Publisher Summary Because of their controlled-release properties, phosphate rocks (PRs) are ideally suited for long-term crops such as permanent pastures and plantation crops. In very acidic soils, they may be effective even on seasonal crops. On long-term crops, a time lag is likely between the time of application of PR and its adequate availability to plants. The time lag can, however, be shortened by amending PRs; it also overcomes the need for greater soil acidity for effective use of PRs on seasonal crops. Application of PRs could be more widespread if the resulting yield increases are predictable and profitable. This would aid in the economic development of countries, especially those with indigenous PRs resources, and minimize pollution in industrialized countries. To achieve predictability of PRs effectiveness, a network of long-term experiments should be established at well-characterized sites and the rate of PRs dissolution and agronomic yield parameters should be measured. Further development and application of models similar to those described in this chapter should be able to relate soil and site properties with dissolution of PRs and their agronomic and economic effectiveness. This chapter concentrates on the advances made on the fundamentals of PRs dissolution and their agronomic use, with specific examples.

Phosphate rocks for direct application to soils.

Biochar had effects on phosphorus sorption and desorption in three soils with differing acidity

Crop yields, soil fertility and phosphorus fractions in response to long-term fertilization under the rice monoculture system on a calcareous soil

http://ir.yic.ac.cn/bitstream/133337/6480/1/What%20is%20more%20important%20for%20enhancing%20nutrient%20bioavailability%20with%20biochar%20application%20into%20a%20sandy%20soil%20Direct%20or%20indirect%20mechanism.pdf

What is more important for enhancing nutrient bioavailability with biochar application into a sandy soil: Direct or indirect mechanism?

The agronomic effectiveness of phosphate fertilizers is strongly affected by reactions of P with soil constituents. The transformation of P added to soil and the effect of soil properties on these transformations was investigated for 14 alkaline and calcareous soils from southern Western Australia. The decline of NaHCO 3 -extractable P (Olsen-P) with time followed a second order kinetic equation. The kinetic rate constant (k) increased with increasing oxalate-extractable Fe (Fe o ), citrate-dithionite-bicarbonate (CDB)-extractable Al and Fe (Al d and Fe d ), CaCO 3 -free clay content, cation-exchange capacity (CEC), and ratio of CDB-extractable Fe (Fe d ) to active CaCO 3 equivalent (ACCE), and k decreased with increasing ACCE. A combination of these soil properties described 93% of the variation in rate constant, of which 78% of the variation was predicted by the Fe d /ACCE ratio alone. A combination of clay related properties (Al d , clay, Fe o , and CEC) described 62% of the variation in Ca 2 -P determined by specific extraction. Carbonate-related properties (ACCE and CCE) together described 71% variation in Ca 8 -P. Clay-related and carbonate-related properties jointly described 97% and 81% of the variation in Fe-P and Olsen-P respectively. Surface area (SA) and Al d together accounted for 43% of the variation in Al-P. Scanning electron microscopy analyses showed that added P was uniformly distributed in the soil matrix to the limit of the spatial resolution of the technique ( 2. μm).

Phosphorus Transformations and Their Relationships with Calcareous Soil Properties of Southern Western Australia

On the basis of a critical review on conventional fractionation schemes of inorganic phosphate and further study of chemical behaviors of Ca-P and Fe-P in calcareous soils, a systematic scheme for the separation of soil inorganic phosphates in calcareous soils is suggested. In the scheme calcium phosphate is classified into dicalcium phosphate, octacalcium phosphate and apatite types, and Ca2-P is extracted by NaHCO3 solution, Ca8-P by NH4Ac, Al-P by NH4F, Fe-P by NaOH-Na2CO3, occluded-P by Na3Cit-Na2S2O4-NaOH, and Ca10-P by H2SO4. Synthetic phosphates prepared of which the chemical and physical assay show good consonance with the theoretical value were used in experiment, the recovery rates of the phosphates added into the calcareous soils by specific extractants is at the range of 85–99%.

Jiang Baifan

Papers

A suggested fractionation scheme of inorganic phosphorus in calcareous soils