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- ItemEffectiveness of Panda Hills Phosphate Rock Compacted with Triple Superphosphate as Source of Phosphorus for Rape, Wheat, Maize, and Soybean(2000) Person N.S Mnkeni; Sen H. Chien; G. CarmonaGreenhouse experiments were conducted to evaluate the agronomic effectiveness of Panda Hills phosphate rock (PPR) from southwest Tanzania, its mixture with triple superphosphate (TSP), and a compacted mixture of Panda PR and TSP (PPR+TSP) for wheat, rape, maize, and soybean on two United States soils (Hiwassee and Windthorst). The mixture of Panda PR and TSP was prepared by mixing ground TSP with Panda PR in proportions such that 50% of the total phosphorus (P) in the final mixture was from TSP. The compacted product (PPR+TSP) was prepared by compacting some of the blended mixture of Panda PR and TSP into pellets using a laboratory scale Carver press followed by crushing and screening. The P rates applied to Hiwassee soil were 0, 25, 50, and 100 mg P kg for each P source and test crop while on Windthorst soil only one rate of application (50 mg P kg) was applied to one test crop (rape). A lime treatment was also included on the Windthorst soil to enable evaluation of rape response to the different P sources under calcareous conditions. Wheat and rape were allowed to grow to maturity while maize and soybean were grown for six weeks only. The performance of the P sources as reflected by yield, P uptake and relative agronomic effectiveness (RAE) followed the order TSP>>(PPR+TSP)>(PPR)+(TSP)>>PPR for wheat, rape, maize, and soybean on Hiwassee soil. Panda PR was very ineffective in increasing grain or dry‐matter yields of the test crops on this soil. The mixture of Panda PR and TSP as well as the compacted product increased wheat, maize, and soybean yields and P uptake significantly. The increases in yields were, however, largely attributed to the TSP component of the (PPR)+(TSP) mixture or its compacted product with little or no contribution from PPR. On the alkaline Windthorst soil, the performance of the P sources as reflected by rapeseed yield and RAE followed the order TSP= (PPR+TSP)>(PPR)+(TSP)>PPR. Remarkably compacted PPR and TSP was at par with TSP while PPR alone was 50% as effective as TSP in increasing rapeseed yield. Addition of lime drastically reduced the effective‐ness of Panda PR, but it had little or no effect on the agronomic effectiveness of the (PPR)+(TSP) mixture or its compacted product.
- ItemNitrogen Dynamics and Crop Growth on an Alfisol and a Vertisol under Rainfed Lowland Rice-based Cropping System(2000) Upendra Singh; S.K. Patil; R.O. Das; J.L. Padilla; V.P. Singh; A.R. PalCrop rotation experiments were conducted over 2 years to quantify N supply-demand under rainfed lowland rice±chickpea and rice±fallow cropping systems on a loam Al®sol and a clay Vertisol in India. Signi®cant differences among N rates (0, 40, 80, and 120 kg N haÿ1 ) and soils were observed with rice for grain yield, total biomass and grain N uptake in both years. Low N response, low grain yield, low N uptake, and a short grain ®lling phase during the 1995 wet season was due to post-heading water stress. The stress was more pronounced on the Vertisol and at high N rates. This resulted in lower N content at maturity than at heading. The loss of biomass N from plant implied that apparent N recovery (AR) and physiological nitrogen use ef®ciency (PNUE) may differ signi®cantly based on whether maximum N accumulation or total N uptake at maturity was used. Plant N recovery, both by the N difference method and 15N technique, revealed much lower recovery of fertilizer N (21± 27%) with rainfed lowland rice than with irrigated dry-season rice. The residual effect of N applied to the preceding rice crop was nonsigni®cant on all yield, growth, and N uptake parameters of chickpea. The performance of chickpea was better on the Al®sol than the Vertisol, principally due to soil physical attributes. The better performance and longer growth duration during 1994±1995 dry season as opposed to the 1995±1996 season was attributed to higher rainfall (92 mm versus 39 mm) and rainfall during the critical pod-®lling to maturity phase. Mineralization and nitri®cation of N was negligible during the rice± fallow period due to the dry conditions and low organic matter content. This was corroborated by the similarities in N balance between rice±chickpea and rice±fallow system. The PNUE of rice was 33 to 57 kg grain per kg N absorbed compared with 25 to 27 kg grain per kg N absorbed of chickpea, owing mostly to higher N concentration of chickpea grain and the higher energy cost due to biological N fixation.
- ItemSimultaneous Records of Methane and Nitrous Oxide Emissions in Rice-based Cropping Systems under Rainfed Conditions(2000) E.B. Abao Jr.; K.F. Bronson; Wassmann, Reine; Upendra SinghRainfed rice (Oryza sativa L.)-based cropping systems are characterized by alternate wetting and drying cycles as monsoonal rains come and go. The potential for accumulation and denitrification of NO3 - is high in these systems as is the production and emission of CH4 during the monsoon rice season. Simultaneous measurements of CH4 and N2O emissions using automated closed chamber methods have been reported in irrigated rice fields but not in rainfed rice systems. In this field study at the International Rice Research Institute, Philippines, simultaneous and continuous measurements of CH4 and N2O were made from the 1994 wet season to the 1996 dry season. During the rice-growing seasons, CH4 fluxes were observed, with the highest emissions being in organic residue-amended plots. Nitrous oxide fluxes, on the other hand, were generally nonexistent, except after fertilization events where low N2O fluxes were observed. Slow-release N fertilizer further reduced the already low N2O emissions compared with prilled urea in the first rice season. During the dry seasons, when the field was planted to the upland crops cowpea [Vigna unguiculata (L.) Walp] and wheat (Triticum aestivum L.), positive CH4 fluxes were low and insignificant except after the imposition of a permanent flood where high CH4 fluxes appeared. Evidences of CH4 uptake were apparent in the first dry season, especially in cowpea plots, indicating that rainfed lowland rice soils can act as sink for CH4 during the upland crop cycle. Large N2O fluxes were observed shortly after rainfall events due to denitrification of accumulated NO3 – . Cumulative CH4 and N2O fluxes observed during this study in rainfed conditions were lower compared with previous studies on irrigated rice fields.
- ItemRotation and nitrogen fertilizer effects on pearl millet, cowpea and groundnut yield and soil chemical properties in a sandy soil in the semi-arid tropics, West Africa(2000) Andre Bationo; B. R. NtareA 5-year study was conducted from 1988 to 1992 at three sites in Niger to determine the effects of crop rotation of a cereal and legumes and nitrogen fertilizer on chemical properties of the soil (0–20 cm) and yield of pearl millet (Pennisetum glaucum (L.) R.BR.), cowpea (Vigna unguiculata (L.) Walp.), and groundnut (Arachis hypogea L.). Four N levels and rotation treatments including continuous fallow were investigated. Soil samples taken from the top 20 cm depth at the end of the experiment from treatments without nitrogen application which included continuous fallow, fallow–millet rotation, groundnut–millet rotation, cowpea–millet rotation, and continuous millet were analysed for soil pH, organic carbon, total nitrogen and exchangeable bases. Fertilizer N significantly increased yield of pearl millet, cowpea and groundnut. Continuous monocropping of pearl millet resulted in lower yields across N levels compared to legume–millet rotations. Legume yields were also consistently lower in monoculture than when rotated with millet. There was a decline in organic matter under continuous millet, cowpea–millet rotation and groundnut–millet rotation. The fallow–millet rotation supplied more mineral N than the legume–millet rotations. Nitrogen availability was greater in cowpea–millet rotation than continuous millet. Crop rotation was more productive than the continuous monoculture but did not differ in maintaining soil organic matter. The legume–millet rotation at 30 kg}ha N appears to be the most viable for millet production. Research should focus on understanding the effect of legume}cereal intercrops and rotations on soil productivity.
- ItemLong-Term Effects of Tillage, Phosphorus Fertilization and Crop Rotation on Pearl Millet-Cowpea Productivity in the West-African Sahel(2000) G. V. Subbarao; C. Renard; W. A. Payne; Andre BationoThe millet (Pennisetum glaucum)-based cropping systems that dominate the Sudano–Sahelian Zone of West Africa cannot, as they are currently practised, meet the growing food needs of the region. They must therefore be intensified in a sustainable manner. The present study was initiated in 1986 and continued until 1996 to evaluate the effects of phosphorus (P) fertilization, tillage and rotation with sole cowpea (Vigna unguiculata) on an operational scale with two cropping systems, namely, sole millet and millet–cowpea intercropping. A randomized complete block design with four replications was used. The effects of P fertilization, ridging with animal traction and planting on ridges (AT), and rotation with sole cowpea increased the productivity of millet substantially in 10 of the 11 years. Based on the 11-year average, P fertilization alone improved grain yield by 52%, and AT with P fertilization improved grain yield by nearly 135%. Combining AT, P fertilization and the sole cowpea rotation resulted in a 200% increase in grain yield compared with the traditional system of production. Millet productivity did not show a significant decline when intercropped with cowpea. Stability and relative stability analysis showed that the traditional system was more stable than the various agronomic packages, but had the least yield. Conversely, the agronomic package with the highest yield advantage over the traditional system was the least stable. A major portion of the annual variation in the environmental index for grain yield and total dry matter was attributed to the seasonal variation in rainfall and organic matter depletion. Organic matter levels declined linearly with years of cultivation. Significant differences were found in the rate of depletion between the various agronomic treatments tested. After 11 years, nearly 60% of the organic matter was depleted irrespective of the agronomic treatments.
- ItemCereal/legume Rotation Effects on Cereal Growth in Sudano-Sahelian West Africa: Soil Mineral Nitrogen, Mycorrhizae and Nematodes(2000-01) M. Bagayoko; A. Buerkert; G. Lung; Andre Bationo; V. RömheldYield increases of cereals following legumes in rotation have been previously reported for West Africa, but little progress has been made to explain the mechanisms involved. At four sites in Niger and Burkina Faso, field trials with pearl millet (Pennisetum glaucum (L.) R. Br.), cowpea (Vigna unguiculata (L.) Walp), sorghum (Sorghum bicolor (L.) Moench) and groundnut (Arachis hypogaea L.) were conducted from 1996 to 1998 to investigate the role of soil mineral nitrogen (Nmin), native arbuscular mycorrhizae (AM) and nematodes in cereal/legume rotations. Grain and total dry matter yields of cereals at harvest were increased by legume/cereal rotations at all sites. Soil Nmin levels in the topsoil were consistently higher in cereal plots previously sown with legumes (rotation cereals) compared with plots under continuous cereal cultivation. However, these rotation effects on Nmin were much larger with groundnut than with cowpea. Roots of rotation cereals also had higher early AM infection rates compared to continuous cereals. The dominant plant-parasitic nematodes found in all experiment fields were Helicotylenchus sp., Rotylenchus sp. and Pratylenchus sp. In sorghum/groundnut cropping systems, nematode densities were consistently lower in rotation sorghum compared to continuous sorghum. Continuous groundnut had the lowest nematode densities indicating that groundnut was a poor host for the three nematode groups. In millet/cowpea cropping systems with inherently high nematode densities, crop rotations barely affected nematode densities indicating that both crops were good hosts. These results suggest that on the nutrient poor Sudano-Sahelian soils of our study, total dry matter increases of rotation cereals compared with continuous cereals can be explained by higher Nmin and AM infection levels early in the season. The site-specific magnitude of these effects may be related to the efficiency of the legume species to suppress nematode populations and increase plant available N through N2-fixation.
- ItemPhosphorus Transformations in an Oxisol under Contrasting Land-use Systems: The Role of the Soil Microbial Biomass(2001) Astrid Oberson; Dennis K. Friesen; I.M. Rao; S. Bühler; Emmanuel FrossardIt is generally assumed that phosphorus (P) availability for plant growth on highly weathered and P-deficient tropical soils may depend more on biologically mediated organic P (Po) turnover processes than on the release of adsorbed inorganic P (Pi). However, experimental evidence showing the linkages between Po, microbial activity, P cycling and soil P availability is scarce. To test whether land-use systems with higher soil Po are characterized by greater soil biological activity and increased P mineralization, we analyzed the partitioning of P among various organic and inorganic P fractions in soils of contrasting agricultural land-use systems and related it to biological soil properties. Isotopic labeling was used to obtain information on the turnover of P held in the microbial biomass. Soil samples were taken from grass–legume pasture (GL), continuous rice (CR) and native savanna (SAV) which served as reference. In agreement with estimated P budgets (+277, +70 and 0 kg P ha−1 for CR, GL and SAV, respectively), available P estimated using Bray-2 and resin extraction declined in the order CR > GL > SAV. Increases in Bray-2 and resin Pi were greater in CR than GL relative to total soil P increase. Organic P fractions were significantly less affected by P inputs than inorganic fractions, but were a more important sink in GL than CR soils. Extractable microbial P (Pchl) was slightly higher in GL (6.6 mg P kg−1) than SAV soils (5.4 mg P kg−1), and significantly lowest in CR (2.6 mg P kg−1). Two days after labeling the soil with carrier free 33P, 25, 10 and 2% of the added 33P were found in Pchl in GL, SAV and CR soils, respectively, suggesting a high and rapid microbial P turnover that was highest in GL soils. Indicators of P mineralization were higher in GL than CR soils, suggesting a greater transformation potential to render Po available. Legume-based pastures (GL) can be considered as an important land-use option as they stimulate P cycling. However, it remains to be investigated whether crops planted in pasture–crop rotations could benefit from the enhanced Po cycling in grass–legume soils. Furthermore, there is need to develop and test a direct method to quantify Po mineralization in these systems.
- ItemPhosphorus Transformations in an Oxisol under Contrasting Land-use Systems: The Role of the Soil Microbial Biomass(2001) Astrid Oberson; Dennis K. Friesen; I.M. Rao; S. Bühler; Emmanuel FrossardIt is generally assumed that phosphorus (P) availability for plant growth on highly weathered and P-deficient tropical soils may depend more on biologically mediated organic P (Po) turnover processes than on the release of adsorbed inorganic P (Pi). However, experimental evidence showing the linkages between Po, microbial activity, P cycling and soil P availability is scarce. To test whether land-use systems with higher soil Po are characterized by greater soil biological activity and increased P mineralization, we analyzed the partitioning of P among various organic and inorganic P fractions in soils of contrasting agricultural land-use systems and related it to biological soil properties. Isotopic labeling was used to obtain information on the turnover of P held in the microbial biomass. Soil samples were taken from grass–legume pasture (GL), continuous rice (CR) and native savanna (SAV) which served as reference. In agreement with estimated P budgets (+277, +70 and 0 kg P ha−1 for CR, GL and SAV, respectively), available P estimated using Bray-2 and resin extraction declined in the order CR > GL > SAV. Increases in Bray-2 and resin Pi were greater in CR than GL relative to total soil P increase. Organic P fractions were significantly less affected by P inputs than inorganic fractions, but were a more important sink in GL than CR soils. Extractable microbial P (Pchl) was slightly higher in GL (6.6 mg P kg−1) than SAV soils (5.4 mg P kg−1), and significantly lowest in CR (2.6 mg P kg−1). Two days after labeling the soil with carrier free 33P, 25, 10 and 2% of the added 33P were found in Pchl in GL, SAV and CR soils, respectively, suggesting a high and rapid microbial P turnover that was highest in GL soils. Indicators of P mineralization were higher in GL than CR soils, suggesting a greater transformation potential to render Po available. Legume-based pastures (GL) can be considered as an important land-use option as they stimulate P cycling. However, it remains to be investigated whether crops planted in pasture–crop rotations could benefit from the enhanced Po cycling in grass–legume soils. Furthermore, there is need to develop and test a direct method to quantify Po mineralization in these systems.
- ItemInterlaboratory Comparison of Soil Phosphorus Extracted by Various Soil Test Methods(2001) Peter J. A. Kleinman; A. N. Sharpley; K. Gartley; W. M. Jarrell; S. Kuo; R. G. Menon; R. Myers; K. R. Reddy; E. O. SkogleyThe widespread use of soil phosphorus (P) data, either in the context of agronomic or environmental management, requires an explicit understanding of potential errors related to soil P testing. This study compares a variety of soil P extraction methods, each performed by 9 separate laboratories on 24 soils from across the United States. Soil clay content ranged from 0 to 47%, pH from 4.2 to 8.6, and Mehlich-3 P concentration from 2 to 205 mg kg21 . Average interlaboratory coefficients of variation (CVs) ranged from 0.11 to 0.22 for solution extracts (Bray-1 P, Fe-strip P, Mehlich-3 P, and Olsen P) and from 0.11 to 0.70 for saturated paste extracts (resin capsules and resin membranes, incubated for 2, 4, and 7 days). For soil tests based upon solution extracts, Olsen P exhibited the greatest variability among laboratories ðCV ¼ 0:22Þ; despite its reputed suitability for a wider range of soils than Bray-1 and Mehlich-3. Soil test data were highly correlated, with the lowest correlations occurring between Olsen and Bray-1 P or Olsen and Mehlich-3 P (r ¼ 0:77 and 0.84, respectively) and the highest correlations occurring between Olsen P and Fe-strip P or Mehlich-3 and Bray-1 P (r ¼ 0:94 for both correlations). Results indicate that some common soil test P protocols, when carefully conducted, yield data that may be reliably compared, such as in the compilation of regional and national soil databases.
- ItemIdentification of Compounds Present in Single Superphosphates Produced From Brazilian Phosphate Rocks Using Sem, Edx, and X-Ray Techniques(2001) L. I. Prochnow; C. A. Clemente; E.F. Dillard; Adolpho Melfi; Van Kauwenbergh, S.J.Scanning electron microscope (SEM), energy dispersive X-ray (EDX) and X-ray techniques were used to obtain data about the mineralogical composition of single superphosphates (SSP) produced from apatite concentrates originating from Araxá, Jacupiranga, Catalão, and Tapira igneous phosphate rock deposits. The SSP samples were investigated both in their original form and after leaching with water to remove water-soluble compounds. Results of chemical analysis and instrumental techniques showed that P compounds were still present in the water-leached material. Anhydrite (CaSO4 with no hydration water) was the main Ca-S component in the SSP samples. Monocalcium phosphate monohydrate [Ca(H2PO4)2.H2O] was identified in the original but not in the water-leached samples. Results of SEM, EDX, and X-ray confirmed the presence of crystals of triiron (III) potassium octahydrogen hexaphosphate hexahydrate [Fe3KH8(PO4)6.6H2O] in the SSP. The results of SEM and EDX analyses suggested that the compounds triiron (III) nonahydrogen hexaphosphate hexahydrate [Fe3H9(PO4)6.6H2O], triiron (III) 15-hydrogen octaphosphate tetrahydrate [Fe3H15(PO4)8.4H2O], triiron (III) potassium 14-hydrogen octaphosphate tetrahydrate [Fe3KH14(PO4)8.4H2O], and barium sulfate (BaSO4) were present in some of the SSP samples. Use of SEM, EDX, and X-ray techniques was shown to be adequate for precise characterization of compounds present in the SSP studied, which will help to understand further the plant availability of the phosphorus contained (especially) in the water-insoluble P fraction of this fertilizer.
- ItemEfficient Phosphorus Application Strategies for Increased Crop Production in Sub- Saharan West Africa(2001) A. Buerkert ; Andre Bationo; Hans-Peter PiephoGreenhouse experiments were conducted to evaluate the agronomic effectiveness of Panda Hills phosphate rock (PPR) from southwest Tanzania, its mixture with triple superphosphate (TSP), and a compacted mixture of Panda PR and TSP (PPR+TSP) for wheat, rape, maize, and soybean on two United States soils (Hiwassee and Windthorst). The mixture of Panda PR and TSP was prepared by mixing ground TSP with Panda PR in proportions such that 50% of the total phosphorus (P) in the final mixture was from TSP. The compacted product (PPR+TSP) was prepared by compacting some of the blended mixture of Panda PR and TSP into pellets using a laboratory scale Carver press followed by crushing and screening. The P rates applied to Hiwassee soil were 0, 25, 50, and 100 mg P kg for each P source and test crop while on Windthorst soil only one rate of application (50 mg P kg) was applied to one test crop (rape). A lime treatment was also included on the Windthorst soil to enable evaluation of rape response to the different P sources under calcareous conditions. Wheat and rape were allowed to grow to maturity while maize and soybean were grown for six weeks only. The performance of the P sources as reflected by yield, P uptake and relative agronomic effectiveness (RAE) followed the order TSP>>(PPR+TSP)>(PPR)+(TSP)>>PPR for wheat, rape, maize, and soybean on Hiwassee soil. Panda PR was very ineffective in increasing grain or dry‐matter yields of the test crops on this soil. The mixture of Panda PR and TSP as well as the compacted product increased wheat, maize, and soybean yields and P uptake significantly. The increases in yields were, however, largely attributed to the TSP component of the (PPR)+(TSP) mixture or its compacted product with little or no contribution from PPR. On the alkaline Windthorst soil, the performance of the P sources as reflected by rapeseed yield and RAE followed the order TSP= (PPR+TSP)>(PPR)+(TSP)>PPR. Remarkably compacted PPR and TSP was at par with TSP while PPR alone was 50% as effective as TSP in increasing rapeseed yield. Addition of lime drastically reduced the effective‐ness of Panda PR, but it had little or no effect on the agronomic effectiveness of the (PPR)+(TSP) mixture or its compacted product.
- ItemCultivar, Nitrogen, and Water Effects on Productivity, and Nitrogen-Use Efficiency and Balance for Rice- Wheat Sequences of Bangladesh(2001-06-12) Jagadish Timsina; Upendra Singh; M. Baddaruddin; Craig A Meisner; M.R. AminRice (Oryza sativa L.) and wheat (Triticum aestivum L.) are often grown in sequences under a range of nitrogen (N), water (W), and planting date in South Asia. Field experiments were conducted from 1994-1995 to 1996-1997 to define the effects of two W and three N regimes on growth and productivity, N uptake and Nouse efficiencies, and N halance for rice-wheat systems of northern Bangladesh. Mean grain yields of rice and wheat were greatest (4.9 and 3.1 t ha", respectively) during the first and smallest (2.2 and 241 ha respectively) during the third year. The cuhivars of rice and wheat responded to imigation and to N, with greater response to irrigation in rice, but to N in wheat. Delayed wheat seeding redaced wheat yields in all years. Agronomic N-use efficiency (kg grain yield per kg N applied), physiological efficiency (kg grain yield per kg N ahsurbed), and fertilizer N-recovery efficiency (kg N absorbed per kg N applied, expressed as ) for rice across treatments ranged from 2.8 to 10.8, 5.2 to 27.5, and 33 to 61, respectively, and all were greater for N application at 90 compared with 135 kg Nha For wheat, those values ranged from 15 to 27, 33 to 51, and 45 to 63, respectively, and were greater at 120 compared with 180 kg Nha, and under irrigation than rainfed. All those parameters had greater values under irrigation than rainfed. Total soil N increased slightly after 3 years of cropping, while organic carbon and plt decreased slightly in all treatments. There was a net increase of soil ammonium N (80 kg ha) and a zero balance of N after the fest year of cropping under imgation with high N (135 and 180 kg ha for rice and wheat, respectively), but without N there was a decrease of soil mineral N (70 kg ha) with a balance of +16 kg ha. Biological N fixation accounted for N halance in N-omitted as well as N-applied treatments. The results emphasize the need for regular monitoring of weather, crop performance, imgation water, and soil and plant mineral N for further understanding the growth, productivity, N-use efficiencies, and balance in rice-wheat system.
- ItemSequential Phosphorus Extraction of a 33P-Labeled Oxisol under Contrasting Agricultural Systems(2002) S. Buehler; Astrid Oberson; I.M. Rao; Dennis K. Friesen; Emmanuel FrossardChemical sequential extraction is widely used to divide soil phosphorus (P) into different inorganic (Pi) and organic (Po) fractions, but the assignment of these fractions to pools of differing plant availability, especially for low P tropical soils, is still matter of discussion. To improve this assignment, the effect of land-use systems and related P fertilizer inputs on size of P fractions and their isotopic exchangeability was investigated. A Colombian Oxisol, sampled from a long-term field experiment with contrasting management treatments, was labeled with carrier free 33P and extracted after incubation times of 4 h, 1, and 2 wk. Phosphorus concentrations and 33P recovery in fractions sequentially extracted with anion exchange resin (Pi), 0.5 M NaHCO3 (Bic-Pi, Bic-Po), 0.1 M NaOH (Pi, Po), hot concentrated HCl (Pi, Po), and residual P were measured for each incubation time. Resin-Pi, Bic-Pi, NaOH-Pi, and hot HCl-Pi were increased with P fertilization, with the highest increase for NaOH-Pi The recovery of 33P in the treatments with annual P fertilization clearly exceeding P outputs indicate that resin-Pi, Bic-Pi, and NaOH-Pi represented most of the exchangeable P. In these treatments, label P transformed with increasing incubation time from the resin to the Bic-Pi and NaOH-Pi fractions. The organic or recalcitrant inorganic fractions contained almost no exchangeable P. In contrast, in soils with low or no P fertilization, more than 14% of the 33P was recovered in NaOH-Po and HCl-Po fractions 2 wk after labeling, showing that organic P dynamics are important when soil Pi reserves are limited.
- ItemThe Drought Response of Lowland Rice to Crop Establishment Practices and N-Fertilizer Sources(2002) To Phuc Tuong; Ernesto Guttierez Castillo; R.C. Cabangong; A. Boling; Upendra SinghIncreasing drought nevostance sont nutrient availability to the plant in inportant for increasing ysells on raised low land rice. This study investigated the effects of crop establishment and commelled release telerson drought stress responses and strogen uptake of thee (Oryon sa Le P'SBR 14 grown on a clayey kisan Vestie Tropeapple-glot field experiment. The main plots were two wateteywelltered and vaghoressed for 20 days from pасе The subplos comprised of three crop establishment method is the sub-speilleuren was compared with Polyon 12 and POC-5120 Desighi pesolonged crop maturity by about 20 days and greatly reduced grais yield but not the total biomass and tal Nuptake Dry-seeded ice had a lower yield in the well-wared treatment higher yield in the stress compared with transplaned and wet seeded ice. The higher yield of dry seeded rice under sates could be related its significantly higher rock length density, higher ros-shoots and more uniform nov domibunun with respect te sed depth and higher available soil motore in the root zone during the stres period Under the well-watered condition, yields in all fertilites were comparable. In the stress tremen Polo 12 prosaces the lowest yield probably because of the monutch between used pilongation of crop duration and the release period of 12.
- ItemEvaluation of Available Phosphorus and Cadmium Associated with Phosphate Rock for Direct Application(2002) Sen H. ChienThree greenhouse experiments were conducted to evaluate available P and Cd associated with the use of phosphate rock (PR) for direct application. These experiments were: (1) "Estimation of Phosphorus Availability to Maize and Cowpea From Phosphate Rock as Enhanced by Water-Soluble Phosphorus;" (2) "Modified Iron Oxide-Impregnated Paper Strip (Pi) Test for Soils Treated With Phosphate Fertilizers;" and (3) "Effect of Acidulation of High Cadmium Containing Phosphate Rocks on Cadmium Uptake by Upland Rice." In the first experiment, a medium-reactive Central Florida phosphate rock (PR) was used. The effectiveness of P sources in terms of increasing dry-matter yield and P uptake followed the order of TSP > (PR + TSP) > PR for maize and TSP = (TSP + PR) > PR for cowpea. P uptake from PR in the presence of TSP was higher than P uptake from PR applied alone. With respect to P uptake from PR applied alone, the corresponding relative increase in P uptake from PR due to TSP influence was 165% for maize and 72% for cowpea. In the second experiment, a highly reactive North Carolina PR was used. Both Bray I and the Pi test (with CaCl2) underestimated available P from PR with respect to TSP. Available P estimated by the Pi test with KC1 was more closely related to P uptake with both PR and TSP. More P was extracted from PR by the Pi test with KC1 than with CaCl2, whereas no effect was observed for TSP. In the third experiment, a low-reactive Togo PR and a highly reactive North Carolina PR were used. Both PRs were fully acidulated to SSP and Togo PR was also partially acidulated with H2SO4 at 50% level to PAPR. Cd uptake by rice grain followed the order of NC-SSP > NC-PR and Togo-SSP > Togo PAPR > Togo PR. The results also showed that most of the Cd uptake was retained in rice root and straw. Total uptake of Cd, Ca, and P by the rice plant was higher from NC-PR than from Togo-PR. Cd concentration in rice grain showed no significant difference between NC-PR and Togo-PR, whereas Cd concentrations in root and straw were higher with NC-PR than that with Togo-PR
- ItemEvaluation of DSSAT Soil-Water Balance Module Under Cropped and Bare Soil Conditions(2003) Rogério Teixeira de Faria; Walter Truman BowenThe performance of the soil water balance module (SWBM) in the models of DSSAT v3.5 was evaluated against soil moisture data measured in bare soil and dry bean plots, in Paraná, southern Brazil. Under bare soil, the SWBM showed a low performance to simulate soil moisture profiles due to inadequacies of the method used to calculate unsaturated soil water flux. Improved estimates were achieved by modifying the SWBM with the use of Darcy’s equation to simulate soil water flux as a function of soil water potential gradient between consecutive soil layers. When used to simulate water balance for the bean crop, the modified SWBM improved soil moisture estimation but underpredicted crop yield. Root water uptake data indicated that assumptions on the original method limited plant water extraction for the soil in the study area. This was corrected by replacing empirical coefficients with measured values of soil hydraulic conductivity at different depths.
- ItemThe Prospects for Integrated Nutrient Management for Sustainable Rainfed Lowland Rice Production in Sukumaland, Tanzania(2003) H.C.C. MeertensThe possibilities of integrated nutrient management for sustainable rice cultivation are investigated for rainfed, lowland rice in Sukumaland, northwestern Tanzania. Typical, hardpan rice soils in Sukumaland have rather low levels of organic matter, total nitrogen and available phosphorus, and a low to medium amount of exchangeable potassium. Consumption of mineral fertilizers in rice is, however, very low due to availability problems and sharply increased prices of fertilizers. Use of locally available resources for soil fertility improvement is hampered by the additional inputs of farm household labour involved. High labour inputs per hectare without increases in capital inputs lead to lower marginal and average products per hour of labour. Furthermore, in semi-arid Sukumaland biomass production of green manures is seriously restricted by climate. The amount of kraal cattle manure is insufficient and half the households have no easy access to it. Using rice straw as cattle feed and thatching material has priority over soil fertility improvement. Some farmers indicate that at present there is not yet an urgent need for improved integrated nutrient management in Sukumaland rice cultivation. Adoption of integrated nutrient management based technologies depends on conducive socio-economic, agro-ecological and public policy circumstances. Farmer investment in learning and a favourable policy environment are thus no guarantee for worldwide adoption of these technologies by farm households.
- ItemDevelopment of a Soil-plant Phosphorus Simulation Model for Calcareous and Weathered Tropical Soils(2003) Samira H. Daroub; Argyrios Gerakis; Joe T. Ritchie; Dennis K. Friesen; John RyanPhosphorus (P) is a limiting nutrient affecting crop yields in many regions of the world, in particular in areas with highly weathered acid soils and calcareous alkaline soils. Given the many factors associated with P behavior in a range of soil environments, there is a need to go beyond site-specific situations. The use of crop simulation models is a valuable tool to evaluate the efficacy of applying P fertilizers under different soil, management and climatic conditions. A computer model was developed to simulate P in the soil–plant system adapted to soils with high P limitations. The soil P module is operated with two comprehensive crop simulation models (CERES and CROPGRO) within the DSSAT software. The P module comprises inorganic and organic P pools estimated from measured P fractionation data and works on a daily time step. The rate constants for P movement between the pools follow first order kinetics. The P module was calibrated and tested using three data sets from Colombia, Syria, and Tanzania. The limited testing showed that the P module simulated accurately grain yield and P uptake by wheat grown under semi-arid conditions. The wheat crop responded little to fertilization although measured Olsen P was as low as 2.6 mg kg-1 . The P module overestimated P uptake for both soybean and bean crops grown in acidic soils, but predicted with a good degree of accuracy labile P in the soil and P uptake for maize grown under the same acidic conditions. Testing with more data sets is needed to improve model predictions.
- ItemEvaluation of Rape Response to Different Sources of Phosphate Rock in an Alkaline Soil(2003) Sen H. Chien; G. Carmona; Julio Henao; L. I. ProchnowA greenhouse experiment was conducted to evaluate the agronomic effectiveness of one unground, as received from Tunisia, and eight finely ground phosphate rock (PR) sources from Syria, Kazakhstan, Jordan, Russia, Mali, Burkina Faso, Tanzania, and China as compared with TSP for rape grown on an alkaline soil (pH 7.7). The P rates applied were 0, 5, 10, 25, and 50 mg P kg−1. The rape was grown to maturity. The yield of rapeseed obtained with each P source was fitted to a linear function with P rate. The relative agronomic effectiveness (RAE) of each PR with respect to TSP was calculated as the ratio of the slopes of the response function. The results show that RAE ranged from 0 to 88%, depending on the reactivity of PR. RAE correlated highly with the solubility of all PR sources as measured by 2% citric acid (CA) (R2=0.947) in a semi-log function. When the unground, highly reactive PR was excluded in the correlation, R2 was increased to 0.957 with 2% CA. The correlation was also very high (R2=0.963) when the RAE of the unground PR was plotted against its solubility measured in the finely ground form along with other finely ground PR sources. Low-reactivity PR with 2% CA-soluble P as low as 2.5% P can be 50% as effective as TSP in increasing yield of rapeseed even in alkaline soils. Use of indigenous PR sources, especially high reactive, for rapeseed production is feasible in those countries where agricultural soils are alkaline.
- ItemSynthesis, Characterization, and Agronomic Evaluation of Iron Phosphate Impurities in Superphosphates(2003) L. I. Prochnow; Sen H. Chien; E.F. Dillard; Austin, E. Rick ; G. Carmona; Julio Henao; Upendra Singh; R. W. TaylorTwo of the most common impurities found in superphosphates processing marginal-grade PR was reported by Bartos (single superphosphate [SSP] and triple superphosphate [TSP]) in et al. (1992), Mullins et al. (1995), Mullins and Sikora the forms of Fe3KH8(PO4)6·6H2O and Fe3KH14(PO4)8·4H2O were syn- (1995), and Prochnow et al. (1998). The results showed thesized (H8-syn and H14-syn, respectively), characterized, and agro- that water solubility of these acidulated P fertilizers nomically evaluated to investigate cost-effective means to optimize required for maximum crop yield was lower than that the utilization of phosphate rocks (PRs) containing Fe impurities. A accepted by some legislation (Official Journal of the solubility study showed that more P was released from both com- European Communities, 1975; Brasil, 1982). However, pounds as pH increased in the 0.01 M KCl solutions (pH 3.0–7.5) and little attempt has been made to adequately characterize more P was released from H14-syn than H8-syn. The two Fe-K-P the impurity compounds present in acidulated P fertiliz- compounds were mixed and compacted with monocalcium phosphate ers, especially in SSP and TSP or to produce large quan- (MCP) at 0, 25, 50, 75, and 100% of total P as MCP. In a greenhouse tities under laboratory conditions for agronomic eval- study, rates of P were applied at 0, 10, 20, 40 and 80 mg P kg 1 from H8-syn, H14-syn, and MCP, while the compacted mixtures were uation. applied only at 40 mg P kg 1 to an Ultisol (thermic Rhodic Kanhaplu- In SSP and TSP, two of the most common waterdults, pH 5.3) cropped with upland and flooded rice (Oryza sativa insoluble P impurities are the generic compounds H8 L.) for 65 d. The results showed that P uptake and dry-matter yield and H14 (Lehr et al., 1967; Frazier et al., 1991). These were greater with H14-syn than H8-syn for both crops and both compounds preferentially form the K-containing com- compounds were more effective for flooded rice than upland rice. pounds, but in the absence of K in solution, Na-con- The calculated values of relative agronomic effectiveness (RAE) of taining compounds will form [(Fe,Al)3NaH8(PO4)6·6H2O H8-syn and H14-syn with respect to MCP were 32 and 72% in dry- or (Fe, Al)3NaH14(PO4)8·4H2O] or even as the analog H9 matter yield for upland rice and 55 and 102% for flooded rice, respec- or H15 members [(Fe, Al)3H9(PO4)6·6H2O or (Fe,Al)3 tively. To reach 90% of maximum dry-matter yield obtained with H15(PO4)8 MCP, it required approximately 43 and 35% of total P as water- ·4H2O] (Frazier et al., 1991; Sullivan et al., soluble P (WSP) in the mixtures of H8-syn and H14-syn with MCP 1991). According to Lehr et al. (1967) and Frazier et for upland rice and only 17 and 11% for flooded rice, respectively.