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Phosphorus in South Indian Agriculture
By T. Nagendra Rao
Research experiences in the past are clearly indicating that soils having low P status respond largely to P fertilization compared to high P status soils. This trend is common irrespective of soil groups although the degree of response may vary (Table 1).
Table 1: Yield response of rice to phosphorus application grown in important soil groups of southern region
| District & State | Soil Group | No. of Trials | Soil Critical Limit for P (Olsen P2O5 kg/ha) | Rice Yield Response (kg/ha) to P application at 60 kg/ha P2O5 dose |
Below Critical Limit | Above Critical Limit |
| Shimoga (Karnataka) | Red | 25 | 15 | 2078 | 140 |
| Chittor (Andhra Pradesh) | Red | 17 | 18 | 3187 | 648 |
| Nizamabad (Andhra Pradesh) | Deep Black | 38 | 30 | 1102 | 711 |
| West Godavari (Andhra Pradesh) | Medium Black | 30 | 33 | 1954 | 760 |
| Allepy (Kerala) | Coastal Alluvium | 39 | 67 | 521 | 104 |
Primary Source: Goswami et. al., 1971; Secondary Source: Singh & Sharma, 1994
As per the revised information on soil P fertility status, 70 percent of total 63 districts in four southern states are low in available phosphorus and 30 percent in medium status. None of the districts have high P fertility status, indicating the extent of the phosphorus requirement of these soils (Table 2 ).
Table2: Distribution of southern districts according to the soil phosphorus fertility classes
| State | Number of districts for which soil test obtained | Phosphorus Fertility Classes |
Low | Medium | High |
| Andhra Pradesh | 21 | 17 | 4 | -- |
| Karnataka | 19 | 16 | 3 | -- |
| Kerala | 10 | 3 | 7 | -- |
| Tamil Nadu | 13 | 8 | 5 | -- |
Source: Hasan, 1996 (Ref: Hasan, R. 1996 Better Crops International 10(2), 4-5)
The information above indicates that crops grown on these soils have a large P requirement and response to P fertilization could be considerable.
Response to P application - PPIC-India Programme Experience
India Programme supports various research projects in the region with the view to generate information on the response of various crops to P and K fertilization. The Table below illustrates how crops respond to P fertilization. Besides the essential nature of P in staple food crop production, P fertilization is especially remunerative with cash crops and high value crops.
STATE | CROP | PHOSPHORUS DOSES (P2O5 kg/ha) | YIELDS (t/ha) | NET RETURNS (Rs./ha) | REMARKS |
| Andhra Pradesh | Hybrid Rice | 60 | 6.54 | 14,215 | Data average of two years (1997-98 & 1998-99).
N and K2O applied @180 & 210 respectively as common dose.
Additional cost of 45 kg P2O5 was Rs. 672 |
105 | 7.51 | 17,811 |
| Tamil Nadu | Cotton Hybrid (TCHB 213) | 0 | 2.62 | 38,558 | N and K2O applied @ 200 kg/ha as common dose. Yields are of seed cotton |
75 | 3.45 | 58,092 |
Cotton Variety
(MCU 5) | 0 | 1.97 | 22,783 |
75 | 2.32 | 30,267 |
| Kerala | Ginger | 0 | 14.8 | 98,990 | Common doses of N-K2O-S-B : 150-100-15-2 applied commonly. Average of two years data (1998-99 & 1999-200) |
25 | 16.5 | 120,032 |
50 | 16.0 | 119,478 |
75 | 17.2 | 126,739 |
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