Determination of Critical Limit of Zinc for Lentil (Lens culinaris L.) in Diverse Soils under Intensive Cropping Systems

Determination of the critical limit (CL) for nutritionally essential zinc (Zn) is very important in developing fertilizer recommendations for crops and soils. However, the CL of Zn for the lentil crop has not been determined yet in Bangladesh, leading to the use of a fertilizer rate for the crop estimated on the basis of old critical limit generalised for all crops. A study was conducted in the Greenhouse facilities of the Soil Science Division of BARI, Gazipur, from October to April (Rabi season) of 2018/2019 and 2019/2020, to determine Zinc CL for soils and lentil crop in soils collected at twenty locations encompassing the six Agro-Ecological Zones (AEZs) of Bangladesh. For extraction of available Zn concentrations from soils and lentil biomass, a diethylene triamine penta acetic acid (DTPA) (0.005 M) solution was used. The DTPA-extractable Zn (mg kg-1) in the soils were from 0.43 to 4.10 and from 0.52 to 4.20 in 2018/2019 and 2019/2020, respectively. In all seasons, accessible Zn had negative but substantial correlations with soil pH, soil P, Ca, and Mg in available forms, but the association between available Zn and lentil dry matter was positive and significant (DM). Soil Zn had also a positive significant correlation with Zn concentration of lentil tissue Zn (0.501**). In 2018-2019 and 2019-2020, the CL of EDTA-extractable Zn was determined to be 0.75 mg kg-1 and 0.68 mg kg-1 in soils for lentil crop (0.72 mg kg-1 on an average), respectively, while it was 48.6 mg kg-1 for lentil tissue. The revised CL can be used for fertilizer recommendation for the lentil crop in the entire Gangetic Plains and other Agro-Ecological Zones of Bangladesh. Keywords: Pulse crop, Nutrient management, Micronutrient, Dryland crop, Sustainable agriculture