Experimental Site and Soil Characteristics The experiment was conducted at high land of Breeder Seed Production Centre.
Cropping Season There are three cropping seasons in Bangladesh such as Rabi (mid-October to mid-March), Kharif-I (mid-March to the end of June) and Kharif-II (early July to mid-October). In Bangladesh, potato is cultivated only in winter season from November to February. The highest mean temperature in November was 24.2°C and 25.2°C in 2013 and 2014, respectively, where the coldest month was January. In January 2014, the lowest temperature was observed and it was 15°C. Between two seasons, February was dry where mean relative humidity was 84.9% and 86.8% in 2014 and 2015, respectively, with 19.3 mm rainfall in February 2014. In 2014-15, December and January were the most humid months with a relative humidity of 90.0 and 89.9%, respectively, including a sudden rain flash (38.7 mm) in January 2015. Rest of the months in both seasons was relatively dry.
Experimental Design, Treatment, Fertilizer Application and Intercultural Operation The experiment was laid out in a randomized complete block design (RCBD) with three replications. There were six treatments comprising different levels of zinc: T1 (0 ppm Zn), T2 (140 ppm Zn), T3 (280 ppm Zn), T4 (420 ppm Zn), T5 (560 ppm Zn) and T6 (700 ppm Zn). Fertilizers were used on soil test basis except zinc (Zn). Urea, TSP, MOP, gypsum, magnesium sulphate, zinc sulphate and boric acid were used as a source of N, P, K, S, Mg, Zn and B, respectively. All the fertilizers but half of urea was applied to the soil before planting tubers. Potato variety BARI Alu-25 (Asterix) was used as test crop. The unit plot size was 3 m × 3 m. Whole tubers of the potato were planted with a spacing of 60 cm × 25 cm on 15 and 17 November of 2013 and 2014, respectively. The irrigation was applied four times during the growing period. For proper germination, a light irrigation was applied at 7 days after planting (DAP) and second irrigation was done at 30 DAP after earthing up and side dressing of the rest urea. Rest two irrigations were done according to the demand of crops which was at 48 and 63 DAP. Zinc sulphate (ZnSO4) was applied at three stages of plant growth (stolonization, tuberization and bulking) followed by three foliar sprays. In each case of foliar spray, 2.25 L of ZnSO4 solution was applied at 9 m2 plot (2500 L ha-1). Weeding and mulching were performed as per requirement. Late blight disease was managed by spraying Dithane M45 at the rate of 2gL-1. After maturity, potato was harvested on 25 February 2014 and 30 February 2015, respectively.
Soil Sampling and Chemical Analysis Soil samples were collected, dried and ground for chemical analysis. Bulk density was determined by core sampler Method (Blake, 1965), soil pH was measured by glass electrode pH meter (1:2.5) and organic carbon by wet oxidation method. Total N content of soil was determined by Kjeldahl method, and available P (Bray-1 method), exchangeable K and available S contents by 0.5M NaHCO3 (pH 8.5), NH4OAc and CaCl2 extraction methods, respectively as outlined by Page, Miller and Kuny (1989). Available Zn content was determined following DTPA method.
Data Collection Data were taken on plant height, foliage coverage, stems / hill, tubers / hill, wt. of tubers / hill, tuber yield and tuber dry matter of potato. Tuber size and number were also recorded. Plant height, stem per hill and foliage coverage was assessed at 60 DAP using green method. The yield data were collected at harvest and dry weight was recorded at 7 days after harvest.
Storage Data The potato tubers were collected after harvest and weight of tubers were recorded. Weighing of tubers started from 30 DASt (days after storing) and continued at 15 days intervals up to 150 days. Rotten tubers were discarded after weighing.
Cost-Benefit Analysis The cost of chemical fertilizers, pesticides (inputs) and outputs (Tuber) were estimated as per prevailing market price. The gross return, net return and return per dollar invested in different nutrient management systems were assessed by computing the cost of the inputs and price of the produce/ output. Economic analysis was performed through partial budgeting followed by marginal benefit-cost ratio (MBCR) as suggested by International Maize and Wheat Improvement Center (CIMMYT) (1988).
Statistical Analysis The analysis of variance (ANOVA) for different crop parameters and dry matter was done following F test. When the F was significant at the p< 0.05 level, the means were separated by DMRT (Steel & Torrie, 1960) test. The SAS software (version 9.3) was used to analyze the data.