Application of Phosphorus in Soil: Increase Doulble Production

Phosphorus (P) inputs are required for sustainable agricultural production in most acid soils of the tropics and subtropics. Phosphate rocks (PR) and organic materials have been suggested as alternative P sources in these soils. Quantitative information on the P availability from sewage sludge (SL) is scanty. Methods to improve the effectiveness of PR such as partial acidulation and compaction with water-soluble P sources have been recommended. The objective of this greenhouse study was to evaluate the relative agronomic effectiveness (RAE) of Florida PR and sewage sludges (irradiated and non-irradiated) applied alone and in mixture with a water-soluble source (triple superphosphate, TSP) at two rates (50 and 150 mg P kg^-1 soil). The ³²P isotope dilution technique was utilised to determine the proportion of P in the plant taken up from the P fertilizer treatments. Wheat was grown on an acid loamy sand Dystric Eutrocrepts and harvested 6 weeks after planting. Results on total P uptake and the RAE of the P fertilizer sources tested indicated that the addition of 50 mg P kg^-1 soil as TSP was adequate in supplying P to the 6-week-old wheat plants as compared to PR and sewage sludge. Intermediate values were obtained for the mixtures. Similar responses were observed for the high P rate. For a given P rate, phosphorus uptake from PR and SL in presence of TSP was higher than P uptake from these sources alone, indicating an enhancement effect of TSP on the effectiveness of these non-readily available sources. With respect to P uptake from PR applied alone, the relative increases in P uptake from PR due to TSP influence were 52 and 67% for the low and high P rates, respectively. The relative increases in P uptake from SL due to TSP when compared to P uptake from SL alone were 102 and 59% for the low and high P rates of application. Application of a water-soluble P fertilizer together with a non-readily available P source shows an enhancement on the P uptake from the non-readily available P source by the wheat plants. In this experiment the estimated enhancement effects are very likely underestimated.

 

SOIL ACIDITY

Soil acidity affects the growth of pasture and crops in the following ways:

• Aluminum and manganese become more soluble (available) and may reach toxic levels to reduce plant growth below pH 4.8. At or below this pH aluminum will reduce root growth while manganese disrupts photosynthesis and other functions of growth.

• Nitrogen fixation by nodule inhabiting bacteria (Rhizobia) located in legume roots is reduced in very acid soils. The effect of the acidity varies for different strains, for example, the Rhizobia associated with lucerne fix most nitrogen at a pH range of 6.3 to 7 whereas the lupin Rhizobia function well at pH 4.0.

• Breakdown of organic matter to release valuable nutrients slows when acidity adversely affects the decomposing organisms. The cycling of organic matter is therefore slower in acid soils, reducing the availability of the major elements, nitrogen, phosphorus and sulfur.

• The important trace element molybdenum (Mo) becomes increasingly less available as pH declines below 5.0. Mo deficiency reduces nitrogen fixation and subsequent pasture quality and bulk.

• Acidity severely restricts plant responses to applications of other nutrients, by reducing either the availability of essential nutrients or the effectiveness of the roots to obtain nutrients and moisture.

• Leaching of acidity into the lower soil layers increases once pH declines below 5.0 leading to an acidified sub soil that cannot be easily corrected.

 

EFFECT OF pH ON P AVAILABILITY

Research shows that P is most readily available between pH 6 and 7. Availability is governed by solubility and how readily P becomes tied up (fixed) in soils. Fixation onto colloidal iron surfaces at very low pH levels, usually below 4, is seldom the dominant P fixation process. P fixation with aluminum is more commonly seen from pH 4.5 to 6 and results in substantial lock-up of P, while in less acid to neutral pH soils calcium phosphate is the more commonly encountered inorganic form of P.

There is a relationship between soil type and pH in terms of P fixation. Soil pH below 5.5 affects solubility (availability) of P in soils characterized by cracking clays, where aluminum and iron dominate. Above this level, calcium and magnesium are the dominant ions and fixation is less permanent.

 

Applications of Optical tweezers

·         Optical tweezers are a powerful tool for manipulation and investigation of microscopic particles.

·         Optical Tweezers have been used to trap dielectric spheres, viruses, bacteria, living cells, organelles, small metal particles, and even strands of DNA.

·         Applications include confinement and organization (e.g. for cell sorting), tracking of movement (e.g. of bacteria), application and measurement of small forces, and altering of larger structures (such as cell membranes). 

BisBismark Bangali

BSC  in Agrotechnology 

 

 Khulna University.