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V. NAGARJUNA* AND D. MUTHUMANICKAM
Department of Soil Science and Agril. Chemistry, Tamil Nadu Agricultural University, Coimbatore, India
A mathematical model, based on the first order rate equation derived to determine the critical nutrient level in soil and plants. The model has been used to determine the critical level by characterizing plant growth as a function of nutrient concen-tration in plant tissues or content of the soil. A field experiments was conducted to establish critical limit to DTPA extractable Cu with graded levels of Cu (0, 0.5, 1.0, 1.5, 2.0, 2.5 and 3.0 kg Cu ha-1) as adopted during 2012-13 for onion growing soils in Tamil Nadu. The curve linear equation was developed based on the Bray’s percentage yield (Y) and soil available Cu (x). The extrapo-lated Bray’s per cent yield values at varying definite interval (0.1 mg kg-1) of DTPA extractable Cu in the soil were determined from the equation. The estimated Bray’s per cent yield was started to decline after the increasing the DTPA level of 3.00 mg kg-1 and upto this extrapolated Bray’s percentage yield was considered for estimation of ã. The critical concentration of available Cu in soil worked out to be 0.625 mg kg-1 below which appreciable responses to Cu application was expectable.
DTPA extractable Cu, Mitscherlich method, Onion growing soils, Onion leaf, Plant growth model.
Copper is an essential micronutrient for normal growth and metabolism of plants (Sharma and Agarwal 2005; Singh et al. 2007). Onion belongs to a group of vegetables that have high response to Cu (Swiader and Ware 2002). Micronutrient deficiencies become a major constraint for crop productivity in many Indian soils. The deficiency of micronutrients may either be primary, due to their low total contents or secondary, caused by soil factors that reduce their availability to plants (Sharma and Chaudhary 2007). Knowledge of micronutrient availability in the soil is fundamental for suitable fertilizer recommendations, to avoid deficiency or toxicity problems. Several studies have been conducted to determine the critical nutrient level in soils and plants. The critical levels have been determined by relating available nutrient content of the soil or nutrient concentration in the crop plant with yield. The critical limit in plant refers to a level at or below which plant either develops deficiency symptoms or causes statistically significant or 5 to 10 percent reduction in crop yield as compared to optimum (Debnath and Ghosh 2012).
Clear prediction of deficiencies, critical limits must be refined with reference to nutrient levels both in soil and plant. The suitable fertilizer recommendation can be
presented by calibration experiments with crop response results for each crop and determining of critical level of the element is necessary for particular crop (Soltanpour et al., 1986). Therefore, it is desirable to precisely know the critical limit of micronutrient in soil and plant is highly useful for providing suitable micronutrient application for crops. It reduces the concentration of micronutrients in soil solution below that required for normal growth. A modified Mistscherlich response equation to quantify critical deficiency levels by characterising plant growth as a function of tissue nutrient concentration (Ware et al., 1982). Critical level of Cu was reported as 1.3 mg kg-1 by Mistcherlich-Bray equation for obtaining 80 percent of maximum grain yield in wheat (Feiziasl et al., 2009). Sharma (1991) found that the critical N concentration of 3rd leaf from top of the potato for getting optimum tuber yield. Hence the present investigation was undertaken to study the response of onion to Cu fertilisation in the field conditions and to determination of critical limit the DTPA extractable Cu in soils
Field experiments were conducted at eight locations in various farmer fields at Vadivellampalayam, Panaiyampalli and Pungampalli villages in Tamil Nadu during Rabi season (2012-13) for refinement of Copper critical limit in soils.The soil of the experimental fields were belonging to the soil series Irugur, Manupatti, Vellalur, Palathurai, Athipalayam, Kanjampatti, Sommaiyanur, Puduvadavalli and Annur soil series (Table 1). The initial analysis of experimental soil was neutral to slightly alkaline in reaction and free from salts. The organic carbon content of the soil was low. The soil was low in available N and P, medium in available K, sufficient in DTPA extractable Zn, Mn, Fe and hot water soluble boron. Based on the available status of Cu, eight farm holdings (L1 to L8) were selected (on the ascending order of Cu status stating from 0.22 mg kg-1 at interval of 0.2 mg kg-1). The experiment was laid out in a randomised block design replicated thrice with seven levels of Cu application viz., 0, 0.5, 1.0, 1.5, 2.0, 2.5 and 3.0 kg ha-1 along with recommended fertiliser dosage 60:60:30 kg N, P2O5 and K2O kg ha-1 (Table 2). The fertilizers were applied in the form of urea, super phosphate and muriate of potash to all the treatments. Before sowing of onion bulbs, the required quantity of Cu was applied through CuSO4 as per the schedule. After harvesting of crop weight of bulbs was recorded separately and the collected soil samples were processed and analyzed for DTPA extractable copper with help of atomic absorption spectrophotometer.
A mathematical model, based on the first order rate equation was derived to determine the critical nutrient levels in soil and plants. The model has been used to determine nutrient levels by characterizing plant growth as a function of nutrient concentration in plants or nutrient available in soil or nutrient applied. The critical nutrient level can be determined by the equation
x = -In (0.1/Y) / K ,where
1-n 2.303 a a-y 0
K=∑ log10 n −1 and Y=
x a
k=1 a − y
where,
a = maximum estimated yield;
function of nutrient concentration in plant tissues or content of the soil. The model determines the critical soil nutrient level for which a large body of data is desired in order to get accurate critical values. The curve linear equation was developed based on the Bray’s percentage yield (Y) and soil available Cu status (x). The extrapolated Bray’s per cent yield values at varying definite interval of DTPA extractable Cu in the soil were determined from the equation.
Y = 34.07 + 14.39 x- 2.419 x2.
The extrapolated Bray’s per cent yield values at varying definite interval (0.1 mg kg-1) of DTPA extractable Cu in the soil was determined from the equation (Table 3).The estimated Bray’s per cent yield was start to decline after the increasing the DTPA level of 3.00 mg kg-1 and up to this the extrapolated Bray’s percentage yield was considered for estimation of γ, i.e. ratio of difference between maximum and minimum extrapolated yield divided by maximum yield.
γ = (55.50-34.07) / 55.50
γ = 0.3860
The average K value is 2.160.
Critical limit (x) = -In (0.1/γ) / K
x = 0.6253
The critical limit of DTPA extractable soil Cu value obtained from this study is 0.625 mg kg-1. Using the Mathematical method 0.625 mg kg-1 is the critical limit of DTPA extractable Cu in onion growing soils. Sharma (1991) reported the critical limit of 0.75 mg kg-1 DTPA-Zn for potato grown soil and also found that the critical N concentration of 3rd leaf from top of the Potato for getting optimum tuber yield. Similarly, Ware et al., (1982) used a modified Mitscherlich response equation to quantify critical deficiency levels characterizing plant growth as a function of tissue nutrient concentration.
y0 = minimum estimated yield (Sharma 1991).
A mathematical model, based on the first order rate equation derived to determine the critical nutrient level in soil and plants. The model has been used to determine the critical level by characterizing plant growth as a
A mathematical model, based on the first order rate equation derived to determine the critical nutrient level in soil and plants. The model has been used to determine the critical level by characterizing plant growth as a function of nutrient concentration in plant tissues or content of the soil. The curve linear equation was developed based on the Bray’s percentage yield (Y) and
soil available Cu (x). The extrapolated Bray’s per cent yield values at varying definite interval (0.1 mg kg-1) of DTPA extractable Cu in the soil were determined from the equation. The estimated Bray’s per cent yield was started to decline after the increasing the DTPA level of 3.00 mg kg-1 and upto this extrapolated Bray’s percentage yield was considered for estimation of ã. The critical concentration of available Cu in soil worked out to be 0.625 mg kg-1 below which appreciable responses to Cu application was expectable.
characteristics in lower shiwaliks of solan district in north –west Himalayas. Journal of the Soil Society of Soil Science. 55 (1): 40-44.
Sharma, R.K. and Agarwal, M. 2005. Biological effects of heavy metals: An overview. Journal of Environmental Biology. 26(2): 301-313.
Sharma, U. C. 1991. Response of soybean to micronutrients in acidic soils of Nagaland. Indian Journal of Hill Farm. 5(1): 75-76.
The author is highly grateful to the Indian council of agriculture research (ICAR), New Delhi and Tamil Nadu Agriculture University (TNAU) for providing financial assistance in the form of stipend during the course of this investigation.