ISSN:
1573-0867
Keywords:
agronomic effectiveness of rock phosphates for rice
;
citrate solubility
;
F and CO3 substitution for PO4 in rock phosphates
;
unit cell dimension
Source:
Springer Online Journal Archives 1860-2000
Topics:
Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
Notes:
Abstract Comparative reactivity and efficiency of eight Indian, six US, two African and one Middle East sources of rock phosphates for growing rice on laterite, red and alluvial soils under flooded conditions were evaluated in pot and laboratory experiments. When applied to moist aerobic soils, 15 days prior to flooding and transplanting rice, all the Indian sources were as poor as theno phosphate control in the three soil types, in respect of P availability in soil, grain yield response and P uptake by rice. North Carolina rock phosphate used in this study was as good as superphosphate in the laterite and red soils, but was also as poor as control in the black soil. NH4 -citrate was found to interfere in the colorimetric determination of citrate soluble P by the vanado-molybdate colour method. A modified sulpho-molybdate-Sn Cl2 blue colour method could successfully be used to determine 2–8µg P in the presence of 0.02 to 0.2 meq NH4 -citrate, especially in rocks containing small amounts of citrate soluble P. All the Indian, as well as Idaho, Missouri and Tennessee rock phosphates were found to be less reactive as they contained much lower amounts of citrate extractable P in eight successive extracts as compared to North Carolina rock phosphate. The cumulative citrate soluble P of 10 rock phosphates determined experimentally in eight successive extracts was significantly correlated with their reported a0 (length of ‘a’ axis of unit apatite crystal), mole ratio of CO3/PO4 or weight ratio of F/P2O5 of rocks. In the absence of X-ray and computer facilities, these regression equations were used to calculate the a0, CO3/PO4, F/P2O5, ACS, empirical formula and the apatite content of the unknown Indian rock samples. The Indian rock phosphates had a lower degree of CO3 and F substitution for PO4 in the apatite crystal, giving low ACS values and hence were less reactive. This might explain their lower efficiency for direct application for growing rice, obtained in the present experiment. These Indian rock phosphates had also lower apatite content. The use of the statistical method was limited to francolites alone. Scope for the use of this method for other unknown francolite rock phosphate samples has been discussed.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF01082977
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