Nutrient Dynamics in Grain Amaranth and Competing Weeds under Different Weed Management Practices

Abstract— A field experiment entitled "Effect of different post emergent herbicides on growth and yield of grain amaranth (Amaranthus caudatus L.)" was conducted at M block, field unit of AICRN on Potential Crops, University of Agricultural Sciences, Bengaluru during Kharif 2020. The experiment consisted of eight treatments which includes the application of five early post emergent herbicides (Fenoxaprop-p-ethyl, Quizalofop ethyl, Clomazone, Propaquizafop and Cyhalofop butyl), one manual weeding at 4 WAS, weed free check and weedy check which were replicated thrice in RCB design. Major weeds observed in the experimental plot were Cyperus rotundus, Cynodon dactylon, Echinochloa colona, Eleusine indica, Ageratum conyzoides, Alternanthera spinosa and Borreria articularis. Application of Quizalofop ethyl 5% EC at 50 g a.i. ha⁻¹ recorded significantly higher grain amaranth yield (1896 kg ha⁻¹), net returns (Rs. 68,178 ha⁻¹) and B:C ratio (2.56) which was on par with Propaquizafop 10% EC at 12 g a.i. ha⁻¹ (1805 kg ha⁻¹, Rs.63,524 ha⁻¹ and 2.38, respectively) without any phytotoxic effect on grain amaranth crop. However, weedy check recorded significantly lower grain yield (1005 kg ha⁻¹), lower net returns (Rs.25,731 ha⁻¹), lower B:C ratio (1.05) and higher weed index (51.29%) compared to other treatments. Similarly, nitrogen, phosphorus and potassium uptake by grain amaranth crop at harvest was significantly higher with early post emergent application of Quizalofop ethyl 5% EC at 50 g a.i. ha⁻¹ (74.1, 42.77 and 49.30 kg ha⁻¹, respectively) and lower in weedy check (30.44, 37.13 and 23.97 kg ha⁻¹, respectively).