Phosphorus fractions and dynamics as affected by land-use changes in the Central Mexican highlands

Land-use change from forest to agriculture in the volcanic ash-derived soils of Mexico has increased over recent decades. It is likely that land uses and management practices, particularly fertilizer use have affected phosphorus (P) distribution and availability. The objective of this study was to evaluate the effects of land-use types (native forest and maize mono-cropping), and the related P addition, on the forms and distribution of soil P and their isotopic exchangeability. An Andisol, sampled from a cropping site, along with the contiguous area under native forest was treated with ³²P-labelled potassium phosphate (KH₂³²PO₄). The soil samples were extracted after incubation times of 7, 21, 35 and 49 days. Phosphorus content and ³²P recovery in fractions sequentially extracted were assessed for each incubation time. Total soil P was dominated by inorganic fractions (79 to 86%) in both land-use types. Resin-Pi, bicarbonate extractable inorganic P (Bic-Pi) and sodium hydroxide extractable inorganic P (NaOH_0.1-Pi) were all raised with P addition. However, the proportion of organic P fraction was reduced under cropped soil. The recovery of ³²P in soils with P addition indicates that resin-Pi, Bic-Pi and NaOH_0.1-Pi comprised nearly all the exchangeable P. In native soils with no P addition, more than 19% of the ³²P was recovered in Bic-Po and NaOH_0.1-Po forms. This finding indicates that organic P cycling is crucial when soil Pi reserves are presented in an inadequate amount. Ecologically based management has to be designed for replenishment and succeeding maintenance of soil organic P compounds to increase sustainable agricultural production.     

Tracer methods to assess nutrient uptake distribution in multistrata agroforestry systems

Separate assessment of nutrient uptake by individual plants in mixed cropping with trees is impossible without tracer techniques. The different ¹⁵N-to-¹⁴N isotope ratio of atmospheric and soil N can be used to study the contribution of biologically fixed N to the nutrition of associated trees. In most cases, the assessment of nutrient uptake distribution is an appropriate way of evaluating how to improve the transfer of biologically fixed N. Radioisotopes (e.g., ³²P), stable isotopes (e.g., ¹⁵N) and rare elements (e.g., Sr) can be used to determine relative root activity distribution by applying the tracer to different soil depths or distances from trees. A broadcast application of the tracer instead of point application makes it possibe to calculate uptake values per unit area. The direct determination of nutrient pathways with such robust experiments offers considerable advantages for improving nutrient use efficiency and complementarity in multistrata agroforestry systems. This revised version was published online in June 2006 with corrections to the Cover Date.     

The agronomic benefit of phosphate rock application with elemental sulfur depends on the reactivity and fertilizer placement

Abstract

A possible way to improve phosphate rock (PR) agronomic performance is through the addition of elemental sulfur (S⁰). We used ³²P isotope dilution method to assess the P taken up by crops treated with PR. Two experiments, one with common bean and other with upland rice, were carried out, to evaluate the effect of S⁰ on the agronomic performance of two contrasting PR, applied in different methods. Gafsa (GPR) and Patos de Minas (PPR) were used as the high and low reactivity PR, respectively. The experiments were arranged in completely randomized design on factorial structure 2?×?2 × 2?+?2; which means 2 PR (GPR and PPR) versus 2?S⁰ condition (with or without-S⁰) versus 2 application methods (band and broadcast) plus 2 additional treatments (control and triple superphosphate). In band application the S⁰ increased the amount of P uptake by plants from fertilizer of GPR from 2.57 to 9.86?mg pot^?1 for common bean and of 2.26 to 7.05?mg pot^?1 to rice. Regardless the management adopted, less than 2% of P applied as PPR has been taken up by crops. The addition of S⁰ as a strategy to increase the agronomic performance of PR is PR characteristics dependent and fertilizers placement.     

BORON UPTAKE AND DISTRIBUTION IN FIELD GROWN CITRUS TREES

In low fertility tropical soils, boron (B) deficiency impairs fruit production. However, little information is available on the efficiency of nutrient application and use by trees. Therefore, this work verified the effects of soil and foliar applications of boron in a commercial citrus orchard. An experiment was conducted with fertigated 4-year-old ‘Valencia’ sweet orange trees on ‘Swingle’ citrumelo rootstock. Boron (isotopically-enriched ¹⁰B) was supplied to trees once or twice in the growing season, either dripped in the soil or sprayed on the leaves. Trees were sampled at different periods and separated into different parts for total B contents and ¹⁰B/¹¹B isotope ratios analyses. Soil B applied via fertigation was more efficient than foliar application for the organs grown after the B fertilization. Recovery of labeled B by fruits was 21% for fertigation and 7% for foliar application. Residual effects of nutrient application in the grove were observed in the year after labeled fertilizer application, which greater proportions derived from the soil supply.     

Prevalence of Giardia intestinalis infection in dogs of breeding kennels in Japan

Giardia intestinalis antigen in fecal samples was examined in 361 dogs of 14 breeding kennels located at various areas in Japan, using a commercial enzyme-linked immunosorbent assay (ELISA) kit. G. intestinalis antigen was detected in 37.4% of the fecal specimens. All of the 14 breeding kennels were positive for G. intestinalis antigen with the range from 6.7 to 59.3%. The prevalence in puppies (54.5%) was significantly (p < 0.01) higher than that in adults (30.9%). There was no difference in prevalence between males and females, and between the puppies from the mother dogs positive and negative for Giardia antigen. In conclusion, G. intestinalis widely invaded the breeding kennels in Japan.     

Effects of companion crops and tillage on soil phosphorus in a Brazilian oxisol: a chemical and 31P NMR spectroscopy study

Journal of Soils and Sediments - Phosphorus (P) is often the main limiting factor for plant growth in highly weathered tropical soils. Phosphate use efficiency and crop yields could be increased in...     

Nitrogen transfer from green manure to organic cherry tomato in a greenhouse intercropping system

Abstract

This work aimed to evaluate the nitrogen transfer, the yield and the nutrient contents of organic cherry tomatoes intercropped with legumes in two successive years. The randomized block experimental design was used with eight treatments and five replicates, as follows: two controls with single cherry tomato crop (with and without corn straw cover); cherry tomato intercropped with jack bean (Canavalia ensiformis DC); white lupine (Lupinus albus L.); sunn hemp (Crotalaria juncea L.); velvet bean-dwarf [(Mucuna deeringiana (Bort) Merrill)]; mung bean (Vigna radiata (L.) Wilczek), and cowpea (Vigna unguiculata (L.) Walp). The number of total fruits, the weight of total fruit and an average weight of the total fruit in the first year was 25%, 33% and 13% higher than the second-year, respectively. The lower N-content of cherry tomato leaves in the treatment with mung bean can be reflected of lower %N transfer of cherry tomato leaves in the same treatment compared to treatment with cowpea bean. The N-content and %N transfer of cherry tomato leaves was 50 and 42% higher in year 1 than in year 2, successively. Nevertheless, in general, the legumes used in this study contributed equally in the N transfer to the cherry tomato plants. The P, K, Mg, Ca, Cu, Mn, Fe and Zn content in the leaf and shoot were no difference between the treatments. However, the Mg, Ca, Cu, Fe, Mn and Zn content of the leaf were higher in year 2 than year 1.     

Bacterial communities associated with nodal roots of rice plants along with the growth stages: Estimation by PCR-DGGE and sequence analyses

Bacterial communities in rice roots that developed from different nodes and at different growth stages were compared by using polymerase chain reaction (PCR)-denaturing gradient gel electrophoresis (DGGE) analysis of 16S rDNA. Rice root samples were collected at three stages, namely tillering (July 2), maximum tillering (July 21), and ripening (September 12). The bacterial diversity in rice roots was found to increase along with the growth stages of the rice plants as well as the root age from the numbers of DGGE bands. The community structure of the bacteria was also found to change with the growth stages and root age from cluster analysis. Sequence analysis of the DGGE bands indicated that the dominant bacteria associated with rice roots were Gram-negative bacteria, especially β-Proteobacteria irrespective of the growth stages and root age. DGGE bands related to Janthinobacterium agaricidamnosum W1r3T and Clostridium sp. FCB90-3 were ubiquitous in many roots irrespective to the sampling date. Principal component analysis enabled to characterize the DGGE bands related to nitrogen-fixing Azoarcus spp., and Azovibrio sp. BS20-3 in the samples collected on July 2 and on July 21, and the myxobacteria collected on September 12, respectively, as representative bacteria in the bacterial communities. The habitat around older rice roots at every sampling date was more reductive than that around younger rice roots, and the DGGE bands related to Spirochaeta spp. were specific in older roots at every sampling date. Some specific bacteria that were most closely related to the DGGE bands were found from principal component analysis to characterize young and old. roots at each growth stage as follows: aerobes Flavobacterium sp. 90 clone 2 and Janthinobacterium agaricidamnosus W1r3T in young roots and facultative anaerobes Dechloromonas sp. MissR and Anaeromyxobacter dehalogenans 2CP-3 in old nodal roots on July 2, strict anaerobe Geobacter pelophilus Dfr2 and aerobes Nitrosospira sp. Nsp17 and uncultured Nitrospira sp. clone 4-1 in old roots on July 21, and different Clostridium spp. in both young and old roots and Desulfovibrio magneticus RS-1 in old roots on September 12, respectively. A larger number of the closest relatives of anaerobic bacteria grew at the late stage than at the early stages, and in old roots than in younger roots. Thus, the environment of paddy roots was remarkably heterogeneous as a bacterial habitat, where not only the whole root system but also a root may create oxic and anoxic environments.     

Erratum to: Biomass and nutrient accumulation by cover crops and upland rice grown in succession under no-tillage system as affected by nitrogen fertilizer rate

Journal of Crop Science and Biotechnology - Due to an unfortunate oversight the author’s name and affiliation have been given erroneously. It should be read: