Phytoavailability of potassium to Zea mays L. grown in agricultural soils with

contrasting textures and mineralogy

M Faheem, I Bibi, NK Niazi, G Murtaza, U Riaz

Institute of Soil & Environmental Sciences, University of Agriculture Faisalabad

irshad.niazi81@gmail.com

15th International Congress of Soil Science, 2014 NARC, Islamabad

General Background

• Potassium (K) is an essential macronutrient in plants (10% of plant dry matter).• K is the most abundant major nutrient in soils. • Soil K content ranges from 0.01-4 % (average ~1%).• Two main sources of K in soils are:

a) Mica minerals (e.g. muscovite, biotite, illite)b) K-feldspars (e.g. orthoclase)

Chemical forms of K in Soil

Soil K is divided into four forms:• Water soluble K• Exchangeable K (adsorbed on the exchange sites of

SOM; and exchange, edge sites on clay minerals e.g. smectites)

• Non-exchangeable K (NEK) (from feldspars, interlayer sites of mica minerals)

• Structural K

Proportion of various chemical forms of K in soil

• Water soluble and exchangeable forms are the readily available forms (1-2% of total soil K).• NEK is in much larger content (90-99% of total K).• NEK largely dependent on amount and type of K

minerals• Interlayer K (ion exchange) has great significance

due to its reversible nature.

Potassium deficiency in Soils

In spite of its abundance, large agric. areas of the world are K deficient including:• 3/4 of the paddy soils of China;• 2/3 of the wheat belt of Southern Australia;• vermiculitic clay soils of Philippines• 30-35% of soils in Pakistan (e.g. district Kasur, soils

under potato-maize cultivation system)

Potassium deficiency in Soils

Potassium deficiency is a major limiting factor in • Sandy soils• Water-logged soils• Saline soils• Acidic soils• Intensive agricultural production systems,

particularly coarse textured or organic soils

Factors affecting soil K

The fate of applied K depends on:• Soil texture• Clay content - soils with high clay content can

release 35-70 kg K ha-1 a-1.• Clay mineralogy (e.g. Vermiculite, biedellite

dominated soils have high K fixing capacity)• Crops grown (e.g. cotton and maize require more K

compared to other crops)

Objectives

• To investigate the effect of K application on growth of maize grown in two soils with contrasting textures and mineralogy.• To delineate the dynamics of various soil K pools in

contrasting soils.

Materials and Methods

Glasshouse experiment

Soil types: 2• Soil per pot: 5 kg• Crop: maize• Potassium levels: 4 (0,

30, 60, 90 mg K per kg soil)• Potassium source: KCl• Replications: 3

Soil K analyses

• Water soluble K – water extraction method• Exchangeable K – ammonium acetate extraction

method• Non-exchangeable K – sodium tetraphenyl borate

method• Total K – nitric acid digestion methodSoil mineralogy• X-ray diffraction (XRD)

Cox and Joern, (1997); Darunsontaya et al., (2012)

Plant analysis

Plants were harvested after 14 weeks• Plant height, dry biomass recorded• Plant parts were digested• Potassium in plant digests was analysed using

flame photometer

Miller, (1998)

Results

Physico-chemical properties of soils

Properties Textural Class

EC dS m-1

pH CEC(cmolc kg-1)

Clay (%)

Water Soluble K (mg/kg)

Exchangeable K (mg/kg)

Non- exchangeable K (mg/kg)

Total K (mg/kg)

Soil I Sandy Loam

0.17 8.1 7.1 22 22.50 72.21 591.04 1267.07

Soil II Clay Loam 0.34 8.4 13.1 36 48.76 (54%)

206.74 (65%) 865.74 (32%) 3955.72 (68 %)

Effect of K on plant height and dry matter yield

0

20

40

60

80

100

120

0 30 60 90

Plan

t hei

ght

(cm

)

Potassium rate (mg/kg)

Soil I Soil II

0

3

6

9

12

15

0 30 60 90Sh

oot d

ry w

eigh

t (g)

Potassium rate (mg/kg)

Soil I Soil II

Potassium concentration in maize plant shoot

10000

15000

20000

25000

30000

35000

0 30 60 90

Shoo

t K c

onc.

(mg/

kg D

W)

Potassium rate (mg/kg)

Soil I Soil II

Water soluble and exchangeable K in post-harvest soils

0

10

20

30

40

0 30 60 90

Wat

er s

olub

le K

(mg/

kg)

Potassium rate (mg/kg)

Soil I Soil II

0

50

100

150

200

0 30 60 90

Exch

ange

able

K (m

g/kg

)Potassium rate (mg/kg)

Soil I Soil II

Non-exchangeable and total K in post-harvest soils

0

500

1000

1500

2000

2500

3000

0 30 60 90

Non-

exch

ange

able

K (m

g/kg

)

Potassium rate (mg/kg)

Soil I Soil II

0

2000

4000

6000

8000

10000

12000

0 30 60 90

Tota

l soi

l K (m

g/kg

)Potassium rate (mg/kg)

Soil I Soil II

Photo showing the difference in maize plant biomass in two contrasting texture soils

K-30 mg/kg K-60 mg/kg

Soil I Soil II Soil IISoil I

Conclusions• The dry matter yield of maize was 2 fold higher in Soil I

compared to Soil II.• Plant shoot K concentration was (2 times) higher in Soil

I than Soil II• Exchangeable K pool in Soil II (clay loam) was more

than 2-folds greater than in Soil I (sandy loam).• The NE-K fraction significantly decreased at 60 and 90

mg/kg K levels in Soil I, probably due to the release of K from NE-K to the water soluble soil K for plant uptake.• The results show that increased phytoavailability of K in

Soil I (sandy loam) compared to Soil II (clay loam) led to better yield of maize crop.

Acknowledgements

• We acknowledge the Higher Education Commission (HEC) of Pakistan for financial support.• All the laboratory staff at Soil and Water Chemistry

laboratory.