Christmas Island Rock Phosphate Research Articles

Water use efficiency, plant growth and vegetative traits of rubber (Hevea brasiliensis) seedlings grown using different growing media and water levels

The aim of this study was to evaluate the effects of soilless media and water levels on growth and physiological response of rubber plant. The four water levels were I50: 50%, I75: 75%, I100: 100% and I150: 150%) with three replications per water treatment and four soilless media. Water levels were determined as irrigation needed for the root zone in growing media to rise to field capacity I100:100%, at field capacity (FC). The experiment was laid out in randomized complete block design (RCBD) in factorial arrangement 3 x 4 with three replications. Soilless medium contains proportion of vermiculite, perlite, coconut husk, empty fruit bunch (EFB) compose, Christmas Island Rock Phosphate (CIRP), peat moss, urea-N and burnt rice husk coded as M1. Vermiculite, perlite, coconut husk, EFB, CIRP, peat moss, urea-N, sugarcane bagasse coded as M2. M3 is a commercial soilless medium and 100% soil was designated as control. The M1 significantly influenced almost all plant growth traits, noticeable in biomass production. Growth of plants in M1 corresponded to higher water use efficiency WUEinstantaneous and WUEintrinsic, the M1 increased plant growth like LAR, biomass production and root morphological traits. Shoot dry weight of the plant was greater (14.66 g/plant) when 150% was applied and significantly different from M2 (10.36 g/plant), M3 (4.73 g/plant) and M4 6.22 g/plant. Lower water level 50%, applied in plant grown in M1 (31.94 g/plant) recorded highest total shoot fresh weight (SFW). The results showed suitability of the soilless medium M1 and the 50% water level for rubber nursery planting. Consequently, it is recommended for planting where management and control of irrigation water are considered necessary in rubber plantation.

Effects of Amending Phosphatic Fertilizers with Clinoptilolite Zeolite on Phosphorus Availability and Its Fractionation in an Acid Soil

Soils of the tropics are highly weathered, acidic, and low in phosphorus (P) because of high contents of Al and Fe. Satisfactory P supply is essential to ensure optimum soil and crop productivity. Thus, there is a need for amending soils with zeolite to improve availability of P in acid soils as this mineral can fix Fe and Al instead of P. This study was undertaken to determine the transformations of P fertilizers in acid soils following application of Clinoptilolite zeolite (CZ) in laboratory (incubation) and pot trials. An acid soil was incubated with a recommended fertilization rate and a reduced amount of the existing recommended fertilization by 25% but substituting this reduction with an equivalent amount of CZ. Triple superphosphate (TSP), Egypt Rock phosphate (ERP), and Christmas Island Rock phosphate (CIRP) were used as P sources. Selected soil chemical properties, inorganic P fractions, available P, and total P of the native soil were determined before and after the laboratory and pot trials. Zea mays L. (test crop) plant dry matter production, P concentration, P uptake, and P use efficiency were also determined using standard procedures. Effects of the treatments with CZ compared to the recommended fertilization on P fixation were similar. In the laboratory study, the treatments with TSP showed lower dominance of Fe–P but more pronounced in Al–P, whereas for the RPs, Ca–P was dominant. In the pot study, Al–P, Ca–P, and Fe–P were rather pronounced in the treatments with TSP, ERP, and CIRP, respectively. There was a decrease in exchangeable Al and soil titratable acidity because of the ability of the CZ to increase soil pH. Although the availability of P was not significant with the inclusion of CZ in the incubation study, dry matter production, P concentration, P uptake, and P use efficiency in the pot trial were comparable with that of the existing/recommended fertilization, suggesting that the CZ is beneficial and could be used to reduce the P fertilizer requirement for Zea mays L. cultivation on acid soils. Regardless of type of P fertilizer, prevalence of the moderately labile P fractions (Al–P, Fe–P, and Ca–P) of the incubation and pot studies acted as slow-release P sources to contribute to long-term P release. Further studies on the potential of CZ to reduce fertilization and its effects on soil and crop productivity are essential. It is also important to determine the economic benefits of including CZ in Zea mays L. cultivation.

Effect of Christmas Island rock phosphate and rice straw compost application on soil phosphorus availability and maize (Zea maysL.) growth in a tropical acid soil of Kelantan, Malaysia

AbstractPhosphorus (P) fixation is very common in Malaysian acid soils due to the fixation of soluble inorganic P by Al and Fe under acidic soil pH conditions. Farmers tend to perform lots of liming and apply excess amount of P fertilizers in order to saturate the Al and Fe in the soil so that the plants are able to absorb the remaining P. Excessive liming and application of P fertilizers are not only not economical but also not environmentally friendly. Compost with a large surface area and pool of negative charges could be used to reduce P fixation in acidic soil. Hence, this study was carried out to assess the effect of amending Christmas Island rock phosphate (CIRP) with rice straw (RS) compost in improving soil P availability, nutrient uptake, and dry matter production of maize cultivated on a Malaysian tropical acid soil. A pot experiment was carried out in this study with the use of maize (FI hybrid sweet corn 801) as a test crop. The chemical properties of soils applied with RS compost were significantly improved (P≤ 0.05) compared to treatments without RS compost. As the soil pH increased, there was significant reduction in exchangeable acidity, Al and Fe in soil due to exchangeable Al and Fe were fixed with negatively charged functional groups of RS compost’s surfaces, thus increased the P availability and exchangeable cations in the soil applied with RS compost. There was also significantly higher N, P, and K uptake in leaf, stem, and root of maize in the treatments applied with RS compost. Application of CIRP with RS compost was found to increase the soil P availability, maize nutrient uptake, and dry matter production at the end of the pot experiment. An application rate of 15–20 t ha−1of RS compost together with 130 kg ha−1urea, 200 kg ha−1CIRP, and 67 kg ha−1muriate of potash is recommended to improve the soil NPK contents and growth ofZea maysin acidic soil.

Performance of Bambara groundnut (Vigna subterranea L. Verdc.) with rice husk biochar and Christmas Island Rock Phosphate application

PurposeBiochar application could be a sustainable way to enhance the nitrogen fixation in Bambara groundnut and other legumes. The research was conducted to study the effect of rice husk biochar and the Christmas Island Rock Phosphate application on the performance of Bambara groundnut in the study area.MethodsTwo levels of rice husk biochar (0 and 10 t/ha) and four levels of Christmas Island Rock Phosphate (0, 20, 40 and 60 kg P2O5/ha) were factorially combined to make a total of eight treatment combinations which were laid out in a randomized complete block design (RCBD) with three replicates. Data were collected on nitrogen content and fixation of the crop.ResultsApplication of rice husk biochar increased the total mean of nitrogen content and N fixed by the crop from 120.0 and 90.9 kg/ha to 147.6 and 114.1 kg/ha, respectively. However, the effect of rock phosphate application on the nitrogen content and fixation of the crop was not observed.ConclusionRice husk biochar application at 10 t/ha alone was sufficient for nitrogen content and fixation of the crop. This implies that farmers in the study area can apply rice husk biochar at 10 t/ha to enhance the performance of the crop.

Amending inorganic fertilizers with rice straw compost to improve soil nutrients availability, nutrients uptake, and dry matter production of maize (<em>Zea mays</em> L.) cultivated on a tropical acid soil

This study was carried out to assess the effect of amending inorganic fertilizers with rice straw (RS) compost in improving the soil nutrients availability, nutrient uptake, and dry matter production of maize cultivated on a tropical acid soil. A pot trial was conducted for 60 days and maize (F1 hybrid sweet corn 801 variety) was used as a test crop. Rice straw compost was applied at rates of 5 t ha-1, 10 t ha-1, 15 t ha-1 and 20 t ha-1, respectively. Treatments of amending inorganic fertilizers with RS compost were found to increase soil total N, available P, and exchangeable K at the end of the pot experiment. This was possible because it increases the nutrients availability in the tropical acid soil by reducing NH3, H2PO-, and K+ loss through volatilisation, leaching and denitrification. The soil pH and the soil EC also significantly increased with the presence of RS compost. Dry weight of maize plants (leaf and stem) and higher N, P, and K uptake in leaf, stem, and root of maize were observed under treatments amended with RS compost. An application rate of 15–20 t ha-1 of RS compost together with 130 kg ha-1 urea, 200 kg ha-1 Christmas Island rock phosphate, and 67 kg ha-1 muriate of potash are recommended to improve the soil NPK contents and growth of Zea mays in acidic soil.

Effects of clinoptilolite zeolite on phosphorus dynamics and yield of Zea Mays L. cultivated on an acid soil.

Efficient management of P fertilizers ensures good yield of crops and adequate food supply. In the acid soil of the tropics, soluble P is fixed by Al and Fe. Exploitation of the high CEC and pH of Clinoptilolite zeolite (CZ) could mitigate low soil pH and P fixation in acid soils. This study was undertaken to determine the effects of amending a weathered acid soil with CZ on: (i) soil P availability and other related soil chemical properties, and (ii) nutrient concentration, nutrient uptake, above-ground biomass, agronomic efficiency, and yield of Zea mays L. on a tropical acidic soil. Triple superphosphate (TSP), Egypt Rock phosphate (ERP), and Christmas Island Rock phosphate (CIRP) were used as P sources. The treatments evaluated were: (i) soil alone, (ii) 100% recommended fertilizer rate (NPK), and (iii) 75% fertilizer rate + Clinoptilolite zeolite. Selected soil chemical properties and P availability were determined before and after field trials. Zea mays L. above-ground biomass, nutrient concentration, nutrient uptake, agronomic efficiency, and fresh cob yield were also determined. Results revealed that the effects of treatments with and without CZ treatments on soil pH, P fractions, soil acidity, dry matter production, yield of maize, nutrient uptake, and agronomic efficiency were similar. Hence, suggesting CZ inclusion in the fertilization program of Zea mays L is beneficial in terms of reducing excessive or unbalanced use of chemical fertilizers due to reduction of fertilizers usage by 25%.

Influence of Different Rates of Nitrogen (N) and Phosphorus (P) Fertilizers on Growth and nutrient use efficiency of Hevea brasiliensis

The effect of N and P on nutrient concentrations, growth and vegetative traits of rubber (RRIM 2025) clone was evaluated. The treatments consisted 9 combinations of nitrogen (Urea) and phosphorus (Christmas Island Rock Phosphate – CIRP) with fixed rate of potassium (1.5 g per plant). The treatments were applied at different rates T1 (39.49 g), T2 (42.10 g), T3 (38.18 g), T4 (27.28 g) and T5 (26.10 g). The seedlings were planted in 15 cm x 30 cm filled with an Oxisol soil. Soil containing treatment (T2) significantly increased the seedlings growth like height and girth size than the remaining treatments. The results found that seedlings grown with T2 recorded higher chlorophyll content than the seedlings that were grown with T1, T4 and T5. Noticeably seedlings that was grown with T1 (39.49 g), T2 (42.10 g), and T3 (38.18 g) significantly had a higher shoot dry weight (SDW) than seedlings that were grown with T4 (27.28 g) and T5 (26.10 g). The same scenario was noticed in total dry weight (TDW) of the seedlings where T1 (68.64 g), T2 (73.30 g) and T3 (67.08) significantly recorded higher total dry weight than seedlings that were grown with T4 (50.29 g) and T5 (48.86 g). The result shows reflected a correlation between the SDW and TDW with respect to similar influence of the treatments on both the vegetative traits. Higher nitrogen content was recorded in seedlings rubber that were grown with T2 (3.57%) and significantly different from the seedlings that were grown with other treatments. The results of this study showed that higher dosage of fertilizer may not be necessary for the rubber seedlings. Application of fertilizers at the rate T2 which contains 2.0 g urea/plant and 7.5 g CIRP/plant could be considered as the optimum amount of fertilizer required for the rubber seedlings.

Influence of Different Rates of Nitrogen (N) and Phosphorus (P) Fertilizers on Growth and nutrient use efficiency of Hevea brasiliensis

The effect of N and P on nutrient concentrations, growth and vegetative traits of rubber (RRIM 2025) clone was evaluated. The treatments consisted 9 combinations of nitrogen (Urea) and phosphorus (Christmas Island Rock Phosphate – CIRP) with fixed rate of potassium (1.5 g per plant). The treatments were applied at different rates T1 (39.49 g), T2 (42.10 g), T3 (38.18 g), T4 (27.28 g) and T5 (26.10 g). The seedlings were planted in 15 cm x 30 cm filled with an Oxisol soil. Soil containing treatment (T2) significantly increased the seedlings growth like height and girth size than the remaining treatments. The results found that seedlings grown with T2 recorded higher chlorophyll content than the seedlings that were grown with T1, T4 and T5. Noticeably seedlings that was grown with T1 (39.49 g), T2 (42.10 g), and T3 (38.18 g) significantly had a higher shoot dry weight (SDW) than seedlings that were grown with T4 (27.28 g) and T5 (26.10 g). The same scenario was noticed in total dry weight (TDW) of the seedlings where T1 (68.64 g), T2 (73.30 g) and T3 (67.08) significantly recorded higher total dry weight than seedlings that were grown with T4 (50.29 g) and T5 (48.86 g). The result shows reflected a correlation between the SDW and TDW with respect to similar influence of the treatments on both the vegetative traits. Higher nitrogen content was recorded in seedlings rubber that were grown with T2 (3.57%) and significantly different from the seedlings that were grown with other treatments. The results of this study showed that higher dosage of fertilizer may not be necessary for the rubber seedlings. Application of fertilizers at the rate T2 which contains 2.0 g urea/plant and 7.5 g CIRP/plant could be considered as the optimum amount of fertilizer required for the rubber seedlings.

Effects of incubation period and Christmas Island rock phosphate with different rate of rice straw compost on phosphorus availability in acid soil

Phosphorus (P) availability is limited in tropical acid soil due to fixation of soluble inorganic P by aluminium (Al) and iron (Fe). Liming is one of the common ways to overcome this problem. However, this practice is not economical. The aim of this study was to evaluate the effects of laboratory incubation period and different rates of rice straw compost on the soil P availability. During the incubation study, Christmas Island rock phosphate (CIRP) fertilizer was amended with different rates of rice straw compost (5, 10, 15, and 20 t ha−1). Treatments were incubated in the laboratory for 30, 60, and 90 days. Application of rice straw compost with CIRP significantly increased soil available P at 30, 60, and 90 days of incubation, respectively. This implies rice straw compost plays an important role on soil P availability by decreasing the P adsorption due to the competing adsorption sites by organic anion and dissolving the mineral associated P by low-molecular-weight organic acids. Besides, rice straw compost also increased the soil pH, and, at the same time, reduced exchangeable acidity, exchangeable Al and Fe. As the soil pH increased, the compost effectively fixed the Al and Fe in the soil instead of P, thus increasing the P availability in the soil. However, there was no significant increase/loss of available P when the incubation time increases under treatments with rice straw compost. This implies the effectiveness of rice straw compost in minimizing the loss of P due to P fixation in soil and slow microbially mediated mineralization of soil organic P to inorganic P as incubation time increases. The findings suggest that the application of rice straw compost altered soil chemical properties in a way that enhanced the availability of P in the Rengam acidic soil.

The Ability of Streptomyces spp. Isolated from Iranian Soil to Solubilize Rock Phosphate

Many agricultural soils are deficient in plant available phosphate and hence not able to sustain optimal crop productivity. The problem is due to the ability of many soils to fix phosphate in a wide range of soil pH and ecological conditions. There is a need to search for more environmental friendly alternatives to improve soil fertility and crop production in phosphate deficient soil. The aim of this study was to isolate, screen, and characterize phosphate solubilizing actinomycetes found in different types of soil with varied pH from various sites in Iran. Phosphate solubilizing ability of the actinomycetes was evaluated both on modified Pikovskaya's (PVK) agar and into broth media containing Christmas Island Rock Phosphate (CIRP). The abilities of each isolate to solubilize phosphorus was evaluated from day 1 to day 14 after inoculation. Streptomyces spp. were identified morphologically under scanning electron microscope (SEM). About 31% (22/70) isolates of actinomycetes were found to have the ability to solubilize (CIRP). Isolates IA15 and IA31 showed high solubilizing index (SI) on agar medium whereas isolates IA61, IA59, IA38, IA35, and IA31 were determined to have high CIRP solubilizing ability in broth medium. Isolates IA11, IA31, IA10, and IA61 had high pH decrease in broth medium after 14 days of inoculation. A gradual decrease in pH was observed over a 14 day period of incubation, suggesting a slow release of phosphate from CIRP. The mechanism of solubilization was related to pH decrease in broth medium. In general, majority of phosphate solubilizing actinomycetes revealed superior ability to solubilize CIRP. Key words: rock phosphate; solubilizing phosphate; Streptomyces spp

Use of Clinoptilolite Zeolite to Reduce Christmas Island Rock Phosphate use in Zea mays Cultivation on an Acid Soil

This study was conducted to (i) Determine dry matter production, nutrients concentration, nutrients uptake and use efficiency of Zea mays by including clinoptilolite zeolite in the fertilization program of Zea mays planted on an acid soil and (ii) Determine the effect of including Clinoptilolite zeolite in the fertilization program of Zea mays on selected chemical properties of an acid soil. The effect of Clinoptilolite zeolite application with 75% of fertilizers (C2) and 100% fertilizers (C1) on soil chemical properties were statistically similar. Similar observation was made for dry matter production, nutrients concentration, nutrients uptake and nutrients use efficiency. These suggest that substituting 25% of N, P and K fertilizers with Clinoptilolite zeolite is more beneficial compared to 100% application of these fertilizers. Clinoptilolite zeolite strong affinity for monovalent cations ensured timely availability of P by exerting more soil exchange sites to occupy Al3+ and Fe2+.

Use of zeolite in maize (Zea mays) cultivation on nitrogen, potassium and phosphorus uptake and use efficiency.

Concerns about unbalanced use of fertilizers leading to environmental pollution have been globally expressed. As a result, studies on how to use efficient methods to reduce nutrient applications at the same time increasing or maintaining crop yield, reducing nutrient losses and improving nutrient use efficiency are imperative. Nutrient loss due to leaching, volatilization and fixation upon fertilizer application to soils may be reduced through the use of slow-release fertilizers. A pot study was conducted to investigate if the use of inorganic fertilizers together with zeolite will improve nitrogen (N), phosphorus (P) and potassium (K) uptake and efficiency in maize (Zea mays) cultivation on Nyalau series (Typic Paleudalts). Maize hybrid no. 5 variety was used as test crop. Treatments evaluated were: (i) Unfertilized condition (T1), (ii) normal N, P and K application (7.4 g urea + 11.3 g Christmas Island rock phosphate (CIRP) + 3.8 g muriate of potash (MOP)) (T2), (iii) 135 g zeolite + 5.92 g urea+9.0 g CIRP + 3.0 g MOP (T3), (iv) 270 g zeolite + 4.44 g urea + 6.8 g CIRP + 2.3 g MOP (T4), (v) 405 g zeolite+3.0 g urea+4.5 g CIRP+1.5 g MOP (T5) and (vi) 540 g zeolite + 1.5 g urea + 2.3 g CIRP + 0.8 g MOP (T6). The effect of T2, T3, T4, T5 and T6 on soil N, P and Mg at harvest was not significantly different compared with T1. However, treatments with zeolite significantly increased K and Ca contents of soil compared to T1. Irrespective of treatment, dry matter production was not different. However, nutrient concentrations determined in plant tissues were clearly affected by the addition of zeolite. N, P and K uptake varied significantly but T6 significantly affected N, P and K use efficiency. The use of inorganic fertilizers mixed with zeolite remarkably increased N, P and K uptake, and their use efficiency in leaves, stem and roots. The use of zeolite could be beneficial with respect to nutrient retention in soil and their use efficiency.

Solubility of Rock Phosphate and its Effect to the Growth and Yield of Maize on Ultisols

Phosphor is a macro nutrients and it becomes the main limiting factor for maize growth on Ultisols. Rock phosphate is one of P fertilizer sources contains high P and Ca content, slow release and soluble under acid condition, suitable for acid soil. The objective of this research is to study the solubility of rock phosphate and its influence to the growth and yield of maize on Ultisols. This research was conducted in the research laboratory and the green house of Indonesia Soil Research Institute (ISRI). Ultisols soil samples were taken from oil palm plantation in North Sumatera. Christmas Island Rock Phosphate (CIRP) and Tunisia rock phosphate was used in this research. There are two activity conducted simultaneously, which is application of rock phosphate on Ultisols under plant indicator and without plant. The experimental design is randomized complete block design with 5 treatments and 3 replications. The pot experiment without plant was conducted using1 kg of soil sample mixed with rock phosphate treatment and placed into plastic plot. During 3 months of incubation, soil water content was maintained under field capacity by aquadest. The dosages of P fertilizer were 0, 157.6 and 315.2 kg P2O5 ha-1. Soil samples were taken on 1, 2, and 3 months after P fertilization for measuring pH, P content (by HCl 25 %, Bray 1 and Olsen extraction), P-inorganic fractionation (Al-P, Fe-P, Rs-P and Ca-P), exchangeable acidity (Al and H), Al and free of Fe oxide. The pot experiments with maize were conducted using 7.5 kg soil samples mixed with 2 different rock phosphates as a treatment. The dosages of rock phosphate were similar with experiment 1. Urea 300 kg and 150 kg KCl ha1 were applied as a basal fertilizer. Maize was planted two seed per pot and maintain until harvest time. The result of the research shows that soil P content increase with RP application, Tunisia rock phosphate give higher response than the CIRP. Direct application of rock phosphate with Fe and Al content did not increase significantly the Aldd, Al2O3 and Fe2O3 content on soil. Application of CIRP and Tunisia rock phosphate increased maize growth and yield significantly.

Towards Growing Bario Rice on Lowland Soils: A Preliminary Nitrogen and Potassium Fertilization Trial

A pot study was carried with the following objectives: (i) To investigate N and K uptake of Bario rice on Bekenu series (Tipik Tualemkuts), and (ii) To investigate N and K use efficiency of Bario rice on Bekenu series. Treatments evaluated were: (i) Bario rice under fertilized condition (T1), and (ii) Bario rice under unfertilized condition (T0). The experiment was conducted in a glasshouse at Universiti Putra Malaysia Bintulu Campus, Sarawak, Malaysia. Altogether 18 pots were used. The experimental design was completely randomized design (CRD) with 9 replications. Nitrogen and K were applied in the forms of urea (46 % N) and muriate of potash (60 % K2O) at the rates of 0.52 g N g and 0.60 g K2O per pot respectively at specific times. The fertilizers applications were done 20 and 45 days after seeding (for T1 only). However, P was applied to T1 pots only in the form of Christmas Island Rock Phosphate (36 % P2O5) at a rate of 0.54 g P2O5 per pot. At 65 days after planting, the Bario rice plants were sampled and partitioned into roots and stem. Their dry weight, N, and K concentrations determined using standard procedures. Soil sampling was done before and after fertilization stages. Soil total N was determined using the Kjeldahl method while exchangeable K, Ca, Na, and Mg were extracted using the double acid method and their concentrations determined using atomic absorption spectrophotometry. Dry ashing method was used for the determination of K, Ca, Na, and Mg concentrations in plant tissues while the Kjeldahl method was used to determine total N in plant tissues. The concentrations multiplied by the oven dried weight of roots and stem provided N, K, Ca, Na, and Mg uptake in these plant parts. The N and K use efficiency were then calculated using the subtraction method. With the exception of Ca, urea and KCl (MOP) application significantly increased soil N, K, Mg, and Na concentrations. Total dry weight for both stem and roots showed no significant difference under T1 and T0. Except for Mg concentration in stem and roots, K concentration in stem and that of N in roots were significantly higher under T1 than under T0. The other comparisons showed no significant difference. Due to N and K fertilization, there was significant increase in plant height and number of panicles under T1 compared to T0. Nitrogen, K, Na, and Mg uptake in stem were significantly higher for T1 than T0. However, those of roots were not significantly different. The overall N and K use-efficiency of the Bario rice were 9.90 % and 4.23 % respectively, and were considered low, indicating that rice grown within the time frame of this study did not efficiently utilize these nutrients. This was partly attributed to low N and K recovery during reduced condition and low organic matter status of Bekenu series as Bario rice is noted for being cultivated organically. Additionally, slow adaptation to inorganic fertilizers and sudden climatic change involved in this study cannot be ruled out as one of the reasons for the low efficiency because the rice is traditionally cultivated in the highlands of Sarawak, Malaysia. However, with appropriate fertilization and soil maintenance (through further research), Bekenu series could be used for Bario rice production. Probably supplementing inorganic fertilizers with organic ones may help to improve growth and development of this rice on Bekenu series. Future studies may consider mimicking or modifying the environment to suit Bario rice growth and development at lower elevations. Certainly, the quality of Bario rice at lower elevations should also be considered in future fertilization programmes or trials.

THE EFFECTIVENESS OF VESICULAR‐ARBUSCULAR MYCORRHIZAS IN INCREASING GROWTH AND PHOSPHORUS UPTAKE OF SUBTERRANEAN CLOVER FROM PHOSPHORUS SOURCES OF DIFFERENT SOLUBILITIES

SUMMARYThe effect of inoculation, with a VA mycorrhizal fungus on growth and phosphorus uptake of subterranean clover was examined using three phosphorus sources with different solubilities. Mycorrhizas markedly increased growth and phosphorus content of tops at intermediate rates of phosphorus application for all sources.The effectiveness of phosphorus for plant growth for mycorrhizal plants relative to non‐mycorrhizal plants was the same for a water soluble source (superphosphate) and two insoluble sources (C‐grade Christmas Island rock phosphate and calcined Christmas Island rock phosphate). The effectiveness of phosphorus from each of the three sources for phosphorus uptake by mycorrhizal plants relative to non‐mycorrhizal plants was also independent of the solubilities of the phosphorus sources applied.At a given phosphorus concentration in tops, non‐mycorrhizal subterranean clover produced more dry matter than mycorrhizal clover supplied with superphosphate. Mycorrhizal and non‐mycorrhizal subterranean clover supplied with C grade rock phosphate had the same dry weight at a given phosphorus concentration in their tops.VA mycorrhizas increased zinc but not calcium uptake by subterranean clover.

Rhizobia in tropical legumes—XI. survival in the seed environment

Factors affecting rhizobia in the seed environment of the legumes Cajanus cajan, Centrosema pubescens, Glycine max, and Psophocarpus tetragonolobus were investigated. These included the effects of fungicides, insecticides, and herbicides on the survival and growth of rhizobia on agar and in liquid cultures. The pesticides used varied in their toxicity towards rhizobia but many fungicides and insecticides could be used in the vicinity of inoculated seeds. Certain fungicides and insecticides were shown to have little or no effect on the Rhizobium-legume symbiosis of C. cajan, C. pubescens, G. max, and P. tetragonolobus when added directly to inoculated seed. Various protective pelleting procedures were investigated including preparation of coating materials containing rock phosphates from different localities, talc, and bonemeal. These were applied to the seed in mixtures suspended in aqueous solutions of substituted celluloses, or gum arabic. Talc and Christmas Island rock phosphate both proved satisfactory, while “Cellofas” is recommended as the adhesive in this formulation. Soaking seeds before pelleting in an effort to remove anti-rhizobial substances from G. max seeds was beneficial in the case of soyabean cultivar KS437, but harmful when applied to Palmetto seeds.

II On a Kokotau silt loam

Abstract Trials on a Kokotau silt loam showed a 20% response in pasture dry matter yield to Ibex phosphate and a 4.5% response to gypsum over a 6-year period. In a comparison of forms of phosphatic fertilisers, yield, P concentration, and P uptake data placed the fertilisers in the following order of decreasing efficiency: Thermophos, superphosphate, Calcined“C”-grade Christmas Island rock phosphate (CCIP)-superphosphate (1: 3), CCIP, Gafsa rock phosphate, Nauru rock phosphate. The trial design did not permit an accurate quantitative evaluation of relative effectiveness. Yields over the 6-year period were similar whether the fertilisers were applied annually or at 3 times the annual rate every 3 years. There was evidence that CCIP and Gafsa phosphates improved relative to superphosphate with time. Annual applications of the manufactured fertilisers increased soil Al-P and Fe-P fractions but changed occluded-P or Ca-P little. In contrast Ca-P accumulated and Al-P and Fe-P declined greatly in soils receivin...

PLUMBOGUMMITE MINERALS IN A STRONGLY WEATHERED NEW ZEALAND SOIL

SummaryPhosphate minerals of the plumbogummite group were tentatively identified in a strongly weathered and leached New Zealand soil formed from granite by comparing changes in inorganic phosphate fractions, after calcination, of a soil sample with those occurring in Christmas Island rock phosphate. This identification was confirmed by X‐ray diffraction. Plumbogurnmite minerals were mainly concentrated in the so‐called residual organic P fraction with a lesser but significant proportion in the residual inorganic P fraction. Phosphate minerals of this group may be quite common in other strongly weathered New Zealand soils.

RELATIONSHIP OF INORGANIC PHOSPHATE FRACTIONS T O MINERALOGICAL CHANGES IN CALCINED CHRISTMAS ISLAND ROCK PHOSPHATE

SummaryA close relationship exists between inorganic phosphorus fractions and mineralogical changes in ‘C’‐grade Christmas Island rock phosphate calcined at temperatures up to 1100 °C. Amounts of acid‐extractable Ca‐P closely followed the presence and crystallization of calcium phosphates. Amounts of NH4F‐P were related to the presence of simple aluminium phosphates. The ammonium fluoride reagent did not extract more complex aluminium phosphates such as crandallite and millisite. These minerals were considered to be present in the 2nd NaOH‐P and residual‐P fractions. NH4F‐P plus acid‐extractable Ca‐P was closely related to radish growth responses.

Tests for phosphates from Rum Jungle, Northern Territory

Phosphate-rich rock from Rum Jungle, N.T., was tested as fertilizer against Christmas Island rock phosphate dust (CIRPD) and superphosphate in two pot and three field experiments. The Rum Jungle material had little short-term value as fertilizer, but the long-term residual effects were about 60 per cent of those of CIRPD. Calcining at 450�C gave a marked improvement in short-term response in pots, but had little effect in a long-term field experiment. Pelletting the Rum Jungle material with sulphur and Thiobacillus ('biosuper') increased its effectiveness in the field at the end of the second year to the equivalent of that of superphosphate.