Growth Analysis of Fenugreek (Trigonella foenum- graecum L.) under Various Levels of Nitrogen and Plant Density

Fenugreek (Trigonella foenum-graecum L.) is a specific condiment crop mostly grown for its edible parts, and is used as a green fodder and fresh vegetable. The seeds have medicinal value solely against digestive disorders, whereas its leaves are rich source of minerals and nutrients. The growth and yield of fenugreek is particularly affected by the application of nitrogen fertilizer and planting arrangement. Plant growth is a process of biomass accumulation which in turn is derived out of the interaction of the respiration, photosynthesis, water relations, long-distance transport, and mineral nutrition processes. Growth is the most important process in predicting plant reactions to environment. Irradiance, temperature, soil-water potential, nutrient supply and enhanced concentrations of atmospheric carbon dioxide are among some external components influencing crop growth and development. Growth analysis is a useful tool in studying the complex interactions between plant growth and the environment, clarifying and interpreting physiological responses. Plants total dry matter (TDM) production and accumulation can be appraised via relative growth rate (RGR) and crop growth rate (CGR) which are the most important growth indices. Leaf area index (LAI) is a factor of crop growth analysis that accounts for the potential of the crop to assimilate light energy and is a determinant component in understanding the function of many crop management practices.
A field investigation was conducted in a paddy field at Shaft County (Guilan Province) for eight consecutive months (from November 2009 to June 2010), to study the effect of four levels of nitrogen fertilizer (0, 25, 50 and 75 Kg N ha-1) and four levels of planting density (60, 80,100, and 120 plants m-2) on the growth indices of fenugreek (Trigonella foenum graecum L.) crop. The soil for the experiment was loam in texture and strongly acidic in reaction (pH 4.5). Sixteen treatment combinations, keeping nitrogen levels in main plots and levels of planting density in sub-plots, were replicated four times in a split-plot experiment on the basis of randomized complete block design (RCBD). Hand-sowing was done in lines (30 cm apart) as per experimental treatment. Weeds were controlled regularly during the whole study. All other recommend management practices were followed.Observations on leaf area and dry matter accumulation were recorded from all subplots (6 plants per subplot) with 15 day intervals up to crop maturity, initiating at 42 days after planting. Harvested plants were separated into remaining leaves, pods, and stems in the crown. The fresh weight of each sample was determined and the green leaf area of the remaining leaves was also measured immediately after harvest using a LI-3100 area meter (LI-COR, Lincoln, NB, USA). Shoot tissues were then oven-dried at 75°C for 24-48 h and dry weighs were calculated. STATGRAPH software was employed to find the best mathematical model to describe the relationship between total dry matter (TDM) accumulation, leaf area index (LAI), crop growth rate (CGR), relative growth rate (RGR) and growing degree-days (GDD).
Result indicated that the physiological indices were wholly influenced by applied treatments. The highest leaf area index was recorded in plots containing 120 plantsm-2 while receiving 50 kg pure N ha-1. Combined treatments of 120 plants m-2× 75 kg N ha-1 and 80 plants m-2× 50kg N ha-1 resulted in highest TDM and RGR rates, respectively. In all the applied interactions, among the podding and fully ripened pod stages, the CGR reached to its maximum rate (peak point) at around 1043 GDD from sowing and almost had a steady and linear trend which then slowly declined down turn to reach zero value at about 1400 GDD and thereafter to negative values. CGR was the highest in combined treatment of 120 plants m-2× 75 kg as compared to other nitrogen levels in this plant population.
Result showed that the physiological indices were all were affected by applied treatments. The highest leaf area index was recorded in plots containing 120 plants m-2 while receiving 50 kg N ha-1. Combined treatments of 120 plants m-2× 75 kg N ha-1 and 80 plants m-2× 50 kg N ha-1 resulted in highest DMW and CGR rates, respectively. RGR was the highest in combined treatment of 120 plantsm-2× 75 kg as compared to other nitrogen levels in this plant population after receiving 294.3 GDD.