Conservation agriculture, Crop residues, Greengram, Herbicides, Weeds, Zero-tillage

Conservation agriculture (CA) based intensification of maize (Zea mays L.)-wheat (Triticum aestivum L. emend Fiori and Paol) system through inclusion of greengram (Vigna radiata L. Wilczek) during summer may improve productivity and promote sustainability. However, weeds are the major biotic constraint that limit productivity of short-duration greengram severely, if not controlled timely. Therefore, a field experiment was conducted during 2018-19 and 2019-20 to evaluate the residual effects of nitrogen (N) applied to the preceding crops, and the concurrent effects of tillage, residue and herbicide on weeds and greengram productivity and profitability under a maize-wheat-greengram cropping system. Four main plot treatments comprised of three zero-till (ZT) flat-bed with retention of residues (R) of greengram (in maize), maize (in wheat) and wheat (in greengram) and 50, 75 and 100% N of the recommended 150 and 120 kg N/ha applied to maize and wheat, respectively (~ZT+R+50N, ZT+R+75N, ZT+R+100N), and a conventional tillage (CT) with incorporation of these three crops residue and 100% of the recommended N to the preceding crops (~CT+R+100N). The sub-plot treatments were: ready-mix Na-acifluorfen (16.5%) + clodinafop-propargyl (8%) at 245 (165+80) g/ha applied post-emergence (PoE), pendimethalin at 1000 g/ha pre-emergence (PE) followed by (fb) imazethapyr at 75 g/ha PoE, pendimethalin at 1000 g/ha PE fb spot hand weeding (HW) at 25 days after sowing (DAS), and unweeded control (UWC). Results indicated that ZT with residue retention (ZT+R), irrespective of previous season N applications led to significant reduction in weed interference compared to CT+R+100N and gave better greengram plant growth, rhizobial symbiosis, yields and profitability over CT+R+100N. Among weed management treatments, sequential application of pendimethalin fb imazethapyr was comparable with ready-mix Na-acifluorfen + clodinafop-propargyl, but led to better weed suppression, and higher greengram growth, yields and net income. Thus, summer greengram in a CA based maize-wheat system with appropriate weed control employing herbicides may be a promising strategy for sustainable crop intensification in north-western Indo-Gangetic Plains of India.