Zinc requirement of green gram (Vigna radiata)–wheat (Triticum aestivum) crop sequence in alluvial soil

A field experiment was conducted during 2008–10 at Bichpuri, Agra on a zinc-deficient soil, to assess the direct and residual effect of different levels of applied Zn on yield of green gram [Vigna radiata (L.) Wilczek] and wheat [Triticum aestivum (L.) emend. Fiori & Paol.] and uptake of nutrients by the crops and soil fertility under greengram–wheat crop sequence. The experiment was laid out in randomized block design with 5 levels of zinc (0, 2.5, 5.0, 7.5 and 10.0 kg/ha) with 4 replications. An application of 5 kg Zn/ha to greengram recorded significantly highest plant height (53.5 cm), pods/plant (35.8), seeds/pod (12.8) and 1,000-grain weight (32.04 g). Zinc fertilization in preceding greengram crop at 7.5 kg was found to be best for growth and yield attributes of wheat. Green gram crop responded significantly up to 5 kg Zn/ha by producing 1,052 kg grain and 1,816 kg straw/ha. The residual effect in wheat crop was significant at 7.5 kg Zn/ha and grain and straw yield increments were to the extent of 15.3 and 12.4% respectively. The content and yield of protein in both the crops increased significantly with an increase level of zinc. The uptake of Zn by both the crops increased significantly by increasing levels of zinc. A phenomenal increase in N and K uptake, except of P and S, was recorded in greengram and wheat crop due to increasing levels of zinc up to 5 and 7.5 kg/ha respectively. DTPA-extractable Zn was reduced in the control plot after harvesting of wheat. At higher levels of Zn, sufficient DTPA-extractable Zn (0.80 mg/kg) remained in the soil after growing 2 crops and further crops could be taken without the application of Zn. The values of efficiency indices decreased with the increase in levels of zinc. Net returns and benefit: cost ratio were the highest with 5 kg Zn/ha in the greengram-–wheat crop sequence.