composite disk tillage) and conventional tillage (moldboard plowing once and three times the disk). The experiment was done in three separate plots and the size of each plot was 1500 m2. 15 samples were selected in each plot using a 1*1 m2 quadrate and number of weeds species were counted, separately in each plot. Fifteen kg. ha-1 seeds of corn cultivar SC 770 was planted at 01/07/2013 for all tillage systems. Row spacing and distance of seeds on rows considered as 75 and 14 cm, respectively and seeds were buried in 4-5 cm in all studied tillage systems. 15 samples were selected in each plot using a 1*1 m2 quadrate and number of weeds species were counted, separately in each plot at begging and end of critical weed control period (CWCP).Data Analyses To calculate Simpson's diversity index we've used relation 1 (10): (1) In above relation: 1-D: Simpson's diversity index; ni: number of people at ith variant; nj: number of people at jth variant; N: Number of all people; S: Number of all variants, at sample has been showed. To calculate Camargo uniformity index we've used relation 2 (10): (2) In this relation: E': Camargo uniformity index; ni: number of people at ith variant; nj: number of people at jth variant; N: Number of all people; S: Number of all variants, at sample has been showed. To calculate Rencon Similarity index we've used relation 3 (22): (3) In this relation: P: percentage of samples 1 and 2 similarity; p1i: percentage of "i" variant exist at sample community number1; p2i: percentage of "j" variant exist at sample community number2. Drawing of all regressions in these studies, calculation of uniformity index, similarity index has been made by Excel. SAS software has been used to fit regressions. Results and Discussion: Simpson diversity index (SDI) at the beginning of the critical period for no-tillage system Determined as 0.30 whichwas less than SDI of the other two tillage systems. However, at the end of CWCP, amount of SDI for conventional tillage system (0.40) was less than minimum and no-tillage. Camargo uniformity index was determine 0.16 and 0.24, 0.16 and 0.20, 0.20 respectively at beginning and end of CWCP for no-tillage, conventional and minimum tillage systems, respectively. Results revealed that weeds at the end of CWCP and in no-tillage system have more evenness than other two tillage systems. The results showed that at least two of tillage and conventional tillage, for the beginning and end of the critical period of weed diversity, there was little difference. But no-tillage system at the critical period of weed diversity was lower than the critical period.The results showed that at least two of tillage and conventional tillage, for the beginning and end of the critical period of weed diversity, there was little difference.But no-tillage system at the critical period of weed diversity was lower than the critical period.Alsothe minimum value for the no-tillage system and obtained weed diversity at the beginning of the critical period.The highest diversity of weeds for no-tillage system at the end of the critical period.Similarity index showed thatgrown species at the beginning of the season until the end of the critical period, growth was sustained in the field but no-tillage system as much similarity in the beginning and end of the critical period was only 35 percent; this suggests that the species composition of weeds in no-tillage system is dynamic in time. Conclusion: Thanks to my wife on the cheek counting and measurement of dry weight species helped me