Effects of cow manure levels and plant densities on yield and seed yield components, leaf and indigo yields of true indigo

Introduction True indigo (Indigofera tinctoria L.) is a forgotten crop and medicinal plant from Fabaceae family. The plant is annual, biennial and perennial, but it is cultivated as an annual plant (6). A material called Indigo is extracted from the leaves of true indigo which is extensively used in industries for dying objects. It is blue in color. Indigo is formed when two indoxyl groups combine spontaneously in the presence of oxygen to form an indigo molecule (14).
Materials and methods In order to study the effects of cow manure and plant density on quantitative and qualitative criteria of true indigo as a forgotten and industrial crop, an experiment was conducted as factorial layout based on a randomized complete block design with three replications at the Agricultural Research Station, Ferdowsi University of Mashhad during two growing seasons of 2013-2014 and 2014-2015. Experimental treatments were five cow manure levels (10, 20, 30 and 40 t.ha-1) and four plant densities (10, 20, 30 and 40 plants.m-2). Studied traits were plant height, canopy diameter, yield components (such as number of branches per plant, number of pods per plant, number of seeds per plant and seed weight per plant), leaf yield, pod yield, stem yield, biological yield, indigo content and indigo yield of true indigo.
Results and discussion The results indicated that the effects of cow manure and plant density were significant (p≤0.01) on plant height, canopy diameter, number of branches per plant, number of pods per plant, number of seeds per plant, seed weight per plant, leaf yield, stem yield, pod yield, biological yield and indigo yield of true indigo. The highest canopy diameter was observed in 30 ton cow manure per ha (88.3 cm) and the lowest was shown for control (16.6 cm). The maximum canopy diameter was related to 30 plants.m-2 with 56 cm. The highest leaf yield was obtained in 30 ton cow manure per ha with 250.69 g.m-2. The maximum leaf yield was related to 30 plants.m-2 with 224.37 g.m-2. The highest indigo yield was achieved in 30 ton cow manure per ha (2.01 g.m-2) and by increasing plant density form 10 to 30 plants.m-2, indigo yield was enhanced up to 16%.
Conclusion By increasing cow manure application from zero to 30 t.ha-1 quantitative and qualitative yield of true indigo was enhanced. By enhancing plant density from 10 to 30 plants.m-2 growth, yield components, leaf yield, stem yield, pod yield and yield indigo of true indigo were improved.