Water-soluble Phosphate Fertilizer Research Articles

Effect of phosphorus-coupled nitrogen fertigation on clogging in drip emitters when applying saline water

Emitter clogging risk might be enhanced by the specific fertigation practice when applying saline water. Two stages of on-site drip irrigation experiments applying saline water were conducted to investigate the effects of the phosphorus (P) fertigation and combined P and nitrogen (N) fertigation and the water salinity on emitter clogging when using a plain channel emitter and a labyrinth emitter. During stage one, the water-soluble phosphate fertilizers monoammonium phosphate (MAP), diammonium phosphate (DAP), and urea phosphate (UP) were tested in comparison with a control treatment without fertigation (CK). During stage two, four combined P and N fertigation practices were tested by mixing one phosphate fertilizer (MAP or DAP) with one N fertilizer (urea (U) or ammonium sulphate (AS)). Four levels of water electrical conductivity measuring about 0.5 (groundwater, G), 2 (S2), 4 (S4), and 6 (S6) dS m−1 were tested at both experimental stages. The discharge rates of the emitters were measured following every other two fertigation events during stage one and following each fertigation event for stage two. At the end of the experiments, several representative emitters were sampled to measure the dry weight and the chemical constituents of the clogging substances in the emitters. The results demonstrated that the P fertigation with a weak or a slightly stronger acidic fertilizer such as MAP or UP reduced the emitter clogging effectively during groundwater application. For saline water application, the emitter clogging clearly increased with the water electrical conductivity. Phosphorus-coupled nitrogen fertigation accelerated the precipitation of phosphate sediments greatly when either groundwater or saline water was applied. In fact, the precipitation of phosphate sediments exceeded 80% of the dry weight in the emitters under saline water irrigation. Rapid development of emitter clogging occurred for both types of emitters when saline water with electrical conductivity higher than 4 dS m−1 was applied under phosphorus-coupled nitrogen fertigation. The phosphorus-coupled nitrogen drip fertigation should be applied with cautious when applying saline water with electrical conductivity higher than 4 dS m−1. Fertigating with nitrogen fertilizers along with acid phosphate fertilizers together is a promising way to alleviate the emitter clogging caused by the ion components in saline water.

Aging of biochar-based fertilizers in soil: Effects on phosphorus pools and availability to Urochloa brizantha grass

Water-soluble phosphate fertilizers release phosphorus (P) to soils promptly, causing P fixation and low plant availability in highly weathered tropical soils. Therefore, the development of strategies to improve P use efficiency is needed. We hypothesized that biochar-based fertilizers (BBFs) can provide available P to plants and improve P use efficiency when compared with soluble fertilizers. Thus, triple superphosphate (TSP) and phosphoric acid (H3PO4) were pyrolyzed with and without magnesium oxide (MgO) and poultry litter to produce slow-release P BBFs. A pot experiment under greenhouse conditions was performed to evaluate agronomic efficiency of BBFs compared with TSP in an Oxisol. The treatments were incubated over 100 days after the application of 25, 50, 100, and 200 mg kg−1 of P. Three controls were used, including 200 mg kg−1 of P as TSP incubated for 100 days (named TSPincubation) and applied immediately before sowing (named TSPplanting) and a negative control (without P). Marandu grass (Urochloa brizantha cv. Marandu) was cultivated in pots for three cycles of 40 days each. After cultivation, a sequential extraction procedure was used to determine the P distribution among different P pools. The shoot dry matter yield in the first cropping cycle was higher at the highest P rate for TSPplanting. PLB-H3PO4-MgO showed 9% increase in the shoot dry matter when compared with TSPincubation in the first cropping cycle. In subsequent cropping cycles, all BBFs promoted higher biomass yield when compared with TSPplanting. There was an increase in the labile and moderately labile P fractions in soil after cultivation with PLB-TSP. The results suggest that BBFs can enhance P use efficiency in tropical soils in the middle- to long-term run due to slow-release profile that prevent P fixation and promote higher residual effect of fertilization.

Water soluble phosphate fertilizers for crops grown in calcareous soils – an outdated paradigm for recycled phosphorus fertilizers?

The current paradigm for phosphorus (P) fertilizers applied to calcareous soil is that almost entirely water soluble P fertilizers are efficient and sparingly soluble P fertilizers are not efficient P sources for crops. We hypothesize that this paradigm does not apply to recycled P fertilizers and that other P pools can explain the plant use of recycled P fertilizers on calcareous soil. We applied 33P isotopic dilution method to evaluate recycled P fertilizers based on plant P uptake from fertilizer relative to plant uptake from a water soluble P reference fertilizer. The predictability of fertilizer effectiveness based on sequentially extracted P forms and X-ray diffraction pattern of recycled fertilizers derived from sewage sludge, human urine and organic waste was evaluated. The plant experiments showed that tested recycled P fertilizers including compost were more effective than rock phosphate. The water insoluble P contained in urine based products was almost as effective as a fully water soluble P fertilizer. The tested recycled P fertilizers are characterized by complex P compounds differing in solubility which were so far not considered in the water and citric acid extraction methods. The fraction of resin- and NaHCO3 extractable fertilizer P explained effectiveness of P fertilizer applied to the calcareous and to an acidic soil. We concluded that water solubility is not required when P forms in recycled products are comparable to reactions products of rock phosphate based fertilizers in soil. Alternatives to fully water soluble P fertilizers are available to supply P to crops grown on calcareous soil efficiently.

Effects of Phosphorus Fertilizer Sources and Application Time on Grain Yield and Nutrient Composition of Cowpea (Vigna unguiculata L., Walp)

The appropriate time to apply water-soluble phosphate fertilizer sources for the production of cowpea (IT84E-2246-4) was evaluated in an Oxic Paleustalf at the Teaching and Research Farm, Ekiti State University, Ado-Ekiti. Cowpea growth and yield were significantly improved by single superphosphate (SSP) and triple superphosphate (TSP), each applied to supply 45 kg P2O5.ha . The increase in vegetative growth and nodulation enhanced earliness to flowering and the combined effects produced significantly higher grain yield from TSP and SSP compared to NPK 15-15-15 and the control (0kg P.ha) treatments. P fertilizer applied at sowing enhanced early vegetative growth and produced the highest number of nodules, flowers and pods.plant which ensured significantly higher grain yield than withholding the application till 3 and 5 weeks after sowing. The low grain yields obtained from application of P fertilizer at 3 and 5 weeks after sowing were not significantly different which favour applying P fertilizer at sowing time as the recommended practice. Original Research Article American Journal of Experimental Agriculture, 4(12): 1517-1525, 2014 1518

English

Phosphorus is a critical nutrient for crop production. The soil phosphorus deficit in sub-Saharan Africa is one of the most important constraints on crop productions. Resulting from the high phosphorus fixation capacities of highly weathered acidic soil coupled with the relatively low total phosphorus, the impact of this deficit is particularly pronounced in the case of rice cultivation. Phosphate rock is a promising alternative to water-soluble phosphorus fertilizers, but its low solubility has so far prevented its widespread adoption in the region. This study examined the results of a direct application effect of phosphate rock produced in Burkina Faso phosphate rock (BPR) on rice yields in on-farm trials conducted in the Guinea savannah and Equatorial forest zones, and on a phosphate rock decision support system (PRDSS) model. We initially hypothesized that BPR direct application will show little effect on rice yield due to its low solubility as same as previous studies. However, our study found that direct application of BPR has an effect on rice grain yield comparable to that of chemical water-soluble phosphate fertilizer, although according to PRDSS simulations, direct application of BPR had little effect compared to the effect of water-soluble phosphate fertilizers. The recognition of BPR effect on rice yield can enhance rice cultivation along with the aspect of usage of indigenous phosphorus resource in sub Saharan Africa (SSA).   Key words: Phosphate rock, direct application, phosphate rock decision support system (PRDSS), lowland rice, Ghana.

Phosphate amendment of metalliferous waste rocks, Century Pb–Zn mine, Australia: Laboratory and field trials

The aim of the study was to determine whether the application of phosphate compounds (phosphorite rock, phosphate fertilizer) to polyminerallic waste rocks can inhibit sulfide oxidation and metal mobility (Cu, Pb, Zn, Cd, Ni, Mn, Mg). Waste rocks comprised sulfidic carbonaceous shales and were sourced from the Century Pb–Zn mine, NW Queensland, Australia. The acid producing, Pb–Zn rich rocks consisted of major quartz, muscovite/illite, dolomite, siderite and kaolinite as well as smaller amounts of sulfide minerals (e.g. galena, sphalerite, pyrite). Laboratory leach experiments were conducted on finely granulated phosphate-treated waste rocks (>2 to <30 mm) over 13 weeks, whereas phosphate amendment of coarsely granulated waste rocks (sand to boulder size) was investigated using heap leach piles at the mine site over an 11 months period. Results of the laboratory experiments demonstrate that the treatment of finely granulated waste rocks with phosphorite rock produced leachates with near-neutral pH values due to calcite dissolution. This in turn did not allow the leaching of apatite, formation of secondary phosphate phases and phosphate stabilization to occur. Metal mobility in these amended wastes was restricted by the dissolution of calcite and the resultant near-neutral pH conditions. By contrast, the application of the water-soluble phosphate fertilizer MKP (KH2PO4) to polyminerallic sulfidic waste rocks during the short-term laboratory experiments led to the formation of phosphate coatings and precipitates and inhibited acid and metal release (Cd, Mn, Ni, Pb, Zn). At least in the short term, the application of phosphate fertilizers proved to be an effective method. However, results of the long-term field trials demonstrate that coarsely granulated waste rocks were not coated by secondary phosphate phases and that amendment by phosphorite rock or superphosphate fertilizer did not improve leachate quality compared to the unamended waste. Thus, phosphate stabilization appears ineffective in suppressing oxidation of sulfides in coarsely granulated mine wastes.

Evaluation of phosphate fertilizers for ameliorating acid mine waste

The aim of the study was to determine whether the application of bulk industrial chemicals (potassium permanganate and water-soluble phosphate fertilizer) to partly oxidized, polyminerallic mine wastes can inhibit sulfide oxidation, and metal and metalloid mobility. The acid producing waste rocks were metal (Pb, Zn, Cu) and metalloid (As, Sb) rich and consisted of major quartz, dickite, illite, and sulfide minerals (e.g., galena, chalcopyrite, tetrahedrite, sphalerite, pyrite, arsenopyrite), as well as minor to trace amounts of pre- and post-mining oxidation products (e.g., hydrated Fe, Cu, Pb, and alkali mineral salts). SEM-EDS observations of treated waste material showed that metal, metal–alkali, and alkali phosphate coatings developed on all sulfides. The abundance of phosphate phases was dependant on the fertilizer type and the availability of metal and alkali cations in solution. In turn, the release of cations was dependent on the amount of sulfide oxidation induced by KMnO 4 during the experiment and the dissolution of soluble sulfates. Mn, Ca, Fe, and Pb phosphates remained stable during H 2O 2 leaching, preventing acid generation and metal release. In contrast, the lack of complete phosphate coating on arsenopyrite allowed oxidation and leaching of As to proceed. The mobilized As did not form phosphate phases and consequently, As displayed the greatest release from the coated waste. Thus, the application of KMnO 4 and the water-soluble phosphate fertilizer Trifos (Ca(H 2PO 4) 2) to partly oxidized, polyminerallic mine wastes suppresses sulfide oxidation and is most effective in inhibiting Cu, Pb, and Zn (Sb) release. However, the technique appears ineffective in suppressing oxidation of arsenopyrite and preventing As leaching.

Phosphorus availability from phosphate rock and sewage sludge as influenced by the addition of water soluble phosphate fertilizer

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.

Agronomic evaluation of fertilizers with special reference to natural and modified phosphate rock

Most of the phosphate fertilizes currently used worldwide (16 million tonnes of P) are water soluble. Direct application of phosphate rock accounts for just 3.5%. Since most phosphate rock is used to produce water-soluble phosphate fertilizer, about 150 million tonnes of byproduct phosphogypsum are produced annually on a worldwide basis. This has given rise to concerns about its management and disposal in an environmentally acceptable manner. Despite the small amount of phosphate rock presently used for direct application, its use is becoming increasingly common in the developing countries, especially Latin America, due to the high cost of water-soluble phosphate fertilizers and to the variety of soils, crops and climatic conditions of the region. Agronomic effectiveness of phosphate rocks has been measured by the concept of Relative Agronomic Effectiveness where the yields are compared to those obtained with Triple Superphosphate (TSP) or Diammonium Phosphate (DAP). Phosphorus uptake as a response of the phosphate rock applied is measure by tissue analysis. This methodology is already ‘standard’ for the member countries of the Latin America Phosphate Rock Network.

Can acidification associated with nitrification increase available soil phosphate or reduce the rate of phosphate fixation?

It is often proposed that soil acidification by microorganisms dissolves unavailable soil phosphates, especially crystalline Ca phosphates. Unavailable phosphates, it is suggested, could thus become available to crops. Microorganisms that oxidize one ammonium ion to one nitrate ion excrete two protons into the soil solution. In the present study, this universal biological process of soil acidification was used to measure, in neutral and calcareous soils, the effect of acidification on available soil phosphate and on the rate of phosphate fixation when water-soluble phosphate fertilizers are added to soils. During nitrification the Ca2+ and Mg2+ ion concentrations in soil solutions increase but the phosphate ion concentration remains constant. The excreted protons preferentially dissolve soil Ca and Mg carbonates. Soil Ca phosphates are not dissolved; they remain unavailable. When P fertilizers were applied, the rate of fixation of phosphate ions was not slowed down by acidification associated with nitrification. This biological acidification may have a long term effect, over many years, on the slow accumulation of available phosphate in soils under native grasslands, but it cannot have a significant effect on the availability of soil P under intensive agricultural practices.

Evaluation of some sources of fertilizer phosphorus in two cycles of a paddy-wheat cropping sequence

SUMMARYA field experiment was made on Gurdaspur clay loam to assess the relative efficiency of various sources of fertilizer phosphorus for a paddy-wheat cropping sequence. Urea ammonium phosphate, superphosphate, a nitrophosphate fertilizer containing 30% water-soluble P and fertilizers containing 50 and 70% water-soluble P prepared from the nitrophosphate and superphosphate, dicalcium phosphate and rock phosphate were applied to the paddy crop at the rate of 0, 15, 30, 45 and 60 kg p2O6/ha and to wheat at double these rates.The cumulative yield data for paddy and wheat show a slight reduction in efficiency of phosphatio fertilizers, with the exception of dicalcium phosphate, as their watersoluble content decreased below 70%. In general, the relative efficiency of the less water-soluble sources and of rock phosphate was considerably higher for paddy than for wheat.The results show that the relative efficiency of low water-soluble phosphate fertilizers increased with time. The efficiency of phosphorus fertilizers declined with the rate of their application, more so in the case of higher water-soluble materials.