Purple Nutsedge (Cyperus rotundus L.) Response to Type and Rate of Ammonium and Nitrate Sources as Nitrogen Fertilizer

Crop nutritional management is one of the most important components of integrated weed management which maintains crop yield and reduces weeds performance over time. Nitrogen fertilizer is one of the major factors that has a significant effect on plant growth characteristics so that an optimized growth and yield could be achievable by choosing an appropriate type and amount of nitrogen.
In order to study the effect of different types and rates of nitrogen fertilizer on growth characteristics of purple nutsedge (Cyperus rotundus L.), an experiment based on CRD (Completely Randomized Design) was conducted with three replications at the Research Greenhouse of University of Birjand in 2013. 12 different treatment levels consisting of calcium nitrate, ammonium sulphate and urea as well as nitrogen rates of these fertilizers (0, 50, 100, 200 mg N kg-1 soil) were used to conduct the research.
ANOVA results showed that nitrogen fertilizer treatments had a significant effect (P≤0.01) on all study traits of nutsedge. The results of this study showed that different growth characteristics of purple nutsedge responded differently to the nitrogen fertilizer treatments The greatest height of purple nutsedge (94 cm) was observed with 50 mg N kg-1 soil of ammonium sulfate source, which provided a 27.3% height increase compared to the control. The greatest stem number of weed was achieved with 50 mg N kg-1 soil of calcium nitrate, which provided a 37.50% increase in stem number compared to the control. Application of 50 mg N kg-1 soil of ammonium sulfate increased the weed leaf number by 62.37% compared to the control and showed the greatest value of this trait amongst all study treatments. Results showed that increasing urea consumption resulted in a significant increase in plant leaf area, so that using 50 mg N kg-1 soil of this source showed the highest leaf area, which accounted for 59.88% increase compared to the control. Increasing ammonium sulphate usage significantly increased the pre-tuber number, so that utilization of 50 mg N kg-1 of this fertilizer resulted in the highest pre-tuber number and 52.60% increase compared to the control. Application of ammonium sulphate and calcium nitrate fertilizers enhanced the tuber number, so that the maximum tuber number was obtained where 50 mg N kg-1 of these fertilizers were applied. Results showed that applying 50 mg N kg -1 soil of ammonium sulfate provided a 76.3% increase in tuber dry weight compared to the control, and the highest tuber dry weight (3.780 g plant-1) was observed with this treatment. Utilization of 100 mg N kg-1 soil of urea resulted in the highest rhizome dry weight (60.46% increase compared to the control). Moreover, the greatest shoot dry weight (9.729 g plant-1) and underground dry weight (4.634 g plant-1) was obtained with the usage of 50 mg N kg-1 soil of ammonium sulfate. On the other hand, the lowest height (62 cm), stems number (2.66 stem pot-1), leaf number (15 leaf pot-1), leaf area (2310.85 cm2 pot-1), shoot dry weight (1.014 g plant-1), pre-tuber number (2.33 pre-tuber pot-1), tuber number (4.33 tuber pot-1), tuber dry weight (0.218 g plant-1), rhizome dry weight (0.330 g plant-1) and underground dry weight (0.785 g plant-1) were obtained high rates (200 mg N kg-1 soil) of calcium nitrate and urea fertilizers were used.
Overall, the results showed that the application of ammonium sulfate and urea fertilizers at moderate rates (50 and 100 mg N kg-1 soil) can increase growth characteristics and competitive ability of purple nutsedge. It seems that farmers should consider these results and apply fertilizer types and rates resulting in the lowest growth where face purple nutsedge infestation. In this regard, the response of natural and horticultural crops competing with purple nutsedge should also be taken into consideration that will need further studies.