Experimental site and initial soil status:
A field experiment was conducted at On Farm Research Division, Rangpur during Kharif 1 season in 2020. The study area was under the agro-ecological zone Tista Meander Floodplain Soil (AEZ-3). The experimental field was a piece of well-drained medium high land. The soil type was sandy loam in texture; having low organic matter content. Initial soil samples were collected from a depth of 0-15 cm and analyzed prior to application of different fertilizers are presented in Table 1. The initial soil analysis was an indicative of B deficiency in the experimental field. The critical level of boron with reference to crops in general was reported to a range from 0.3 to 0.8 ppm depending on soil types (Shorrocks, 1984).
Treatments and fertilizers:
Five treatments having three replications were used for mungbean production. Treatments were built up by using five levels of boron (0, 0.5, 1, 1.5 and 2 kg ha-1). The design of the experiment was randomized complete block design (RCBD). A basal application was made with 9 kg ha-1 N, 18 kg ha-1 P, 24 kg ha-1 K and 12 kg ha-1 S, 2 kg ha-1 Zn and 0.08 kg ha-1 Mo in each plot to support normal plant growth. The entire amount of P from TSP, K from MOP, S from gypsum and half of N from urea, Zn from zinc sulfate heptahydrate and Mo from ammonium molybdate were applied during final land preparation. Rest of the N from urea was top dressed after 20 days of sowing.
Experimental work:
The unit plot size was 2m x 3 m and seeds of BARI mung 8 were sown at 16 march, 2020. The soils of all plots were kept moist to confirm sufficient moisture with addition of light water for quick germination. Irrigation was given according to need throughout the period to keep the soil moist. Necessary intercultural operations were done throughout the cropping season for proper growth and development of the plant. Mungbean were started to harvest at 7 May, 2020. Ten plants were taken from each plot to measure the yield attributes. Seeds were dried in an oven at 70°C for 72 hours and the dried samples were then finely ground in a grinder for laboratory analysis. After harvest, the soil from each plot was thoroughly mixed and approximately 100 g soil was sampled for laboratory analysis.
Methods of analysis:
For initial soil analysis, soil pH was measured by a combined glass calomel electrode (Jackson, 1958). Organic carbon determination was done by wet oxidation method (Walkley and Black, 1934). Total N was determined by modified Kjeldahl method. Elements K, Ca and Mg were determined by NH4OAC extractable method and Cu, Fe, Mn and Zn were determined by DTPA extraction method followed by AAS reading. Boron was determined by CaCl2 extraction method. Phosphorus was determined by Bray and Kurtz method while S by turbidimetric method with BaCl2.
Boron uptake and its use efficiency:
Boron uptake was determined by the following formula:
B uptake (kg ha-1) = B % × Dry weight (kg ha-1) /100
Agronomic efficiency, (AE) = (SYNA-SYNO)/ NRN (FRG, 2018)
Where, AE = Agronomic efficiency
SYNA = Seed yield (kg ha-1) with addition of nutrient
SYNO = Seed yield (kg ha-1) without addition of nutrient
NRN = Rate of added nutrient (kg ha-1)
Recovery efficiency was calculated by the following formula:
Recovery efficiency, (RE) = (NUNA-NUNO)/ NRN (FRG, 2018)
Where, RE = Recovery efficiency
NUNA = Nutrient uptake due to nutrient addition
NUNO = Nutrient uptake due to nutrient omission
NRN = Rate of nutrient addition