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

farmer under kharif jowar (10.90%), R 2 farmer under rabi jowar (10.20%), S 3 farmer under
sugarcane (11.70%) and V3 farmer under vineyards, which could be ascribed longer duration
<strong>of</strong> <strong>organic</strong> <strong>farming</strong> practice and larger quantity <strong>of</strong> <strong>organic</strong>s added to the soil by those farmers
(Table 1).
5.4 EFFECT OF ORGANIC FARMING ON AVAILABILITY OF
PLANT NUTRIENTS IN SOIL
5.4.1 Available nitrogen
The data on available nitrogen (N) content <strong>of</strong> soil (Table 14) indicated that its values
were higher in soils under <strong>organic</strong> <strong>farming</strong> than conventional <strong>farming</strong>, irrespective <strong>of</strong> cropping
system followed. Production <strong>of</strong> appreciable quantities <strong>of</strong> carbonic acids during decomposition
<strong>of</strong> <strong>organic</strong> matter mineralize the complex <strong>organic</strong> substances, which in turn would contribute
to N pool. An increase in available N by application <strong>of</strong> vermicompost and FYM was reported
by Phule (1993), Balaji (1994) and Pawar (1996). The increase in available nitrogen due to
<strong>organic</strong> matter application is also attributable to the greater multiplication <strong>of</strong> soil microbes
caused by the addition <strong>of</strong> <strong>organic</strong> materials which mineralize <strong>organic</strong>ally bound N to in<strong>organic</strong>
form (Bellakki and Badanur, 1997).
In cotton based cropping system, among the soils <strong>of</strong> four <strong>organic</strong> farms, the highest
increase <strong>of</strong> 21.90 per cent in available nitrogen content was observed in soils <strong>of</strong> C4 farmer,
which might be due to addition <strong>of</strong> higher quantities <strong>of</strong> nitrogen added to the soil through
<strong>organic</strong>s i.e., 162.60 kg N per ha per year (Table 3).
Among the soils from jowar cropping systems, the highest increase in available N
content was observed in soils <strong>of</strong> R1 farmer (15.12%). Addition <strong>of</strong> higher quantities <strong>of</strong> nitrogen
through <strong>organic</strong>s (123.90 kg N/ha/year) was responsible for build up <strong>of</strong> available nitrogen in
soil.
In sugarcane based cropping system, the highest increase in available N content was
recorded in soils <strong>of</strong> S3 farmer (19.82%), which could be ascribed to the addition <strong>of</strong> 147.90 kg
N per ha per year through <strong>organic</strong>s and more number <strong>of</strong> years <strong>of</strong> <strong>organic</strong> <strong>farming</strong> practice (10
years).
In vineyard system, the highest increase in available N content due to <strong>organic</strong> <strong>farming</strong>
was recorded in soils <strong>of</strong> V3 farmer (12.95%), which is attributable to the addition <strong>of</strong> higher
quantities <strong>of</strong> nitrogen (150.80 kg N/ha/year) to the soil through <strong>organic</strong>s.
5.4.2 Available phosphorus
The results <strong>of</strong> available phosphorus content <strong>of</strong> surface and sub-surface soils
indicated that it increased under <strong>organic</strong> <strong>farming</strong> in all the cropping systems compared to
conventional <strong>farming</strong> (Table 15). Singh et al. (1982) noticed an increase in available
phosphorus content <strong>of</strong> soil due to incorporation <strong>of</strong> FYM alone or in combination with in<strong>organic</strong>
fertilizers and attributed it to the enhanced solubilization <strong>of</strong> native phosphorus and added
phosphorus by the decomposition product <strong>of</strong> <strong>organic</strong> manures. Venkateshwarulu (1983)
noticed an increase in available phosphorus with the application <strong>of</strong> <strong>organic</strong> residues over a
period <strong>of</strong> five years in red soils <strong>of</strong> Hyderabad. Tandon (1987) attributed the increase in
available phosphorus with FYM application to the contribution <strong>of</strong> P by the <strong>organic</strong>s to the soil
available pool and coating <strong>of</strong> <strong>organic</strong> material on sesquioxides which reduces the phosphate
fixing capacity <strong>of</strong> soil. Similar observations were also reported by Bharadwaj and Omanwar
(1994).
Under cotton based cropping system, the highest increase <strong>of</strong> 19.60 per cent in
phosphorus content due to <strong>organic</strong> <strong>farming</strong> was recorded in soils <strong>of</strong> C4 farmer, which might be
due to addition <strong>of</strong> higher quantities <strong>of</strong> phosphorus added to the soil through <strong>organic</strong>s i.e.,
79.90 kg per ha per year.
Among the soils from jowar based cropping systems, the highest increase in available
phosphorus content over conventional <strong>farming</strong> was observed in soils <strong>of</strong> R1 farmer (27.90%)
and it was due to addition <strong>of</strong> more quantities <strong>of</strong> phosphorus to the soil through <strong>organic</strong>s
(58.80 kg P/ha/year).