Abstract: A field investigation was carried out to compare the efficiency of different phosphatic fertilizers in salt affected soils at three different locations. Sites First and 2nd were saline sodic having coarse texture (loamy sand) while site third was sodic in nature and have fine texture (clay loam).All the sites were low in organic matter contents and extractable K while available P was in medium range. The sources of phosphorus tested were single super phosphate (SSP), triple super phosphate (TSP), diammonium phosphate (DAP) and nitrophos (N/P).The rate of phosphorus applied was 110 kg P2O5 ha-1 from all the sources along with N and K @ 140 and 70 kg ha-1 respectively. The results showed that grain and straw yields were improved by the application of phosphorus over control from all the sources. All the sources remained at par with each other at all the sites except DAP at site three (sodic) where it was found inferior to other sources used i.e. SSP, TSP and N/P. Phosphorus concentration in grain and straw was found non significant in all the treatments. While phosphorus (P) uptake was significantly affected by the phosphatic fertilizers application. Maximum P uptake was recorded in the treatment where TSP was applied except in grain at Ist site and in straw at 3rd site where SSP proved better. However both the sources remained at par with each other. Nitrophos in case of grain remained at par with TSP and SSP while in case of straw it was significantly inferior to TSP and SSP. Diammonium phosphate (DAP) was proved an inferior source at site Ist and 3rd than TSP and SSP. However P uptake in all the sources was significantly higher than control.
Introduction
At present about 6.3 million hectares of land are salt affected in Pakistan (Khan, 1993). Out of this, about 60% salt affected soils are saline sodic in nature (Muhammad, 1983). Phosphate is made unavailable in arid soils principally as complex calcium compounds. It depends in large measure on the concentration of Ca2+ ions in the soil solution, where as in sodium dominated soils the situation is more acute as sodium phosphates are quite soluble. According to Latkovics (1977) sodic soils are low in available phosphorus and plants seem more tolerant to sodicity where the phosphorus supply is maintained at higher level of available phosphorus. The shortage of phosphorus supply for plants may be due to the fact that the actual content is small, but also because of transformation of phosphorus into slowly soluble compounds. The lower phosphorus supply to plants is due to lower level of available phosphorus in soil and slow rate of transformation to replenish the loss of P due to plant uptake. The phosphorus availability is further influenced by a number of soil and plant characteristics, such as pH, CaCO3 content, moisture clay content, ESP, cation exchange of the root, pattern and rate of planting (Datta et al., 1971). More over the nutrient application level is very low in Pakistan (World Bank, 1992) and the consumption of phosphorus hardly exceeds 21.6% (NFDC, 1991). Crops grown on these soils invariably suffer nutritional and ionic disorders (Feigin, 1985). In saline/sodic environments, the availability and uptake of P assumes serious dimension (Chhabra et al., 1981). It has been noted that grain yield of rice increased with the application of P in saline-sodic/soils (Jalil et al., 1979). The yields of rice and wheat were not affected by P application in individual year in uncultivated sodic soil, but over a period of 6 years the yield of fertilized plots was more than the corresponding controls (Chhabra, 1985). Smith and Spenche (1974) in pot trials noticed that single super phosphate increased the grain yield of wheat in 47 out of 71 trials. Ahmad (1988), compared different P sources in a pot study, observed better P uptake, grain and straw yield of wheat with application of single super phosphate. Niazi et al. (1992) noted that the P sources improved the productive tillers, grain and straw yields of rice and wheat, single super phosphate remained superior. The increasing sodicity levels decreased the number of tillers, grain and straw yields and P uptake. Applying P fertilizer in sodic soil increased phosphorus uptake, being maximum for SSP followed by TSP, DAP, NP and the control. Mehdi et al. (2001) while studying the comparative efficiency of different P-carriers in mildly saline sodic soils found that grain and straw yields, P concentration in grain and P uptake by grain and straw was increased significantly over control by the application of different sources of Phosphorus. All the sources remained at par with each other in all the characteristics studied. However a careful scrutiny of the data showed maximum grain, straw yields, P concentration in grain and straw and P uptake by grain and straw were with TSP followed by SSP, N/P and DAP. TSP appears a better source of phosphorus in mildly saline sodic soil. Bajwa et al. (1990) reported that phosphate was equally efficient agronomically as single super phosphate (SSP) for rice but less so by 15 and 27% for wheat and maize respectively. The highest grain and straw yields of rice were recorded with the application of TSP, DAP and SSP compared with NP. However NP showed significant response for these parameters compared with control. Ranjha and Mehdi (1992) studied the effect of sources and methods of phosphorus application on the growth of maize and wheat. The results indicated that grain yield increased significantly with phosphorus fertilization. There was no effect of sources of phosphorus, Single super phosphate showed slightly better performance when applied in band. Thus water soluble sources, in optimum dose, showed no effect on grain yield of maize and wheat. Munir et al. (1988) also found that at ESP 40.7, SSP improved wheat yield significantly than DAP and N/P. Sajjad et al. (2001) studied the efficiency of different phosphates in salt affected soils using rice as test crop and observed that paddy and straw yields, phosphorus concentration in paddy and straw remained non-significant among sources but significant over control. Phosphorus uptake by paddy and straw was significantly higher than control in all the sources. Among sources N/P remained inferior to other sources. Observation indicated that SSP was the superior one followed by TSP, DP and N/P in improving all parameters although non significantly. Khalid (1997) also compared the efficiency of different phosphorus sources and found that all the sources of P applied significantly increased the P contents of rice straw and paddy as compared with the control. TSP showed significantly higher P contents than N/P. All the other sources were at par with one an other and were non significant with TSP and NP.
Materials and Methods
A field investigation was carried out to compare the efficiency of different phosphatic fertilizers in salt affected soils at three different locations. For this purpose three sites were selected. Sites Ist and 2nd were selected at Soil Salinity Research Institute, Pindi Bhattian research farm and were saline sodic having loose texture (loamy sand) while site 3rd was selected at farmer field near Pindi Bhattian and was sodic in nature having heavy texture (clay loam). The sources of phosphorus tested were single super phosphate (SSP), triple super phosphate (TSP), diammonium phosphate (DAP) and nitrophos (N/P).The rate of phosphorus application was 110 Kg P2O5 ha-1 from all the sources along with N and K @ 140 and 70 Kg ha-1 respectively. Wheat variety inqulab- 91 was sown at all the sites. Same cultural practices were applied to all the sites. Crop was harvested at maturity and grain and straw yield data were recorded. Grain and straw samples were analysed for phosphorus contents and p uptake was calculated by using the following formula.
All the analyses were done according to the methods given in hand book NO.60 (U.S.Salinity Lab. Staff, 1954) except texture by Moodie et al. (1959), available P in soil by Watanabe and Olsen (1965).The data were statistically analysed by using randomized complete block design (RCBD) according to techniques prescribed by Steel and Torrie (1980).
Results and Discussions
Grain and straw yield
This experiment was conducted at three sites i.e. two at SSRI research farm
and were saline sodic having loose texture (loamy sand) while third was at farmer
fields near Pindi Bhattian and was sodic in nature having heavy texture (clay
loam). All the sites were low in organic matter contents and extractable K while
available P was in medium range (Table 1).
Grain and straw yield data is given in Table 2. The results indicated that there was a significant increase in grain and straw yield over control by the application of phosphorus from all the sources. All the sources remained non significant with each other except DAP at site three where soil was sodic and heavy in texture (clay loam). The non significant differences among the sources were also noted by Mehdi et al. (2001) in saline sodic soils while Niazi et al. (1992) observed non significant differences among the sources of P in sodic soils.
| Table 1: | Original soil analysis of the sites |
| Table 2: | Grain and straw yield of wheat (t ha-1) |
The reason for low efficiency of DAP in heavy textured sodic soils might be that at high ESP, above 20 and at low level of fertilizer P application ,there is a negative sorption of P by the Alkali soils (Chhabra, 1988). Pratt and Thorne (1948) observed increased P solubility with increase in pH and Na-dominated clay system while in Ca-dominated system it decreased. Thus more water soluble sources may be applied in sodic soils. A careful observation of the data indicated that TSP remained superior at sites 1 and 3 to produce maximum grain and straw yields except straw at site three which was produced more by SSP while SSP produced maximum grain and straw yields at site 2 indicating the superiority of SSP and TSP over DAP and N/P although non significantly.
Phosphorus concentration in grain and straw
Phosphorus concentration in grain and straw (Table 3)
remained at par at all the sites. However P concentration in control treatment
was much less than the P applied plots. A careful observation
of the data indicated that maximum concentration in grain at site one and three
was noted by SSP while at site 2 by TSP where as SSP gave higher concentration
un straw at site 3 while TSP gave higher P concentration at site one and two
indicating the superiority of SSP and TSP over DAP and N/P although non significantly.
Niazi et al. (1992) and Mehdi et al. (2001) also noted similar
findings.
Phosphorus uptake by grain and straw
Phosphorus uptake by grain and straw (Table 4) was significantly
increased over control by the application of phosphorus. Maximum phosphorus
uptake was noted in TSP treated plots except grain at site 1 and straw at site
3 where SSP remained superior. Diammonium phosphate(DAP) was significantly inferior
at all the sites studied except P uptake in grain at site 2 where it was at
par with other sources tested. While N/P was at par with TSP and SSP except
P uptake by straw at sites 1 and 2. However TSP proved to be superior source
of P followed by SSP, nitrophos and least by DAP. Mehdi et al. (2001)
also recorded similar results.
| Table 3: | Phosphorus concentration (%) in grain and straw |
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| Table 4: | Phosphorus uptake by grain and straw of wheat (kg ha-1) |
While Niazi et al. (1992) found SSP as superior source in highly sodic soils having ESP of 41 but in the present study TSP was found superior source of phosphorus. As SSP and TSP are highly water soluble so performs better than DAP or N/P which are citrate soluble. More over Dap has high pH and did not offer relief, comparable to acid fertilizer, to plant in calcareous saline sodic/sodic soils, so it was found least efficient chemical influencing P uptake by wheat plants.
Wheat yield and phosphorus concentration were significantly affected by different P sources as compared to control. This supports the conclusion drawn by other workers that P application has important role in increasing grain and straw yield of wheat.
Different sources used did not show any significant edge over each other except DAP in heavy textured soil (clay loam) where it was inferior to other sources used. These are preliminary results and further confirmation is required before making any recommendation for the farmers.