impact of farmers' organic farming practices on soil properties in ...

2.4.3 Available potassium
FYM application to five successive crops increased the available soil K to the same
degree as K fertilizers did indicating that FYM was a good source <strong>of</strong> K which also had
favourable effect on K availability in soil (Grewal et al., 1981). Similarly, continuous manuring
with FYM over a period <strong>of</strong> 45 years in cotton-jowar rotation, increased the available potassium
significantly over unmanuring (Khiani and More, 1984).
Venugopal and Shivashankar (1989) reported that incorporation <strong>of</strong> maize straw @ 4
tonnes and @ 8 tonnes per ha released available potassium <strong>of</strong> 104 and 112 kg per ha,
respectively as compared to control (88 kg/ha).
Badanur et al. (1990) noticed that the available potassium content <strong>of</strong> soil was highest
in jowar stubbles incorporated plot (335 kg/ha) followed by safflower stalk and in both the
cases K was higher than green manured and RDF plots in Vertisols <strong>of</strong> Bijapur.
Application <strong>of</strong> vermicompost recorded significantly higher available potassium (10%)
as compared to fertilizers treatment alone (Phule, 1993) which was attributed to the rich K
content <strong>of</strong> vermicompost.
Balaji (1994) found higher levels <strong>of</strong> available potassium with either vermicompost
alone or in combination with FYM in Vertisols <strong>of</strong> Dharwad. The availability <strong>of</strong> potassium could
be improved by incorporation <strong>of</strong> cotton stalk @ 5 tonnes per ha in sunflower-bengalgram
cropping system (Quereshi et al., 1995).
More (1994) observed higher amount <strong>of</strong> available potassium where farmyard manure,
wheat straw, pressmud and biogas slurry were incorporated into the sodic Vertisol.
Application <strong>of</strong> vermicompost @ 5 tonnes per ha to maize crop resulted in significantly
higher available potassium content <strong>of</strong> soil compared to application <strong>of</strong> RDF alone in deep
Vertisols <strong>of</strong> Dharwad (Madegowda, 1997).
Mathur (1997) observed that application <strong>of</strong> 100 per cent <strong>of</strong> FYM significantly
increased available potassium over 50 per cent FYM + 50 per cent NPK. Increase in
potassium was due to reduction <strong>of</strong> K fixation in soil.
Increase in available potassium due to FYM and sunnhemp application was observed
by Bellakki and Badanur (1997) and it was attributed to direct addition <strong>of</strong> potassium to the
available pool <strong>of</strong> soil.
Incorporation <strong>of</strong> <strong>organic</strong>s viz., FYM, vermicompost and cotton stalk enhanced the soil
available potassium as compared to RDF alone (Patil, 1998 and Manjappa, 1999).
Nalatwadmath et al. (2003) reported a build up <strong>of</strong> available K only in <strong>organic</strong> manure
treatment which was maximum (33%) as compared to control.
2.4.4 Available sulphur
Immobilization <strong>of</strong> in<strong>organic</strong> form <strong>of</strong> sulphur occurs when low sulphur energy rich
<strong>organic</strong> materials are added to soils not plentifully supplied with in<strong>organic</strong> sulphur. The
mechanism is thought to be the same as that <strong>of</strong> for nitrogen. The energy rich material
stimulates microbial growth and the in<strong>organic</strong> sulphate is synthesized into microbial tissue.
Only when the microbial activity subsides does the in<strong>organic</strong> sulphate form again appear in
the soil solution. These facts suggest that like nitrogen, sulphur in the soil <strong>organic</strong> matter may
be associated with <strong>organic</strong> carbon in reasonably constant ratio (Williams, 1967).
Anandaswarup and Ghosh (1980) studied changes in water soluble sulphur as a
result <strong>of</strong> intensive cropping and manuring. They noticed that use <strong>of</strong> sulphur bearing source
i.e., superphosphate, resulted in the higher content <strong>of</strong> SO4-S in the soils, maximum being with
the use <strong>of</strong> FYM.
Kantharaju (1992) observed significant increase in available sulphur with
incorporation <strong>of</strong> crop residues. Highest increase was observed in treatment which received
maize residue with full dose <strong>of</strong> NPK fertilizer treatment followed by maize residue with half
NPK fertilizer treatment, maize residue alone and NPK fertilizer treatment alone.