Effects of different fertilizing systems (chemical, biological and integrated) and irrigation regimes on the qualitative characteristics of forage and trigonelline content in fenugreek (Trigonella foenum- graecum L.)

The widespread use of chemical fertilizers and their effects on agricultural products is an issue that is still being studied and discussed. An important subject for study is the replacing of biofertilizers and organic fertilizers with chemical fertilizers and the application of integrated fertilizers to increase soil fertility in sustainable agriculture and for livestock (Wu, et al., 2005). Integrated fertilizing systems are more reliable than conventional fertilizers in producing better quality and higher quantities of whole forage in arid environments with water stress or a water deficit irrigation system. (Jahanian, 2012). On the other hand, drought stress is the most important abiotic factor that limits growth and development of plants in arid and semi-arid areas. Water stress conditions can also effect the root’s ability to uptake nutrients and leads to decreased forage quality. Evaluating new methods of irrigation and deficit irrigation systems can reduce the adverse effect of drought stress (Keshavarz Afshar et al. 2012). Therefore, the study of different fertilizing systems along with irrigation regimes is the main goal of this research in order to improve forage quality and trigonelline content in fenugreek plants.
A field experiment using a split plot on a RCB design with three replications was conducted at the Research Farm of the College of Agriculture, University of Tehran, in Karaj, Iran during the 2012 growing season. Treatments consisted of three levels of irrigation protocols assigned to the main plots as follows: complete irrigation (providing 100%), moderate drought stress (providing 75%) and severe drought stress (providing 50% of weekly evaporation). Six levels of fertilizing systems assigned to the subplots consisted of: a control, chemical fertilizer, biological fertilizer (seeds inoculated by Pseudomonas and Azotobacter), and three different integrated fertilizers: bio흍% chemical, bio% chemical and bio% chemical
By increasing the drought severity, the percentage of CP, WSC, NDF, ADF, ash and trigonelline concentrations increased while the percentage of DDM, mineral contents and trigonelline yield followed a decreasing trend. By increasing NDF and ADF, forage quality was reduced. This reduction also came with a decrease in DDM. Drought stress caused an increase in the trigonelline, while most of the growth parameters in the fenugreek plant decreased. The highest values for DDM, mineral contents and trigonelline yield were achieved with full irrigation treatment accompanied by integrated fertilizer (Bio75% and Bio50%). The highest percent of CP, WSC and trigonelline was measured in severe drought stress together with Bio100%.
The results of this experiment indicated that the integrated fertilizers were more efficient than bio- and chemical fertilizers. They could mitigate the adverse effect of drought stress and produced the highest forage quality and secondary metabolite. These characters along with less use of chemical fertilizers produced the highest yield in quality and quantity compared to the other fertilization systems. Under the conditions in Karaj, it seems that application of integrated fertilizers along with moderate deficit irrigation (providing 75% of weekly evaporation), due to less water consumption and less negative effect on yield and forage quality, can be suggested for a sustainable agricultural system in arid and semi-arid areas like Karaj, Iran. Fenugreek, due to its dual positive characteristics, can be suggested as a medicinal-forage crop for livestock