To Triple Superphosphate Research Articles

Loblolly Pine Mid-Rotation Phosphorus Fertilization with Poultry Litter Ash or Triple Superphosphate

ABSTRACT Loblolly pine (Pinus taeda L.) grown on infertile coastal plain soils typically shows a growth response to N and P applied at mid-rotation. The objectives of this study were to determine whether less soluble poultry litter ash (PLA) provides an adequate supply of P compared to triple superphosphate (TSP), and assess effects on P mineralization and runoff loss. Effects of 56 kg P ha−1 as either PLA or TSP, and no fertilization were compared using an 11-year-old stand of two loblolly pine genotypes on a loamy sand in a completely randomized design. Tree height, diameter and foliar nutrients, soil Mehlich 3 P and phosphatase activity (A and E horizons), and P in surface runoff were monitored. Through more than two years, P fertilization had no effect on tree growth. Similar foliar P with PLA or TSP, together with increasing foliar and soil P over time, suggested that PLA is an adequate source of P for loblolly pine. Neither fertilizer suppressed P mineralization as measured by phosphatase activity. The advantage of PLA compared to TSP is potentially much less runoff P loss.

Fate and availability of phosphorus from bone char with and without sulfur modification in soil size fractions after five-year field fertilizations

The agronomic value of fertilizer phosphorus (P) in the soil is determined by how it is incorporated and released during aggregate formation and breakdown. These processes play a vital role in P accessibility, storage, and cycling. Bone char (BC) is a promising substitute for phosphorus fertilizer. Its low P solubility can be increased by modifying the BC surface with elemental sulfur (BCplus), although the fate of BC-based P within soil aggregates have not yet been tested under field conditions. In this study, soil samples were taken from a five-year field experiment (2013–2018) to track the fate of BC and BCplus P. These samples were compared to triple superphosphate (TSP) and a control without additional P (No-P) in different soil P pools within soil aggregates in severely P deficient vs. sufficiently P fertilized Cambisol. Soil aggregate distributions were assessed after wet-sieving, centrifugation, and tangential flow filtration to separate small macroaggregates (250–2000 µm, SMaA), large microaggregates (53–250 µm, LMiA), small microaggregates (1–53 µm, SMiA), and composite building units (< 1 µm, BU). Soil P status was assessed after sequential extraction (Hedley scheme). We found that the mass proportions of soil size fractions decreased in the order of SMiA > LMiA ≈ SMaA > BU. The addition of 45 kg P ha−1 year−1 using different fertilizers significantly increased the mass proportion of LMiA from 7% to 22% in comparison to the No-P. This was likely due to stimulated plant growth after fertilization and thus introduction of organic binding agents which increased soil aggregation. The addition of BC and BCplus showed nearly no significant effect when compared to No-P on soil P pools. However, sulfur modification of BC resulted in higher labile P which was comparable to that found in TSP. Therefore, we conclude that BCplus behaves similarly to TSP, without any additional positive or detrimental effects on P status. This lends support for the use of BC wastes as a possible substitute for TSP, which would represent a move towards more sustainable agriculture with more closed P cycles.

Increasing phosphorus fertilizer value of recycled iron phosphates by prolonged flooding and organic matter addition

Iron (Fe) minerals are commonly used to remove phosphorus (P) from waste streams, producing P-loaded Fe(III) oxides or Fe(II) phosphate minerals (e.g., vivianite). These minerals may be used as fertilizers to enhance P circularity if solubilized in soil. Here, we tested the P fertilizer value of recycled Fe phosphates (FePs) in a pot trial and in an incubation experiment, hypothesizing that P release from FePs is possible under Fe(III)-reducing conditions. First, a pot trial was set up with rice (Oryza sativa) in all combinations of soil flooding or not, three P-deficient soils (acid, neutral, and calcareous), and six FePs (three Fe(III)Ps and three Fe(II)Ps) referenced to triple superphosphate (TSP) or zero amendments. Shoot P uptake responded to TSP application in all treatments but only marginally to FePs. The redox potential did not decrease to -200 mV by flooding for a brief period (13 d) during the pot trial. A longer incubation experiment (60 d) was performed, including a treatment of glutamate addition to stimulate reductive conditions, and P availability was assessed with CaCl2 extraction of soils. Glutamate addition and/or longer incubation lowered soil redox potential to < -100 mV. On the longer term, Fe(III) minerals released P, and adequate P was reached in the calcareous soil and in the neutral soil amended with Fe(III)P-sludge. It can be concluded that prolonged soil flooding and organic matter addition can enhance the P fertilizer efficiency of FePs. Additionally, application of FeP in powder form may enhance P availability.

Preferences of Pinus sylvestris seedling roots for different phosphorus sources under phosphorus-deficient conditions

PurposePhosphorus (P) is a limiting nutrient in many managed forests. To further understand the risks and benefits of biochars as sustainable P source in forest management, an improved mechanistic understanding of its interactions in root systems is required.MethodsA rhizobox experiment was conducted to observe root response of P. sylvestris (Scots pine) seedlings to different biochars in comparison to triple superphosphate (TSP) fertiliser as a P source. Three types of wood-derived biochar were compared: biochar from mixed softwood pellets (“Reference biochar”); from the vascular cambium zone of Picea sitchensis (“VCZ biochar”) and from mixed softwood pellets infused with TSP (“Processed biochar”). These biochars presented a range of available P from low to high. Seedling root development was spatially analysed using GIS software.ResultsThe total length of P. sylvestris roots did not significantly differ between treatments. However, seedling roots showed strong preference for soil proximal to VCZ biochar and strong avoidance to TSP fertiliser. There was a milder avoidance effect for Processed biochar. Differences in root responses could be explained by available P: roots favored a moderate, sustained P source and avoided high available P sources. The avoidance effect can be attributed partially to lower soil pH around TSP fertiliser.ConclusionThe extent concentration and duration of P availability affects the root response of P. sylverstris to P sources. Under P-deficient conditions, P. sylvestris root growth was markedly improved by introducing biochar with a certain P concentration, and VCZ biochar has potential as an effective source of P in forest establishment.

Phosphorus solubility and dynamics in a tropical soil under sources derived from wastewater and sewage sludge

Conventional phosphate fertilizers are usually highly water-soluble and rapidly solubilize when moistened by the soil solution. However, if this solubilization is not in alignment with plants demand, P can react with the soil colloidal phase, becoming less available over time. This is more pronounced in acidic, oxidic tropical soils, with high P adsorption capacity, reducing the efficiency of P fertilization. Furthermore, these fertilizers are derived from phosphate rock, a non-renewable resource, generating an environmental impact. To assess these concerns, waste-recycled P sources (struvite, hazenite and AshDec®) were studied for their potential of reducing P fixation by the soil and improving the agronomic efficiency of the P fertilization. In our work, we compared the solubilization dynamics of struvite, hazenite, AshDec® to triple superphosphate (TSP) in a sandy clay loam Ferralsol, as well as their effect on solution pH and on soil P pools (labile, moderately-labile and non-labile) via an incubation experiment. Leaching columns containing 50 g of soil with surface application of 100 mg per column (mg col−1) of P from each selected fertilizer and one control (nil-P) were evaluated for 60 days. Daily leachate samples from the column were analyzed for P content and pH. Soil was stratified in the end and submitted to P fractionation. All results were analyzed considering p < 0.05. Our findings showed that TSP and struvite promoted an acid P release reaction (reaching pHs of 4.3 and 5.5 respectively), while AshDec® and hazenite reaction was alkaline (reaching pHs of 8.4 and 8.5 respectively). Furthermore, TSP promoted the highest P release among all sources in 60 days (52.8 mg col−1) and showed rapid release dynamic in the beginning, while struvite and hazenite showed late release dynamics and lower total leached P (29.7 and 15.5 mg col−1 P respectively). In contrast, no P-release was detected in the leachate of the AshDec® over the whole trial period. Struvite promoted the highest soil labile P concentration (7938 mg kg−1), followed by hazenite (5877 mg kg−1) and AshDec® (4468 mg kg−1), all higher than TSP (3821 mg kg−1), while AshDec® showed high moderately-labile P (9214 mg kg−1), reaffirming its delayed release potential.

Efficiency of Recycled Biogas Digestates as Phosphorus Fertilizers for Maize

Despite phosphorus resources on Earth being limited, over fertilization in many agricultural situations causes significant resource consumption. Phosphorus-recycling within agricultural production can reduce global dilution into the environment and is thus essential to secure sustainable future supply. This study investigated the fertilization efficacy of phosphorus fertilizers recycled from biogas digestates in maize shoots grown under controlled greenhouse conditions, in two soils, in a pot experiment. Variables investigated were plant-available phosphorus in soil, plant biomass production, and concentration of phosphorus, calcium, and magnesium in shoots. Soils were treated with three different fertilizer fractions, separated from biogas digestates, at equivalent phosphorus concentrations, using different combinations and application techniques, isolated or in combination, and compared to triple superphosphate (TSP) as a reference. One of the fractions (P-Salt) had effects on biomass production and plant phosphorus concentration equivalent to TSP in agricultural surface soil. In the second soil (with less active soil life and nutrient content), equivalence to TSP was achieved with combinations of two recycled fractions (P-Salt and dried solids). The enhancement of the phosphorus fertilizing effect by the solids was synergistic, indicating that the solids had a soil conditioning effect. The results show that biogas digestates are a valuable source for phosphorus recycling of fractions that have equivalent or even superior fertilizing properties compared to TSP.

Growth and elemental uptake of Rhodes grass (Chloris gayana) grown in a mine waste-contaminated soil amended with fly ash-enriched vermicompost.

Vegetation cover in mine waste-affected soils is necessary to ensure sustainability of these fragile ecosystems. This study evaluated the potential of fly ash-enriched vermicompost (FV) to improve growth of Chloris gayana in a gold mine waste-affected soil. The treatments in the study were based on optimizing phosphorus supplied as vermicompost at 20mg P and 40mg P per kilogram soil which were compared to triple super phosphate (TSP) applied at 40mg P/kg. The 40-mg P/kg FV treatment resulted in 38.4%, 164% and 182.5% significant increase in shoot height, shoot biomass and root biomass, respectively, relative to the control. The increased biomass was reflected in the plant tissue analysis where 40mg P/kg FV had high P, Ca, Mg and K, though not significantly different to the 20-mg P/kg FV treatment. Amendment effect had no influence on plant tissue N, Pb, Cd and As. Chloris gayana uptake of Fe, Mn, Zn and Cr was significantly reduced with addition of the vermicompost, whereas Cu and B were significantly increased in the 40-mg P/kg FV treatment relative to the control though the increases did not exceed the critical concentration limits of these elements. Therefore, re-vegetation of mine waste-contaminated soils can be achieved with addition of FV at a rate of 40mg P/kg FV. However, more studies may need to be done under field conditions to further evaluate the effectiveness of such vermicomposts in improving the re-vegetation capacity of mine waste-contaminated soils.

Algal biomass from wastewater: soil phosphorus bioavailability and plants productivity

The cultivation of microalgae in wastewater allows to obtain a biomass concentrated in nutrients and organic material. This biomass added to phosphate fertilizers can promote a slow release of the nutrient and consequently a higher absorption of phosphorus (P). The objective of this study was to investigate P uptake by plants subjected to triple superphosphate (TSP) fertilization, added with microalgae biomass (MB) grown in wastewater. TSP was added with different MB proportions in order to verify if there would be a different behaviour in P release for millet (Pennisetum glaucum L.) plants. With the proportion that maximized P accumulation in plants, a second experiment was carried out to investigate whether MB exerts influence of P diffusion in the soil. Finally, a third trial was conducted in a greenhouse, where TSP and TSP + 12% MB were applied to the soil under different phosphorus doses in corn (Zea mays L.). The proportion of MB in TSP that maximized the increase of P content and concentration in plants was approximately 12% MB. From this proportion, a reduction in the values of the variables analysed in the plant with the increase of the proportion of MB in the biofertilizer was observed. Similar behaviour was observed when evaluating P diffusion in sandy and clay soils. Fertilizers TSP and TSP + 12% MB showed no difference in P diffusion in the soil, while the ratio of 30% MB clearly impaired P diffusion. In a greenhouse, the P content presented significant difference for the tests carried out with TSP and TSP + 12% MB fertilizer, in which the latter provided higher P recovery rate by plants. Therefore, MB added to TSP had a positive influence on plant development and its P recovery capacity when applied in a proportion of 12% MB to the fertilizer mass.

Agronomic effectiveness of a granular poultry litter-derived organomineral phosphate fertilizer in tropical soils: Soil phosphorus fractionation and plant responses

Production of organomineral phosphate fertilizers (OMF) from poultry litter (PL) has been suggested to reduce the dependence on phosphorus (P) reserves. Here, we compared a granular PL-derived OMF to triple superphosphate (TSP) in two contrasting tropical soils (Oxisol and Entisol) by using isotope dilution with 32P. Our study aimed to gain insight into soil P fractionation, and P availability to maize plants achieved by P fertilization (0, 25, 50, 75 and 100 mg kg−1 of soil), in order to investigate the agronomic effectiveness of OMF. Despite μ-XRF maps revealing that the mixture of PL and TSP as OMF resulted in P hot spots disseminated in a low-concentration background, whereas for the TSP treatment higher P concentration was uniformly distributed in the granules, there was no difference in maize yield and fertilizer P recovery (%R) between P sources in both soils. In the Oxisol, there was no difference between fertilizers in any of the soil P pools, but larger readily phytoavailable P and smaller moderately labile P fractions were obtained with OMF. In the Entisol, the labile P pool was larger with TSP. Nevertheless, acid and alkaline phosphatase activity and microbial biomass were affected by P rate and P source. The results show that OMF is an effective substitute for conventional phosphate fertilizers, since OMF promotes P recovery, plant P uptake and biomass yields compared to those obtained with TSP.

Response of Rapeseed (Brassica napus L.) and Phosphorus Fractionation in an Alkaline Soil Amended with Rock Phosphate and Elemental Sulphur

A field experiment was conducted to investigate the response of rapeseed (Brassica napus L.) to application of Syrian rock phosphate (RP) mixed with three rates of elemental sulphur (10, 20 and 50% S) in an alkaline calcareous soil compared to triple superphosphate (TSP). The RP was applied @ 800 mg P kg−1 soil. The transformations of various pools of phosphorus (P) were also studied after the harvest of rapeseed grown for two consecutive seasons. The P fractionation scheme divided calcium phosphate into three types namely, dicalcium phosphates (Ca2-P), octacalcium phosphates (Ca8-P) and apatite (Ca10-P). The results showed that rapeseed plant utilized P from Syrian RP as good as that of TSP in both seasons. Mixing of elemental S with RP showed no effects on dry matter yield in first season, whereas in the second season, all mixing rates of S increased dry matter production significantly. Mixing of RP with S influenced RP dissolution, thereby all inorganic P (Pi) fractions increased. The dominant P fractions in RP and RP+S treatments were Ca10-P, followed by Ca8-P. The opposite was true for TSP treatment. The Ca2-P was the main source of available soil P as it correlates significantly with Olsen-P.

Phosphorus effects of recycled products from municipal wastewater on crops in a field experiment

In this study, the phosphorus (P) fertilizing effects of struvite, one thermochemical-treated sewage sludge ash (SSA) based on Ca-P (Ca-SSA) and one full sulfuric acid-digested SSA based on Al-P (Al-SSA) were analysed in comparison to triple superphosphate (TSP) and a control treatment (CON) without P application in a two-year field experiment. In the field experiment, the effects of the recycling products on crop yield, P uptake and labile soil P fractions were analysed. In addition, the effect of nitrogen and magnesium contained in struvite was investigated in the second year of the experiment compared to TSP and CON. In the first year, spring barley was cultivated in the field experiment; and in the second year, it was forage rye followed by sorghum. In the second year, the relative P effectiveness (forage rye, sorghum) of the recycling products compared to TSP increased in the order: Ca-SSA (81%, 91%) ≤ Al-SSA (91%, 96%) = struvite (102%, 110%). In addition, an magnesium fertilizing effect of struvite could be demonstrated. The results show that the recycling products from wastewater treatment are appropriate to substitute rock phosphate-based fertilizers.

High plant availability of phosphorus and low availability of cadmium in four biomass combustion ashes

For biomass combustion to become a sustainable energy production system, it is crucial to minimise landfill of biomass ashes, to recycle the nutrients and to minimise the undesirable impact of hazardous substances in the ash. In order to test the plant availability of phosphorus (P) and cadmium (Cd) in four biomass ashes, we conducted two pot experiments on a P-depleted soil and one mini-plot field experiment on a soil with adequate P status. Test plants were spring barley and Italian ryegrass. Ash applications were compared to triple superphosphate (TSP) and a control without P application. Both TSP and ash significantly increased crop yields and P uptake on the P-depleted soil. In contrast, on the adequate-P soil, the barley yield showed little response to soil amendment, even at 300–500kgPha−1 application, although the barley took up more P at higher applications. The apparent P use efficiency of the additive was 20% in ryegrass - much higher than that of barley for which P use efficiencies varied on the two soils. Generally, crop Cd concentrations were little affected by the increasing and high applications of ash, except for relatively high Cd concentrations in barley after applying 25Mgha−1 straw ash. Contrarily, even modest increases in the TSP application markedly increased Cd uptake in plants. This might be explained by the low Cd solubility in the ash or by the reduced Cd availability due to the liming effect of ash. High concentrations of resin-extractable P (available P) in the ash-amended soil after harvest indicate that the ash may also contribute to P availability for the following crops. In conclusion, the biomass ashes in this study had P availability similar to the TSP fertiliser and did not contaminate the crop with Cd during the first year.

Eficiência do fosfato natural de Gafsa associado à calagem e gesso e sintomas nutricionais da alfafa, &lt;em&gt;Medicago sativa&lt;/em&gt; L.

This experiment was carried out in glasshouse, Alfalfa, Medicago sativa L. (Poaceae), was cultivated in Typical Mapluolox soil. The study aimed at evaluating the agronomic efficiency index (AEI) of Gafsa phosphate (GP) and of GP with gypsum application before and after liming compared to triple superphosphate (TS), at the rates of 50, 100 and 200 mg P dm -3 , as well as relating soil nutrients with the treatments and with the nutrient symptoms. Three sowings were made. All GP combinations presented a very low AEI during the first sowing and high in third sowing. A higher soil phosphorus concentration was obtained with GP than TS only after ultimate harvest. Liming before or after phosphate fertilization had similar responses on soil phosphorus concentration. Phosphorus deficiency occasioned reduced growth and purple stem. Symptoms of manganese toxicity were characterized by a yellow and purple color in the leave borders. The efficiency of GP increased with the time.

Frações de fósforo em estrumes e sua eficiência como adubo fosfatado

Os estrumes empregados como fontes de fósforo podem ter eficiência fertilizante diferente da dos adubos comerciais solúveis. Tal eficiência pode variar com a origem do estrume e com as proporções das diferentes frações químicas do P total contido. A eficiência de estrumes de frangos de corte e de bovinos de leite, relativamente ao superfosfato triplo-ST, e a correlação desta eficiência com frações de fósforo contidas nestes materiais foram estimadas em experimento de casa de vegetação. Os tratamentos aplicados foram: um controle, sem P; as doses 6,6, 13,2 e 19,7 mg kg-1 de P de ST, e uma dose única de 15,3 mg kg-1 de P de 11 amostras de cada um dos dois tipos de estrumes. Utilizou-se um Podzólico Vermelho-Escuro e a resposta aos tratamentos foi determinada com o cultivo de milheto (Pennisetum americanum) durante 27 dias, a partir da adubação fosfatada, período em que foram colhidos três cortes de plantas. As frações de fósforo dos estrumes foram determinadas por extrações seqüenciais. O índice de eficiência (IE), estimado pelo método de equivalentes em ST, dos estrumes de frango foi de 0,84 ± 0,071, valor menor do que o dos estrumes de bovinos de leite, de 0,94 ± 0,095. Não ocorreu diferença de IE entre as amostras de estrumes de mesma espécie animal. Considerando todas as amostras, o IE apresentou correlação positiva com as proporções de P lábil, extraídas por resina trocadora de ânions e NaHCO3 0,5 mol L-1, e de P inorgânico total e correlação negativa com as proporções de P extraídas por NaOH 0,1 mol L-1 e HCl 0,5 mol L-1 e de P orgânico total. Não ocorreu correlação entre o IE e o teor total de P dos estrumes.

Agronomic evaluation of unacidulated and partially acidulated Minjingu and Chilembwe phosphate rocks for clover production in Ethiopia

Most soils in sub-Saharan Africa are P deficient, but the high cost of water-soluble P fertilizers limits the use of P fertilizers by resource-poor farmers. A low-cost alternative is to apply phosphate rocks. We evaluated the effectiveness of unacidulated (PR), 25% partially acidulated (PAPR25), and 50% partially acidulated (PAPR50) Minjingu and Chilembwe phosphate rocks relative to triple superphosphate (TSP) on Trifolium quartinianum grown on a Vertisol in the Ethiopian highlands. The fertilizers were applied once at 0–80 kg P ha −1 and their effects were followed in four consecutive clover crops. In the Minjingu phosphate rock experiment, clover DM yields without applied P were below 1 t DM ha −1 in all except the first of four consecutive crops. With P application, herbage yields reached as high as 14 t ha −1. Significant ( P<0.05) effects of P on clover DM and P uptake were observed at least up to crop 3. Over all the four crops, PR was 114%, PAPR25 was 113% and PAPR50 was 107% as effective as TSP in increasing clover herbage yields. The corresponding relative responses in P uptake were: 128, 121 and 112% for PR, PAPR25 and PAPR50, respectively. The substitution rates in herbage yields were: 130% for PR, 128% for PAPR25 and 114% for PAPR50 while those for P uptake were 164% for PR, 146% for PAPR25 and 125% for PAPR50. In the Chilembwe phosphate rock experiment, clover DM yields without applied P were below 1.3 t DM ha −1 in the five years of the study. With P application, herbage yields reached as high as 7 t ha −1. Significant effects of P on clover DM and P uptake were observed only in the first two crops. Over all the five crops, PR was 27%, PAPR25 was 57% and PAPR50 was 73% as effective as TSP in increasing clover herbage yields. The corresponding relative responses in P uptake were 18, 49 and 59% for PR, PAPR25 and PAPR50, respectively. The substitution rates in herbage yields were 7% for PR, 32% for PAPR25 and 53% for PAPR50 while those for P uptake were 3% for PR, 24% for PAPR25 and 35% for PAPR50. It was concluded that raw Minjingu phosphate rock is highly effective on clover in these Vertisols and partial acidulation is not necessary, but raw Chilembwe phosphate rock is ineffective and 50% partial acidulation is recommended.

Agronomic effectiveness and residual effects of Egyptian and Togo phosphate rocks on clover production

The high cost of conventional, water‐soluble phosphorus (P) fertilizers limits their use by resource‐poor farmers in sub‐Saharan Africa. Phosphate rocks are a low‐cost alternative. We evaluated the effectiveness and residual effects of Egyptian phosphate rock (EPR) and Togo phosphate rock (TPR) relative to triple superphosphate (TSP) applied at 0, 20, 40, 80, and 160 kg P ha‐1 to annual Trifolium species grown in a P‐deficient Vertisol. The fertilizers were applied once and their effects were followed on seven consecutive annual clover crops. Clover responded to P at all the rates used. Significant (P<0.05) responses to P at the low 20–40 kg P ha‐1 rates were registered up to the fifth crop after application of P, and responses to higher rates of 80–160 kg P ha‐1 were significant up to the seventh crop. Critical evaluation of residual effects by comparing the response of clover to these fertilizers with response to fresh applications of TSP in the second and third crops confirmed these observations. Over all the seven crops, EPR was 82% as effective as TSP in increasing clover DM and 83% as effective in increasing P uptake. Its substitution rates were 67% for DM yields and 69% for P uptake. For TPR, the relative responses were 54% and 52% for DM yield and P uptake, respectively, and the corresponding substitution rates were 29% and 27%. In separate experiments, the effects of mixing these phosphate rocks with triple superphosphate (TSP) in various proportions (at 60 kg P ha‐1) were also investigated. The highest response of clover was observed with TSP applied alone, but the phosphate rocks applied alone also significantly increased yields compared with the controls without applied P. Mixtures of TPR and TSP increased yields only slightly over pure TPR, and mixtures of EPR and TSP had no effect on yields compared with pure EPR, presumably because EPR is more reactive than TPR. It was concluded that EPR is highly effective in these soils, but the effectiveness of TPR is low. The highly reactive EPR could be used to elevate the P status of the P‐deficient Vertisols and increase feed availability and livestock productivity in the Ethiopian highlands. Mixing of these phosphate rocks with TSP cannot be recommended.

Effectiveness of Egyptian phosphate rock on clover production in Ethiopia1

The majority of soils in Africa are phosphorus (P) deficient, but the high cost of water‐soluble P fertilizers limits their use by resource‐poor farmers. A low‐cost alternative is to use phosphate rocks. We evaluated the effectiveness of Egyptian phosphate rock (EPR) relative to triple superphosphate (TSP) applied at 0, 15, 30, 45, and 60 kg P ha‐1 to annual Trifolium species grown on a P‐deficient Vertisol. The fertilizers were applied once and their effects were followed on seven consecutive annual clover crops. Clover responded to P at all the rates used. Significant (P<0.05) P effects on clover P content and DM yields were observed up to the fourth crop. Over all the seven crops, EPR was 89% as effective as TSP in increasing herbage DM and 93% as effective in increasing herbage P content. Its substitution rates were 79% for DM yield and 86% for clover P content. Therefore, EPR was highly reactive and its use could elevate the P status of the P‐deficient Vertisols and increase feed and livestock productivity in the Ethiopian highlands.

The agronomic effectiveness of reactive phosphate rocks 4. Early season lag in herbage production when reactive phosphate rock is used as a pasture fertiliser

Summary. The agronomic effectiveness of highly reactive North Carolina phosphate rock (NCPR), relative to triple superphosphate (TSP), was determined for individual harvests at 26 permanent pasture sites in the National Reactive Phosphate Rock Project from 1992 to 1995. The aim was to determine whether the performance of NCPR relative to TSP was consistent over the growing season. Poor performance of NCPR early in the growing season (early seasonal lags), and its subsequent improvement later in the season, was observed at 15 of the 26 sites in this project and for 20 of the 103 possible site x year combinations. At 3 additional sites the apparent early season lag in NCPR performance was followed by harvests where there was no phosphorus (P) response. At one P-leaching site with a long growing season the relative yields from NCPR plots increased as the year progressed and exceeded those from TSP late in th e season. The duration of the early season lag phase was associated with the rate of build-up in plant-available P over the 4-year duration of the trials. The lag disappeared after 1 or 2 years at sites with low P-sorbing, sandy soils where there was a significant build-up in Colwell P, but persisted for 4 years on high P-sorbing soils where limited increases in Colwell P occurred. The average early season yield reduction associated with use of NCPR, compared with using TSP, was 28%. Colwell soil test values alone did not provide a good indication of the likelihood of a seasonal effect occurring. The occurrence of an early season lag phase needs to be taken into account by farmers considering the use of RPR as reductions in feed supply at this time of the year have the potential to reduce stocking rates and farm profitability. The use of partially acidulated NCPR, or large applications of NCPR applied in the first year, were management strategies that minimised the occurrence of these seasonal effects. The suggestion that the early season lag effect is due to the inability of NCPR to meet P demands from newly establishing pasture legumes, and increased P requirements by pasture plants in cold conditions is also discussed.

Iron and Aluminum Oxide Influence on Agronomic Effectiveness of Modified Phosphate Rocks

AbstractA greenhouse experiment was conducted to study the influence of Fe and Al oxide in phosphate rocks (PR) on partially acidulated phosphate rock (PAPR) effectiveness and to evaluate compaction of PR with soluble phosphates as an alternate method of utilizing PR with high Fe and Al oxide. Five PR with Fe + Al oxide ranging from 19 to 320 g kg−1 were acidulated with 50% of the H2SO4 (PAPR, 50% H2SO4) required to fully convert the PR to triple superphosphate (TSP) or were compacted with TSP so that 50% of the total P was in TSP form (PR + TSP). They were applied to Hartsells silt loam (fine‐loamy, siliceous, thermic Typic Hapludult, pH 4.8) at rates 50, 100, 200, and 300 mg P kg−1. Two successive crops of maize (Zea mays L.) and one of rice (Oryza sativa L.) were grown. Biomass yield of the first crop from PAPR‐treated soils decreased from 86% of that from TSP to 16% and P uptake from 72 to 12% with increasing Fe and Al oxide from 1.9 to 32%. The decrease in effectiveness of PAPR was directly related to a decrease in water‐soluble P in PAPR with increasing Fe and Al oxide content. The compacted PR = TSP were 86 to 104% as effective as TSP in increasing biomass yield and 78 to 94% as effective in increasing P uptake. There were no great differences between PAPR and the compacted PR + TSP in terms of residual effect on the second crop of maize, except for Matongo PR. The difference in residual effectiveness between PAPR and compacted PR + TSP was not as pronounced for rice as for maize.

Residual effectiveness of superphosphate is greater than that of rock phosphate fertilisers for lateritic soils in south-western Australia

The residual values of granular reactive rock phosphate (highly carbonate-substituted apatite from North Carolina, USA.), partially powdered low-reactive Queensland rock phosphate (low carbonate-substituted apatite from the Duchess deposit), and granular triple superphosphate were measured in 3 experiments on different lateritic soils in different climatic regions of south-western Australia (Gibson, South Bodallin, West Dale). Finely powdered calcined crandallite-millisite rock phosphate from Christmas Island (Calciphos) was included in one of the experiments. The fertilisers were applied once only in May 1984 and their residual value measured over 3 years (1984-1986) using yield and phosphorus content of the following species each year: experiment 1 (Gibson), barley in years 1 and 2 and oats in the third year; experiment 2 (South Bodallin), triticale in all 3 years; experiment 3 (West Dale), subterranean clover in years I and 2 followed by oats in year 3. Relative to triple superphosphate (TSP) applied each year, the effectiveness of superphosphate in year 1 (year of application) in the experiment at Gibson decreased by about 40% between years 1 and 2, and by a further 5% between years 2 and 3. The corresponding values for the experiment at South Bodallin were 75% and 5%, and at West Dale 50% and 25%. All rock phosphates were much less effective than TSP in year 1, being 5-30% as effective as TSP. Effectiveness of rock phosphates remained low over the 3 years, being 5-20% as effective as newly applied TSP. Although the effectiveness of TSP decreased, it continued to be 50% as effective as newly applied TSP after 3 years. Residual TSP and both freshly applied and residual rock phosphates did not support the same maximum yield as freshly applied TSP despite well defined yield plateaux being obtained in each case. At each harvest, the relationship between yield and phosphorus content of plants was similar for all fertilisers so that the smaller maximum DM and grain yield and reduced effectiveness of the rock phosphates were largely due to less phosphorus being taken up by plants.