rather than only in the testing of technologies
CASE 7: Phosphogypsum (PG) as soil conditioner to improve barley yields through farmer's participatory evaluation
Rationale and background
PG is residue product of the phosphorus fertilizer industry, and is available in large quantities in Syria. PG is known as a soil conditioner and improves the physical and chemical characteristics of soils.
The beneficial effect of surface application of PG in soils is: maintaining high water infiltration, increasing the water holding capacity of the soil, and reducing water runoff and soil loss by erosion (Agassi et al., 1990). Warington et al., (1989) reported similar observations and found that PG surface application reduced soil erosion by 10-40% more than the control. It also promotes soil flocculation, enhances aggregate stability and deposition of entrained particles by runoff (Agassi and Ben-Hur, 1991).
PG has been also used as a source of Ca, P, and S (Nogueira and Melo 2003; Ghosh and Sarkar 2000) on a broad range of soils differing in pH and fertility. PG is an effective nutrient source since it increases water-soluble Ca, K, and P concentrations (essential plant nutrients). At the same time, PG significantly reduces soluble aluminum, thereby reducing aluminum toxicity to plants (Carbonell et al., 1999).
PG also has the capacity to supply relatively large amounts of soluble nutrients during critical phases of crop growth (Malavolta et al., 1987; Bianco et al. 1990; Gascho and Alva, 1990; Singh et al., 1990). While P2O5 comprises less than 1% of PG material, high application rates may significantly increase P availability in soil (Broadbent et al., 1989; Khalil et al., 1990). PG increased the availability of Fe and Mn through a localized acidifying action around the roots, and increased the availability of N, P, K, and Mg in calcareous soils (Singh et al. 1990, Khalil et al., 1990).
Objectives:
The trial was designed in a participatory approach with different farmers at different sites in the Khanasser Valley to evaluate the possible use of PG as a soil conditioner by the following determinants:
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1-
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Assess the effect of PG addition to soil on barley
production
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|
2-
|
Assess the effect of PG addition to soil on F (Fluoride)
contents, and the radioactivity in the barley products
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|
3-
|
Assess the effect of PG addition to soil on some soil chemical and physical properties, its radioactivity and Fluoride content |
|
4-
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Assess the effect of sites and farmers on barley response to PG addition to soil |
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5-
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Determine the costs and benefits of using PG as a soil conditioner |
|
5-
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Assess the effect of TSP application to soil on barley production relative to PG application. |
Methodology:
The trials were conducted at 8 different locations with 8 different farmers in Khanasser valley: (1) Al-Mugherat village, (2) Al-Qura`a village, (3) Al-Hawaz village, (4) Serdah village, (5) Al- Kurbatieh village (2 sites), and (6) Al- Rashadieh village (2 sites).
PG was broadcasted by hand and incorporated into the soil by discharrow. Crop rotations were 2-course Barley/Barley and Barley/Fallow. Local Barley (Hordeum sativum var. local black) seeds were sown at a rate of 100 kg ha-1 on November by a Plot drill with roller behind. The experiment included 3 treatments of PG: 0, 20 and 40 t ha-1 with two replicates arranged in a complete randomized block design. Soil samples were collected from all sites and from 3 depths; 0 -15, 15-30, and 30-45 cm, to determine the physical and chemical properties, Fluoride content and the radioactivity of the soil. Chlorophyll content, plant height and number of tillers in each replicate were determined. Grain and straw production of barley were measured and a chemical analysis and radioactivity measurement performed.
Results:
The first year (2001/02) result of 118 mm of very low rainfall shows that adding PG significantly increased the total biomass and grain yield of continuous barley compared to the control (Table 1). Comparison between the effects of the 40 t/ha PG and the P fertilizer applications show that PG resulted in a better crop response: 40% higher for biomass and 36% higher for barley grain yield.
In the second year (2002/03) with higher rainfall (302 mm), results show that the residual effect of PG application continues to have positive effects on the total biomass and grain yield of barley compared to the control. This is similar to the first year results though to lesser extent (Table 1):
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•
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Under continuous barley system, comparison between
the effects of 40 t/ha PG and the P-fertilizer applications show
that PG resulted in only slightly better crop response: 3% higher
for biomass and 6% higher for barley grain yield. However, PG applications
increased both the barley biomass and grain yield significantly
by 33-43% compared to the control with no additional cost unlike
the case of P-fertilizer.
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|
•
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Under barley-fallow system, PG applications increased
the barley grain yield significantly by 46-48%, compared to the
control plots. There was no P-fertilizer application under barley-fallow
systems.
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The third year (2003/04) with higher rainfall (250 mm) result shows that the residual effect of PG application also continued to have positive effects on the total biomass and grain yield of barley compared to the control. This is similar to the second year results though to lesser extent (Table 1):
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•
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Under continuous barley system, comparison between
the effects of 40 t/ha PG and the P-fertilizer applications show
that PG resulted in slightly less crop response: 3% lower for biomass
and 1.5% lower for barley grain yield. Thus, the effect of PG is
getting less every year compared to Phosphate fertilizer. But PG
applications provided 22-31% grain yield increase compared with
the control with no additional cost as similar to the second season.
However, P-fertilizer has a high cost but PG has no cost on the
second and the third season.
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|
•
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Under barley-fallow system, PG applications increased
barley grain yield significantly by 41-47%, compared to the control
plots, which shows that PG is still very effective for the third
year in a row. There was no P-fertilizer application under barley-fallow
systems.
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The three year results would indicate that the benefit of PG is not only caused by the additional phosphorus, but that also the soil physical conditions are improved. This would be especially beneficial for the early crop growth. Soil moisture measurements showed that adding PG to soil increased water content (0-60 cm profile) from about 20 to 22%, while P- fertilizer had no effect on the water content compared with the control, which was beneficial during the flowering and grain filling periods, particularly in dry year like 2001/02. Partial budget analysis indicated that the transport cost of PG with 500 SP/ton would make the first year benefit neutral, but the remaining years would be all for the farmers' benefits. However, P-fertilizer application each year would be either neutral or negative for the farmers' benefits.
Table 1: Effect of phosphogypsum (PG) application on barley yields with respect to rotation during 2001/02 to 2003/04 seasons (N=8).
| Cropping Systems/Treatments |
Barley grain yield (kg/ha)
|
Grain yield increase over
the control (%)
|
Barley total biomass (kg/ha)
|
|
Average (SD)
|
Average
|
Average (SD)
|
|
| Treatments |
2001/02 (Barley/Barley)
|
||
| Control |
630 (135)
|
-
|
1325 (137)
|
| P2O5 (50 kg/ha) |
775 (179)
|
+23
|
1580 (350)
|
| PG (20 t/ha) |
930 (290)
|
+48
|
1970 (398)
|
| PG (40 t/ha) |
1055 (366)
|
+67
|
2220 (430)
|
| Treatments |
2002/03 (Barley/Barley)
|
||
| Control |
1630 (975)
|
-
|
3400 (2110)
|
| P2O5 (50 kg/ha) |
2245 (580)
|
+38
|
4955 (1675)
|
| PG (20 t/ha) |
2170 (895)
|
+33
|
4620 (2125)
|
| PG (40 t/ha) |
2325 (1010)
|
+43
|
5075 (2790)
|
| Treatments |
2003/04 (Barley/Barley)
|
||
| Control |
775 (128)
|
-
|
1725 (597)
|
| P2O5 (50 kg/ha) |
1035 (169)
|
+33
|
2265 (722)
|
| PG (20 t/ha) |
950 (191)
|
+23
|
2055 (659)
|
| PG (40 t/ha) |
1020 (229)
|
+32
|
2200 (860)
|
| Treatments |
2002/03 (Barley/Fallow)
|
||
| Control |
2245 (820)
|
-
|
4720 (2095)
|
| P2O5 (50 kg/ha) |
-
|
-
|
-
|
| PG (20 t/ha) |
3285 (980)
|
+46
|
6900 (2300)
|
| PG (40 t/ha) |
3315 (1095)
|
+48
|
6970 (2640)
|
| Treatments |
2003/04 (Barley/Fallow)
|
||
| Control |
1110 (275)
|
-
|
2375 (733)
|
| P2O5 (50 kg/ha) |
-
|
-
|
-
|
| PG (20 t/ha) |
1570 (634)
|
+41
|
3640 (1412)
|
| PG (40 t/ha) |
1635 (651)
|
+47
|
3925 (1518)
|
Radioactivity:
The radioactivity measurements show that adding PG (containing 416 Bq kg-1 Ra-226) to the soils increased the radioactivity of the upper layer (0-15 cm) by 5 and 9 Bq kg-1 for 20 and 40 t ha-1 respectively compared with the background radiation level of 20 Bq kg-1, while the other layers (15-30 and 30-45 cm) were not affected. According to the Atomic Energy Commission of Syria, the permissible limit of Ra_226 in the soil must not exceed 150 Bq/kg DW. In spite of the increased radioactivity of the soil, the radioactivity of barley's straw and grains were below the detectable limit (about 2 Bq kg-1 of dry matter). Thus, after the three years of PG application, radioactivity levels are much below the permissible limits for both soil and crop.
Farmers' participatory evaluation:
Participatory Technology Evaluation (PTE) was conducted to evaluate the farmers' perception on the impact of PG on barley growth, and to identify technological, economical, and other problems related to PG application. All the participating farmers together with other interested farmers evaluated the PG very effective for increasing barley yield, under both continuous barley and barley/fallow systems. A farmer in Alqara site used manure (10 t/ha) three years ago on the adjacent field on cumin in 2002 and used a crop rotation of cumin, wheat, and barley respectively. In 2003, wheat yield was 2.0 t/ha. In 2004, at the time of visit to the site, barley looked the same as the one with PG after fallow showing the similar effects of Manure and PG after the third of their applications. At the same time it was reported that only 18% of farmers applied manure because of its higher cost of about 7,000-10,000 SP/ha. Farmers also observed that the soil moisture on the 20 cm was better in 40 than 20 and no PG, which was one of the reasons for higher yields under PG application.
All farmers were interested to apply PG provided transportation would not cost more than 100 SL/ton. 77% of the farmers said they would apply 20 t/ha and only 23% opted for 40 t/ha with any associated cost, but if it was provided free they would all apply 40 t/ha of PG. Finally, they all said that PG has shown the productivity increase for the third year in a row, so it should be proposed to policy makers to find the way to transfer the materials to the closest location free of charge or with a minimum cost as they indicated.
Conclusions:
The results of the first 3 years show that PG is a promising option for the dry marginal conditions of Khanasser Valley. However, the experiment will be repeated for some more years to find out how long the effects of PG on barley yield will last. The low radioactivity levels of soil and crop much below the permissible limits after the third year of the PG application is very promising and this technology is recommended to start as early as next year. For this reason, there will be a special meeting organized by the Ministry of Agriculture, in collaboration with AECS and ICARDA, to further assess PG storage and its use in agriculture. ,Hopefully it will be concluded that the dry areas where there is a chronically deficient rainfall would get the use of the PG to increase the productivity of barley and other crops with a little cost.
References:
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Agassi, M., Shainberg, I., and Morin, J. (1990). Slope, aspect, and Phosphogypsum effects on runoff and erosion. Soil Sci. Am. J., 54.pp.1102-1106. |
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Agassi, M., and Ben-Hur, M. (1991). Effect of slope length, aspect and Phosphogypsum on runoff and erosion from steep slopes. Aust.J. soil. Res., 29.pp.197-207. |
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Bianco, S., Ruggiero, G., Vitti, GC. And P.R. Santos (1990). Effects of Phosphogypsum and potassium chloride on the nutritional status, production and orangoleptical quality of pineapple fruits. In: Proceedings of the Third International Symposium on Phosphogypsum, Orlando, Fl, FIPR. Pub. No. 01-060-083, vol. I.pp.348-361. |
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Broadbent, P., Trochoulias, I., Baigent. D.R., Abbott, T.S., and Dettmann, E.B. (1989). Effect of soil management on avocados in krasnozem soil. Sci. Hortic, 38, pp.87-104. |
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Carbonell, A.A., Porthose,J.D., Mulbah, C.K., Delaune,R.D., and Patrick,W.H. (1999). Metal solubility in phosphogypsum-amended sediment under controlled pH and redox conditions. J.Environ.Quality .Vol.28,Iss.1,pp.232-242. |
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Gascho, G.J., and Alva, A.K. (1990). Beneficial effects of gypsum for peanut. In: Proceedings of the Third International Symposium on Phosphogypsum, Orlando, FL, FIPR. Pub. No 01-060-083. Vol 1. pp.376-393. |
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Ghosh,G.K., Sarkar,A.K. (2000). Efficacy of phosphogypsum as source of sulphur for chickpea (Cicer arietinum) in an acid soil. Indian J.Agricul.Sci.Vol, 70,Iss.6.pp.403-404. |
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Khalil, N.F., Alnuami, N.M., and Jamal, M.A. (1990). Agricultural uses of Phosphogypsum in calcareous soils. In: Proceedings of the Third International Symposium on Phosphogypsum, Orlando, FL. FIPR pub. No. 01-060-083, vol.1.pp.333-347. |
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Malavolta, E., Vitti, G.C. Rosolem, C.A., Fageria, N.K., and Guimaraes. P.T.G. (1987) Sulfur responses of Brazilian crops. J. plant Nutr. 10.pp.2153-2158. |
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Nogueira,M.A., Melo,W.J. (2003). Sulphur availability to soybean and arilsulphatase activity in a soil treated with phosphogypsum. Revista Brasileira de Ciencia Do Solo.Vol.27,Iss.4,pp.655-663. |
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Singh, A.L., Joshi, Y.C., Chaudhari, V., and Zala, P.V. (1990). Effect of different sources of iron and sulfur on leaf chlorosis, nutrient uptake and yield of groundnut. Fert. Res., 24.pp:85-96. |
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Warrington, D., Shianberg I., Agassi, M.,
and Morin, J. (1989). Slope and Phosphogypsum`s effects on runoff
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