Assessment of Soil Zinc Fractions and their Relationship with Physico-Chemical Properties of Rice Growing Soils of Boko Block of Kamrup(rural) District, Assam
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Date
2021
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Publisher
AAU, Jorhat
Abstract
A study on ‘Assessment of Soil Zinc Fractions and their Relationship
with Physico-Chemical Properties of Rice Growing Soils of Boko Block of
Kamrup(rural) District, Assam’ was conducted during 2019-2021 with the objectives to
assess different zinc fractions along with the physical and chemical properties of three
rice growing soils namely Ahu, Sali and Boro rice. The texture of the soils varied from
sandy loam to clay loam for Ahu and Sali rice while clay loam in Boro rice growing
soils with strongly acidic to moderately acidic in their reactions (pH 4.52 to 5.85). Soil
organic carbon was medium to high in Ahu and Sali rice but high in Boro rice growing
soils. All the available primary nutrients were medium in their status except available
phosphorus which was low to medium. Significant negative correlations were recorded
among soil pH, EC and SOC, and among sand, silt and clay fractions while significant
positive correlation was observed between SOC with CEC, available nitrogen, clay and
CEC with available nitrogen, potassium, exchangeable calcium, magnesium and clay
and available nitrogen with clay and exchangeable calcium with exchangeable
magnesium. The distribution of Zn-fractions followed a general order of dominance as
WSEX-Zn<CRYOX-Zn<COMP-Zn<AMOX-Zn<RES-Zn<TOT-Zn in all the rice
growing soils and was regulated by soil characteristics, dominantly, soil pH, CEC, soil
organic carbon and clay content in all the rice growing soils studied. The highest
amount of Zn was found in residual pool (~95%) and the lowest in water soluble plus
exchangeable fractions (~0.5%). The fraction WSEX-Zn, COMP-Zn, AMOX-Zn and
CRYOX-Zn was comparatively high in Boro rice while RES-Zn and TOT-Zn were
higher in Sali rice. Comparatively, high amount of DTPA extractable zinc was observed
in Boro rice growing soils (1.25 mg kg -1, mean) followed by Sali rice (1.08 mg kg -1)
and Ahu rice (1.01 mg kg -1). Overall contribution of DTPA-Zn was only 0.67% towards
total zinc in these soils. Soils under Ahu rice cultivation contained the lowest amount of
all the Zn fractions. All the Zn-fractions are significantly and negatively correlated with
soil pH and positively with SOC and clay. CEC was positively and significantly
correlated with WSEX-Zn, COMP-Zn and DTPA-Zn for all the rice growing soils.
Stepwise multiple regression indicated that in Ahu rice growing soils, SOC contributed
the highest variations towards WSEX-Zn (64.2%) fraction and COMP-Zn (44.9%)
while it was pH for AMOX-Zn (50.4%), clay content for CRYOXZn
(30.6%) and TOT-Zn (35.3%), SOC for RES-Zn (41.3%) and DTPA-Zn (28.4%).
For Sali rice, clay contributed maximum variation for WSEX-Zn (36.8%), RES-Zn
(37.2%) and TOT-Zn (39.0%) fractions, while maximum contribution was noticed in
CEC for COMP-Zn (39.4%), pH for AMOX-Zn (39.5%) and DTPA-Zn (31%),
available phosphorus for CRYOX-Zn (22.9%), respectively. In Boro rice growing soils,
CEC showed maximum contribution towards WSEX-Zn fraction (64.2%) while it was
SOC for rest of the fractions viz., COMP-Zn (56.8%), AMOX-Zn (53.0%), CRYOX-Zn
(51.1%), RES-Zn (54%), TOT-Zn (54.2%) and DTPA-Zn (35.4%) that contributed
maximum towards the variability of zinc. All the soil properties combinedly account for
30.6% to 78.1% variation for all the fractions in Ahu rice growing soils, 22.9% to 69.3%
in Sali rice and 51.1% to 87.5% in Boro rice growing soils. Among all the soil samples
studied (N=60) under Ahu, Sali and Boro rice growing areas, overall 58% of the
samples were found to be below critical level in DTPA extractable Zn and hence,
appropriate soil-zinc management strategies need to be adopted in those soils.