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

In sugarcane based cropping system, the highest increase in phosphorus content due
to <strong>organic</strong> <strong>farming</strong> was recorded in soils <strong>of</strong> S3 farmer (33.10%), which could be ascribed to
the addition <strong>of</strong> 88.80 kg P per ha per year through <strong>organic</strong>s and long-term <strong>organic</strong> manuring
(10 years).
In vineyards, the highest increase in available phosphorus content due to <strong>organic</strong>
<strong>farming</strong> was recorded in soils <strong>of</strong> V3 farmer (30.23%). Addition <strong>of</strong> higher quantity <strong>of</strong>
phosphorus (74.20 kg P/ha/year) to the soil through <strong>organic</strong>s was responsible for build up <strong>of</strong>
available phosphorus in the soil.
5.4.3 Available potassium
Data on available potassium content <strong>of</strong> soils under different cropping system (Table
16) revealed that all soils were high in available K in both conventional and <strong>organic</strong> <strong>farming</strong>.
However, soils under <strong>organic</strong> <strong>farming</strong> recorded slightly higher available potassium than those
under conventional <strong>farming</strong>. The increase in available potassium in soils <strong>of</strong> <strong>organic</strong> farms
could be attributed to the direct addition <strong>of</strong> potassium to the available pool <strong>of</strong> the soil from
FYM and vermicomposts. The beneficial effect <strong>of</strong> FYM on the available potassium might be
also ascribed to the reduction <strong>of</strong> potassium fixation (Tandon, 1988). Similar observations <strong>of</strong>
increase in available potassium due to addition <strong>of</strong> <strong>organic</strong> manures were made by Grawel et
al. (1981) and Bharadwaj and Omanwar (1994).
On an average, the per cent increase in available potassium in soil under <strong>organic</strong>
<strong>farming</strong> over conventional <strong>farming</strong> was slightly more than 4.00 per cent in cotton, kharif jowar
and sugarcane based cropping systems, 3.20 per cent in rabi jowar and 2.64 per cent in
vineyard system. Although, the <strong>organic</strong> manures applied to soil under <strong>organic</strong> <strong>farming</strong>
practice added substantial quantity quantity <strong>of</strong> potassium to the soil (70.60 in case <strong>of</strong> V2 farm
to 159.60 kg/ha/year in case <strong>of</strong> S3 farm), the increase in its availability in soil was not high. All
the soils studied were Vertisols which are known to have higher K fixation capacity and this
could be the reason for lower increase in K availability inspite <strong>of</strong> addition <strong>of</strong> K through
<strong>organic</strong>s.
5.4.4 Available sulphur
The soils under <strong>organic</strong> <strong>farming</strong> recorded higher values <strong>of</strong> available sulphur content
than soils under conventional <strong>farming</strong>, irrespective <strong>of</strong> cropping system followed (Table 17).
The average increase in available sulphur in soils <strong>of</strong> <strong>organic</strong> farms was higher by 3.60 (kharif
jowar) to 10.40 (cotton) per cent over conventional farms. Increased available S in soils <strong>of</strong>
<strong>organic</strong> <strong>farming</strong> was due to the addition <strong>of</strong> sulphur through the <strong>organic</strong> manures applied to the
soil after decomposition. Vadiraj et al. (1992) attributed the increase in available S content to
the release <strong>of</strong> <strong>organic</strong> bound sulphur through mineralization.
Among different cropping systems, the highest increase in available sulphur was
observed in soils <strong>of</strong> C 4 farmer in cotton based cropping system (14.30%). R 1 farmer in jowar
based cropping system (6.50%), S3 farmer in sugarcane based cropping system (10.00%)
and V3 farmer in vineyards (5.23%). Addition <strong>of</strong> higher quantities <strong>of</strong> <strong>organic</strong> manures and/or
longer period <strong>of</strong> <strong>organic</strong> practice by above farmers were probably responsible for buildup <strong>of</strong>
available sulphur in soil.
5.4.5 DTPA-extractable micronutrients
The data on DTPA-extractable micronutrients in soils studied (Table 18, 19, 20, 21,
22, 23, 24 and 25) revealed that concentration <strong>of</strong> available Zn, Fe, Mn and Cu in all the soils,
irrespective <strong>of</strong> type <strong>of</strong> <strong>farming</strong> or cropping system was above critical limits. But, however, the
soils under <strong>organic</strong> <strong>farming</strong> recorded much higher concentration <strong>of</strong> the micronutrients than
soils under conventional <strong>farming</strong> in all the cropping systems. The overall increase in
availability <strong>of</strong> zinc, iron, manganese and copper ranged from 31.45, 32.45, 23.58 and 16.70
per cent, respectively in soils <strong>of</strong> vineyards to 47.80, 39.88, 27.77 and 26.66 per cent,
respectively in soils <strong>of</strong> kharif jowar. Addition <strong>of</strong> large quantities <strong>of</strong> <strong>organic</strong> manures every year
under <strong>organic</strong> <strong>farming</strong> practice was the cause for such marked increase in the DTPAextractable
micronutrients. Bellakki and Badanur (1997) attributed the increase in
micronutrients in soils with addition <strong>of</strong> <strong>organic</strong>s to the enhanced microbial activity and