Optimum Phosphorus Concentration for Growth of Catharanthus roseus (L.) G. Don ‘Pacifica White’ in a Subirrigation and Top Watering System

The objective of this study was to quantify the optimum rates of water-soluble phosphorus (P) on the growth of Catharanthus roseus (L.) G. Don ‘Pacifica White’ in soilless media in a recirculating subirrigation and top watering system. The experiment was designed so that only P varied between treatments; nitrogen (N), ammoniacal N to nitrate N ratio, and potassium (K) content were held constant. Media pH decreased with increasing P concentration in the nutrient solution in both the subirrigated and top-watered plants. Shoot N, P, K, magnesium, manganese, zinc, and copper were in general greater in the subirrigated plants when compared to top-watered plants. Shoot calcium, sulfur, iron, aluminum, and boron were greater in top-watered plants when compared to subirrigated plants. Optimal plant growth was achieved at ≥0.5 mM P in the subirrigated and top-watered plants, which is lower than what is usually commercially applied. Subirrigated plants were of greater quality and dry mass regardless of P concentration in the nutrient solution, when compared to top-watered plants.     

Phosphorus–Zinc Interactions in Two Barley Cultivars Differing in Phosphorus and Zinc Efficiencies

Abstract

Phosphorus (P)–zinc (Zn) interactions in two barley cultivars (Clipper and Sahara) differing in P and Zn efficiencies were investigated in a pot experiment carried out in a growth chamber. A highly calcareous field soil from a semi‐arid region of South Australia was used. Five levels of P addition and three levels of Zn addition were used. Plants were harvested five weeks after emergence. Increase in P supply significantly increased plant shoot biomass and tissue P concentrations in both cultivars, indicating that the soil used is P deficient. Zinc additions with low P additions caused slight decreases in plant biomass. However, Zn addition did increase plant growth when higher levels of P were applied demonstrating the importance of the balance Zn and P supply. Results showed that the genotypic difference between the two cultivars in P uptake efficiency (specific P uptake, SPU) can be altered by Zn–P interactions, and that total Zn uptake by Sahara was higher than Clipper irrespective of P supply. Tissue Zn concentrations decreased significantly with an increase in P supply in both cultivars. Increase in P supply drastically reduced the molar ratio of Zn to P in shoots (MRZP), and addition of Zn compensated for the reduction in MRZP due to P addition. The role of P–Zn interactions in the context of nutritional quality of plant food is also discussed.     

Fast analysis of sugars, fruit acids, and vitamin C in sea buckthorn (Hippophaë rhamnoides L.) varieties

A fast, one-step gas chromatographic method was developed to analyze trimethylsilyl (TMS) derivatives of sugars, fruit acids, and ascorbic acid in sea buckthorn (Hippoha? rhamnoides L.) berries. The method was applied to berry press juice of sea buckthorn of different origins grown in Finland during the 2003 and 2004 seasons. The method gave reliable results for D-fructose, D-glucose, ethyl-D-glucose, and malic, quinic, and ascorbic acids, which are the major sugars and acids in sea buckthorn juice. For the first time in sea buckthorn and evidently in any berry, the presence of ethyl beta-D-glucopyranoside is reported. The structure of ethyl glucose was verified by high-performance liquid chromatography (HPLC), gas chromatography (GC), MS, and NMR analyses of both the isolated and the synthesized compounds. In the GC method, vitamin C was analyzed as ascorbic acid only, and dehydroascorbic acid was thus not taken into account.     

AM fungi lead to fertilizer phosphorus economy and enhanced system productivity and profitability in okra (Abelmoschus esculentus L.)–pea (Pisum sativum L.) cropping system in Himalayan acid Alfisol

The present investigation was carried out at CSK Himachal Pradesh Agricultural University, Palampur, Himachal Pradesh, India, during 2009–2011 to economize inorganic phosphorus (P) and enhance profitability of okra (Abelmoschus esculentus)–pea (Pisum sativum) cropping system through arbuscular mycorrhizal fungi (AMF). A field experiment was replicated thrice in a randomized block design comprising 14 treatments involving AMF (Glomus mosseae) at varying inorganic P (50%, 75%, and 100% of recommended soil test-based P dose) and irrigation regimes (40% and 80% available water capacity] in a Himalayan acid Alfisol. In okra, AMF inoculation at varying P and irrigation regimes registered higher P response ratio (PRR), net returns (10–18%), and benefit:cost (B:C) ratio (17–49%) compared to “generalized recommended P dose (GRD)” and their non-AMF counterparts. Similarly in pea, AMF inoculation at varying P and irrigation regimes again registered higher PRR, net returns (14–23%), and B:C ratio (10–58%) compared to GRD and non-AMF counterparts. Higher system productivity (7–16%) and profitability in terms of net returns (9–23%) and B:C ratio (10–54%) were also registered in AMF-imbedded treatments compared to non-AMF counterparts. Further, “AMF + 75% soil test-based P dose” at either of these irrigation regimes registered statistically similar okra–pea system productivity and profitability as that obtained under “100% soil test-based P dose” at either of two irrigation regimes, thus indicating an economy of soil test-based applied P dose by about 25%. Overall, the current study suggests that practice of AMF inoculation has great potential in enhancing system productivity and profitability besides cutting down about 25% inorganic P requirement in okra–pea production system in the Himalayan acid Alfisol.     

Influence of AM fungi,inorganic phosphorus and irrigation regimes on plant water relations and soil physical properties in okra (Abelmoschus esculentus L.) – pea (Pisum sativum L.) cropping system in Himalayan acid alfisol

Present investigation studied plant water relations and soil physical properties through AM fungi (Glomus mosseae) to mitigate drought stress in Himalayan acid Alfisol having low water retentivity. Experimentation was carried out at Palampur, India during 2009–2011 in okra–pea cropping system in randomized block design (RBD) replicated thrice with 14 treatments comprising arbuscular mycorrhizal (AM) fungi, varying phosphorus nutrition and irrigation regimes at 40 and 80% available water holding capacity. Integrated use of AM fungi at varying phosphorus (P) levels and irrigation regimes led to significantly higher relative leaf water content (3% each) in okra and pea besides significantly higher xylem water potential (27%) in pea over non-AM fungi counterparts. AM fungi enhanced water-use-efficiency in okra (5–17%) and pea (12–35%) over non–AM fungi counterparts. AM fungi also improved water holding capacity (5–6%) and mean weight diameter of soil particles (4–9%) over non–AM fungi counterparts; but, had nominal or no effect on bulk density. Mycorrhizal plants maintained higher tissue water content imparting greater drought resistance to plants over non–mycorrhizal plants at moisture stress. It is inferred that integrated application of AM fungi and P at varying irrigation regimes improved the plant water relations vis-à-vis drought resistance, crop productivity, WUE, soil aggregation and water holding capacity in okra–pea sequence in Himalayan acid Alfisol.     

Growth Behavior,Nitrogen-Form Effects on Phosphorus Acquisition,and Phosphorus–Zinc Interactions in Brassica Cultivars under Phosphorus-Stress Environment

Phosphorus (P) and zinc (Zn) interact both in plants and soils and hence may affect the availability and utilization of each other. To investigate P and Zn nutritional status and P–Zn interactions, two genetically diverse Brassica cultivars classified as P tolerant (Brown Raya) and P sensitive (Sultan Raya) were grown in a sand-based pot culture. Jordan rock phosphate (RP) and monocalcium phosphate [Ca(H₂PO₄)₂] were used as P sources, and ammonium nitrate (NH₄NO₃) or nitrate (NO₃ ^--) only were used as nitrogen (N) sources. Two Zn levels [0.25 (low Zn) and 2.5 (high Zn) mg zinc sulfate (ZnSO₄·5H₂O) kg^?1 sand, respectively] were applied along with recommended doses of other essential nutrients in the culture media. Cultivars differed significantly for their response to added P for biomass accumulation, but Zn supply had little effect. Cultivar Brown Raya had greater P uptake and P-utilization efficiency (PUE) than Sultan Raya under a P-stress environment, irrespective of Zn and N supply. Zinc supply had little effect on tissue P concentration and P uptake per unit of root dry matter (RDM) in either cultivar, irrespective of N supply. An increase in P supply caused a significant reduction in specific Zn uptake (Zn uptake per unit of RDM; SZnU) and tissue Zn concentration of both cultivars. The reduction in tissue Zn concentration cannot be ascribed entirely to a dilution effect. Zinc concentrations and uptake by P-efficient cultivar Brown Raya were significantly lower and more sensitive to P uptake than those of P-sensitive Sultan Raya cultivar. It is suggested that high PUE may depress plant Zn uptake and therefore cause a reduction in Zn concentration of Brassica grown in low-P and possibly low-Zn soils. In NH₄NO₃ nutrition, plants had significantly lower cation concentrations compared to NO₃ ^-- nutrition only. Brown Raya consistently had lower cation concentrations than Sultan Raya under P stress. The differences in cation concentrations decreased with increased P availability, but Zn supply had no significant effect. In Brown Raya, the ratio of potassium in roots to shoots was always greater than in Sultan Raya. This suggested that lower cation concentrations in Brown Raya were due to root carboxylate exudations, which in turn were related to better P acquisition and PUE under insufficiently buffered P-stress environment.     

Behaviour of Potassium and Trace Elements in Rhizosphere of Flue-Cured Tobacco (Nicotiana Tabacum L.)

The study on the behaviour of potassium,phosphate and trace elements,Fe,Mn,Cu and Zn,in the rhizosphere of different varieties of flue-cured tobacco (Nicotiana tabacum L.)with high and low potassium application rate with rhizobag technique showed that soil available K,soil available P,and slow available K was in depletion status,whereas DTPA extractable Fe,Mn,Zn and Cu accumulated obviously in rhizosphere.The depletion and accumulation rates of mineral nutrients differed in degree with K application rate,soil type,and tobacco variety.The content of available K in both rhizosphere and bulk soil and K concentration in tobacco leaf increased significantly,and the available P in rhizosphere dropped with more K application.The DTPA-Fe content of red soil much lower in pH was higher than that of calcareous soil in bulk soil.But the DTPA-Fe content of calcareous soil was much higher than that of red soil in rhizosphere,which was considered perhaps to be mainly related to releasing of Fe phytosiderophore.Nitrate coule increase depletion of a vailable K in rhizosphere and also soil pH in comparision with ammonium.     

Contribution of Roots and Mycorrhizal Hyphae on Phosphorus Efficiency of Maize (Zea mays,L.) Genotypes Grown on Calcareous Soil—A Mechanistic Modeling Approach

ABSTRACT

This work was conducted to study phosphorus (P) efficiency of two maize genotypes (Zea mays, L.) in calcareous soil grown in potted soil with two levels of P in soil by adding 40 and 270 mg P/kg soil. Half of the pots were inoculated with arbuscular mycorrhizal fungi (AMF) (Rhizoglomus irregulare). The maize genotypes were harvested two times at 35 and 50 days after transplanting. The plant dry matter, root length and Plant P uptake of maize genotype Hagen 1 without mycorrhizal fungi (AMF) increased significantly compared with Hagen 9 at a low P level. In contrast, there was no significant difference between two maize genotypes inoculated with AMF under the same P level. The predicted value increased rapidly with increasing P levels from about 70% up to 97% in both maize genotypes with and without mycorrhizal fungi. At a low P level, the mycorrhizae hyphae contributed by about 31.6% and 30.2% of the predicted total P uptake in maize genotype Hagen 1 and Hagen 9, respectively. The results of this study suggested that the P-inefficient genotype Hagen 9 improved with inoculation with mycorrhizal fungi under a low P level at the same conditions of this experiment. Also, root growth system and mycorrhizal hyphae length would be a suitable plant parameter for studying P efficient maize genotypes, especially under limited P supply. The current study clearly pointed out that the mechanistic simulation model (NST 3.0) provides useful tools for studying the role of AMF in P uptake of plant.     

Comparison of volatile constituents of Persicaria odorata(Lour.) Soják (Polygonum odoratum Lour.) and Persicaria hydropiper L. Spach (Polygonum hydropiper L.)

Polygonum odoratum Lour. has been reclassified as Persicaria odorata (Lour.) Soják [Wilson, K. L. Polygonum sensu lato (Polygonaceae) in Australia. Telopea 1988, 3, 177-182]; other synonyms currently used are Vietnamese mint or Vietnamese coriander and, in Malaysia, Daun Laksa or Laksa plant. The aerial parts of Laksa plant are highly aromatic, and they contain many organic compounds such as (Z)-3-hexenal, (Z)-3-hexenol, decanal, undecanal, and dodecanal that are typical for green, citrus, orange peel, and coriander odors. In addition to these aldehydes, 3-sulfanyl-hexanal and 3-sulfanyl-hexan-1-ol were discovered for the first time in this herb. The fresh leaves are pungent when they are chewed, although the active compound has never been identified. The pungency of Persicaria hydropiper (L.) Spach (formerly Polygonum hydropiper L., synonym water pepper) is produced by polygodial, a 1,4-dialdehyde derived from drimane terpenoids. We also identified polygodial as the active pungent compound in P. odorata (Lour.) Soják.     

Nitrogen and Phosphorus Flows in the Finnish Agricultural and Forest Sectors, 1910–2000

An assessment of the environmental quality of sediments at several locations of the Ría de Pontevedra (NW of Spain) was performed by integrating toxicity data obtained from multiespecies bioassays, chemical data from analysis of mussels and sediment, and physical–chemical parameters of the sampled sites. Subsequently, a toxicity identification evaluation (TIE) method intended for characterization and identification of the toxic agents was applied to the most polluted location by using the Paracentrotus lividus sea urchin bioassay. Both metals and organic compounds seem to be the causative agents of toxicity in elutriates of the studied sediment. Finally, multivariate statistics were applied for a better interpretation of results. A factor analysis was developed to establish the relationship among variables and to derive local sediment quality guidelines (SQG) by linking chemical contamination to biological effects. When multidimensional scaling and cluster analysis were performed to group the locations according to either the chemistry or toxicity data, P3-site was always clearly broken up the others. The different approaches all supported the same conclusion: site P3 can be considered highly contaminated by both trace metals and PAHs resulting in high toxicity for all the tested species.     

Effect of different safflower (Carthamus tinctorius L.)–bean (Phaseolus vulgaris L.) intercropping patterns on growth and yield under weedy and weed-free conditions

Two field experiments were carried out over two consecutive years (2010–2011) in the research field of the College of Agriculture, Shiraz University, Fars Province, southern Iran. The study was a factorial experiment based on a randomized complete block design with three replications: the first factor was the ratio of safflower (Carthamus tinctorius L. Pi cv.) to bean (Phaseolus vulgaris L. Saiad cv.) at five levels (safflower and bean sole cropping, and intercropping of safflower and bean at ratios of 1:3, 2:2 and 3:1); and the second factor was weed management at two levels: weed-free (complete weed control) and weedy (no weed control). The results showed that an intercropping system was the most appropriate method for decreasing the adverse effect of weeds on the performance of both crops. Intercropping was more suitable for weedy than weed-free conditions. According to the land equivalent ratio (LER) value, if the main crop was bean, the best intercropping treatment was one row of safflower and six rows of bean (S₁B₃) under both weedy and weed-free conditions. By contrast, if the main crop was safflower, the best treatment under weedy conditions was S₁B₃, whereas under weed-free conditions the best treatment was two rows of safflower and four rows of bean (S₂B₂). Overall, S₁B₃ can be introduced as the best intercropping method.     

Heavy Metals, Phosphorus and Some Other Elements in UrbanSoils of Hangzhou City, China

Health implications of inhaling and/or ingesting dust particles with high concentrations of heavy metals from urbansoils are a subject of intense concern. Understanding the geochemistry of these metals is key to their effective management. Total concentrations of heavy metals, phosphorus (P) and 8 other elements from topsoil samples collected at 82locations in Hangzhou City were measured to:a) assess their distribution in urban environments;and b) understand theirdifferentiation as related to land use. Metal mobility was also studied using a three-step sequential chemical fractionationprocedure. About 8.5%, 1.2%, 3.6%, 11.0% and 30.3% of the soil samples had Cd, Cr, Cu, Pb, and Zn concentrations,respectively, above their allowable limits for public and private green areas and residential use. However, in commercialand industrial areas, most samples had metal concentrations below their allowable limits. Statistical analyses revealedthat the 16 measured elements in urban soils could be divided into four groups based on natural or anthropic sourcesusing a hierarchical cluster analysis. Additionally, Cu, Pb, and P showed similar spatial distributions with significantpollution in commercial zones, suggesting vehicle traffic or commercial activities as dominant pollutant sources. Also, Cd,Co, Cr, Ni, Zn, Mn and Fe had the highest concentrations in industrial locations, signifying that industrial activities werethe main sources of these seven metals. Moreover, the data highlighted land-use as a major influence on heavy metalconcentrations and forms found in topsoils with large proportions of soil Cd, Co, Cr, and Ni found in residual fractionsand soil Cu, Pb and Zn mainly as extractable fractions.     

New oilseed rape (Brassica napus L.) varieties – canopy development,yield components,and plant density

Full exploitation of the potential of new varieties requires research, whose aim is to adapt the technology to their needs. A two-factor experiment evaluated the effect of row spacing (33, 44, and 55 cm) of three oilseed rape (OSR) varieties (conventional, hybrid, and “semi-dwarf” hybrid variety) on canopy area index (CAI) and yield components. At higher row spacing, OSR plants were characterized by a strong increase in the CAI at successive growth stages; thereby, the incomplete use of production area was compensated at the pod development stage. The differences in the CAI between row spacings were significant until the end of flowering, whereas differences in the CAI between varieties were significant until the flower bud development stage. In the next development phases, CAI of OSR plants was at a similar level to all plots. However, the statistical analysis showed a declining trend in seed yield and yield biomass (pods and straw weight) with increasing row spacing. A positive aspect of increased row spacing was a decrease in glucosinolates content in seeds. The differences in fat content were statistically insignificant. The hybrid varieties of OSR produced the highest seed yield at a row spacing of 33 cm, while the conventional – at a row spacing of 44 cm. These relationships are confirmed by high positive correlations of seed weight and pod weight per unit area with CAI. The results have important practical aspect, because it shows that it is possible to reduce the number of OSR plants per unit area, thereby reducing demand for expensive certified seeds for sowing but to certain limits. Too small plant density binds to the risk of decreased seed yield. It may be justified, e.g., in extensive or organic farming where wide row creates the possibility of mechanical weed control.     

Effect of Organic Manure and Crop Residue Based Long-Term Nutrient Management Systems on Soil Quality Changes under Sole Finger Millet (Eleusine coracana (L.) Gaertn.) and Groundnut (Arachis hypogaea L.) – Finger Millet Rotation in Rainfed Alfisol

A long-term experiment was conducted to evaluate the effect of integrated use of organic and inorganic sources of nutrients on soil quality and its relation to finger millet yield under two predominant crop rotations viz., groundnut–finger millet and finger millet monocropping in hot moist semiarid rainfed Alfisol soils in South India. Two experiments were laid out separately for each cropping system in a randomized complete block design with five treatments individually with FYM and maize residue-based combinations viz., Control (T1), FYM @ 10t ha ^?1 or Maize residue (MR) @ 5t ha ^?1 (T2), farm yard manure (FYM) @ 10t ha ^?1 or Maize residue (MR) @ 5t ha ^?1 + 50% RDF (Recommended Fertiliser Dose) N, P₂O₅ &; K₂O (T3), FYM @ 10t ha ^?1 or Maize residue (MR) @ 5t ha ^?1 + 100% RDF N,P₂O₅ &; K₂O (T4), Recommended N, P₂O₅ &; K₂O (T5). Thus, four sets of nutrient management systems were evaluated. The results showed that farm yard manure or maize residue application in combination with recommended dose of fertilizer significantly improved the soil physical, chemical, and biological properties compared to control and application of inorganic fertilizers alone. Based on evaluation of 19 soil quality parameters under each of the four nutrient management systems, the common key soil quality indicators emerged out were: organic C (OC), available nitrogen (N), available sulfur (S), and mean weight diameter (MWD) of soil aggregates. A significant correlation between the finger millet yield and the relative soil quality indices (RSQI) indicates the importance of soil quality in these semiarid Alfisol soils. The results and the methodology adopted in the present study could be of importance in improving the soil quality not only for the region of the study, but also in other identical soils and cropping systems across the world.     

Effect of seed‐placed fertilizer on the emergence (germination) of soybeans (Glycine max L.) and snapbeans (Phaseolus vulgaris L.)

Abstract

Field trials were established on a loamy fine sand and a silt loam using snapbeans and soybeans as test crops, respectively. Row fertilizer was placed with the seed (seed‐placed). Treatments were arranged in a 3×3×3 factorial experiment, and N, P, and K were applied in all combinations at three rates (0, 3.4, and 6.8 kg/ha). Ammonium nitrate (AN), monoammonium phosphate (MAP), concentrated superphosphate (CSP) and potassium chloride (KCl) were used as sources of N, P and K. Additional treatments compared MAP with diammonium phosphate (DAP) and KCl with potassium nitrate (KNO₃).

The salt index of each treatment was inversely related to emergence, i.e. as the salt index increased, the emergence decreased. Level of N was more important than level of P or K in regards to reduction in emergence. Snapbeans grown on a loamy fine sand were extremely sensitive to damage from seed‐placed fertilizer, even at rates as low as 3.4 kg/ha of N, P or K. Soybeans planted on a silt loam soil were less sensitive than snapbeans planted on a loamy sand. The soybeans were able to tolerate up to 10.2 kg/ha of seed‐placed P plus K or 6.8 kg/ha of seed‐placed N plus P or N plus K without causing a significant delay in emergence.     

Analysis of volatile compounds of taperebá (Spondias mombin L.) and cajá (Spondias mombin L.) by simultaneous distillation and extraction (SDE) and solid phase microextraction (SPME)

Volatile compounds of cajá and taperebá fruits, both classified as Spondias mombin, but from different geographic origins, were extracted (and analyzed) using solid phase microextraction (SPME) and simultaneous distillation and extraction (SDE). Forty-eight compounds were identified in taperebá and 47 in cajá by SPME using a DVB/CAR/PMDS fiber. (E)-Caryophyllene (18.7%), ethyl butyrate (10.0%), and ethyl hexanoate (7.0%) were the most abundant components in taperebá volatiles extracted by SPME, whereas myrcene (41.1%) and beta-phellandrene (8.5%) were the major compounds in cajá. In the taperebá SDE extract, 46 substances were identified, and (Z)-caryophyllene (13.2%) and limonene (9.5%) were predominant. From the 42 substances found in the SDE extract of cajá, the major components were myrcene (38.0%) and p-cymene (6.2%). The two fruits showed similar chromatograms upon the use of SDE and SPME. These methods made it possible to determine 30 identical components in both fruits by using SDE and 32 by using SPME.     

Different Forms of Potassium and Their Contributions toward Potassium Uptake under Long-Term Maize (Zea mays L.)–Wheat (Triticum aestivum L.)–Cowpea (Vigna unguiculata L.) Rotation on an Inceptisol

In a long-term fertilizer experiment at the Indian Agricultural Research Institute, New Delhi, with maize, wheat, and cowpea, various forms of potassium (K) and their contribution toward K uptake were found to be affected by fertilizer use and intensive cropping. The treatments included for the study were a control, 100% nitrogen (N), 100% N–phosphorus (P), 50% NPK, 100% NPK, 100% NPK + farmyard manure (FYM at 15 t ha^?1 to maize only), and 150% NPK. The concentration of nonexchangeable K was greatest, followed by exchangeable K and water-soluble K. The study revealed no significant change in water-soluble K concentration in surface soil compared to N, NP, and control, indicating existence of an equilibrium between different K forms. Application of 100% NPK significantly increased water-soluble K concentration in surface soil compared to N, NP, and control treatments after maize, wheat, and cowpea. Application of NPK + FYM and 150% NPK resulted in greater quantities of all the K forms as compared to other treatments. Among the three forms, water-soluble K contributed predominantly to K uptake by maize and wheat; however, nonexchangeable K contributed significantly to K uptake by cowpea.     

Modified Soil‐Test Methods for Extractable Phosphorus in Acidic,Neutral, and Alkaline Soils

Abstract

Although numerous soil‐test methods for estimating extractable phosphorus (P) have been developed around the world, their results are difficult to compare because of the very different scale levels used. In the present study, the Bray–Kurtz method (Bray‐P) is used as a reference value. Two other methods [lactate‐P and sodium bicarbonate (NaHCO₃)‐P] were modified to facilitate the comparison of extractable‐P determinations, mainly by adjusting the shaking time. These three methods were applied to 101 soil samples from an extensive region of Argentina with soil pH values ranging from 5.5 to 8.5. The results confirm that the Bray‐P and the two modified methods (lactate‐P and NaHCO₃‐P) determine similar contents of extractable P but are not applicable to all types of soils and conditions. Equations that minimize the statistical error were selected for soil properties such as organic carbon (OC) content, pH, soluble salts, and calcium carbonate content. Correlation coefficients between Bray‐P and NaHCO₃‐P increased to 0.91 and 0.95 in soils with high and low OC levels, respectively. It was also demonstrated that the lactate‐P test is not suitable for soils rich in calcium carbonate or soluble salts. These two modified methods are expected to be useful for testing P values that impact agricultural production.     

Fe‐deficiency tolerance in papaya (Carica papaya L.): Ph reduction and chlorosis recovery in response to stress

The phenomenon of Fe‐stress response mechanism was examined using papaya as a test fruit plant species. This plant behaved like the many Fe‐efficient crop cultivars, reduced the pH of the minus Fe nutrient medium, followed by recovery from chlorosis. The response mechanism was observed in both the 2 cultivars, CO‐1 and CO‐3. Evidence obtained with this plant supports the widespread occurrence of the mechanism in diverse crop species ‐ grain, vegetable and fruit crop plants too.     

Changes in Nitrogen,Phosphorus, and Potassium in a Long‐Term Continuous Maize–Wheat Cropping System in India

In a long‐term maize–wheat rotation at the Punjab Agricultural University, Ludhiana, India (subtropical climate), the effects of nitrogen (N), phosphorus (P), and potassium (K) addition on soil fertility and forms of inorganic P and K in the plow layer of an alkaline sandy loam soil were measured after 11 and 22 years of cropping. The treatments comprised four rates of N (0, 60, 120, and 180 kg N ha^?1) as urea, three rates of P (0, 17.5, and 35 kg P ha^?1) as single superphosphate, and two rates of K (0 and 33 kg K ha^?1) as muriate of potash. The treatments selected for the present study were N₀P₀K₀, N₁₂₀P₀K₀, N₁₂₀P_17.5K₀, N₁₂₀P₃₅K₀, N₁₂₀P_17.5K₃₃, and N₁₂₀P₃₅K₃₃. A significant year × treatment interaction in decreasing available N [alkaline potassium permanganate (KMnO₄)–oxidizable N) status of soils was found in all the treatments. Available P (Olsen P) in the control plot decreased over time whereas in plots with added P, available P increased significantly after years 11 and 22, with the greatest increase in the N₁₂₀P_17.5K_o treatment. Compared to the initial values, continuous P fertilization resulted in greater total P and chloride P concentrations after 11 and 22 years. Although sodium hydroxide (NaOH) P and sulfuric acid (H₂SO₄) P increased in P‐treated plots from the start of the trial to year 11, they decreased from year 11 to year 22. Among these inorganic P forms, chloride P was significantly positively correlated with P uptake (r = 0.811*). When only N and P were applied, available K [ammonium acetate (NH₄OAc)–extractable K] significantly decreased over time. In plots without K addition, water‐soluble and exchangeable K decreased from their initial status. Compared to year 11, water‐soluble K increased, whereas exchangeable K decreased after year 22 in plots receiving no K fertilizer. Compared with NPK treatments, a significant decrease of total K in NP treatment plots suggests the release and uptake of nonexchangeable K. Water‐soluble K and exchangeable K were not correlated with K uptake. These results suggest that long‐term application of P fertilizers resulted in the accumulation of P in the soil, which could have resulted in saturation of P binding sites. Of the soil inorganic P fractions, only chloride P appears to be a good indicator of plant‐available P. The gradual loss in native soil K and release of nonexchangeable K indicates the need for adding K fertilizer to maintain soil fertility.