Molybdenum status and its critical limits for french bean and cauliflower in acid soils of Himachal Pradesh
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Date
2023-07-11
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CSK HPKV, Palampur
Abstract
Molybdenum (Mo) an ultra-micronutrient plays key role in plants as an essential nutrient besides its
significance in regulating nitrogen availability. It is emerging as a deficient nutrient especially in acid soils. As in
Himachal Pradesh (HP), a significant area is under acid soils, likely to exhibit Mo deficiency. Since, no systematic
study has been conducted on Mo status and its critical limits in soils and plants for french bean and cauliflower.
Therefore, an investigation entitled "Molybdenum status and its critical limits for french bean and cauliflower in
acid soils of Himachal Pradesh" was conducted from 2019 to 2022. The study involved the random collection of a
total of 200 surface soil samples, analysed for soil pH, soil organic carbon (SOC) and available Mo through best
extractant. The average soil pH was found to be 5.86, indicating slight acidity, while the mean SOC was
determined to be 10.2 g kg-1
. Four extractants viz., Ammonium Oxalate (AO), EDTA, AB-DTPA, and Aqua Regia,
were compared to assess their efficiency in extracting Mo on 40 segregated samples based on pH and SOC (20
each). Among these, Aqua Regia extracted pseudo-total Mo, exhibited the highest extraction rate with an average
value of 0.41 mg kg-1
. Among rest of the three extractants, AO exhibited the highest extraction rate with an
average value of 0.120 mg kg-1
followed by EDTA and AB-DTPA. The effectiveness coefficients of the
extractants varied depending on the pH and SOC classes, with AO showing highest effectiveness at highest pH
(>6) and SOC (>10.0 g kg-1
) class. AO exhibited positive correlations with pH (0.334*), SOC (0.573**), N
(0.526**), and P (0.461**), indicating a significant association between AO and soil properties. Spatial mapping
of available Mo using the AO extraction method revealed a mean content of 0.122 mg kg-1
. The analysis indicated
that majority of the samples exhibited latent deficiency of Mo (43%), followed by low (28.5%) and very low
(6.5%).
To establish critical limits of molybdenum (Mo) in soil and crops, a controlled pot experiment was
conducted in a glasshouse. Ten different bulk soils (L1-L10) were selected, and six levels of Mo (0, 0.5, 1.0, 1.5,
2.0 and 2.5 mg kg-1
) were applied to study their impact on the growth and yield of french bean (var. Falguni) and
cauliflower (var. Pusa Snowball-K1). The experiment followed a completely randomized design with three
replications. The results indicated that for cauliflower, increasing Mo levels up to 2.5 mg kg-1 was statistically at
par with 2.0 mg kg-1
and resulted in improved growth parameters, yield attributes, yield, and nitrate reductase
activity (NRA). Similarly, for french bean, Mo levels up to 2.0 mg kg-1 which was statistically at par with 1.5 mg
kg 1
resulted in improved growth parameters, yield attributes, yield, and NRA. An increase in soil pH from 4.89 to
6.58 (L1-L5), and an increase in SOC from 2.90 to 15.1 g kg-1
(L6-L10), resulted in a significant and comparable
improvement in crop yield in the Mandi (L4) and Hamirpur (L9) locations, whereas Sujanpur (L6) demonstrated
the lowest performance with an SOC content of 2.90 g kg-1
. The post-harvest soil nutrient status showed that the
effect of Mo levels were non-significant for available N, K, Mg and DTPA extractable micronutrients. Among
locations, all the nutrients showed significant relationship. Critical limit for Mo in soil was worked out as 0.147
and 0.143 mg kg-1 for cauliflower and french bean, respectively. Critical limit of Mo for cauliflower and french
bean in plant was figured out as 4.12 and 6.16 mg kg-1
, respectively. In conclusion, the study provided valuable
insights into the distribution of available Mo in acid soils of Himachal Pradesh. The findings emphasized the
importance of Mo for crop production and the established critical limits shall serve as a useful guideline for
stakeholders.