Sunday, 9 July 2006

Use of Nuclear Techniques to Evaluate Management Practices for Improving Soil Fertility and Sustainable Common Bean Production in Acid Soil.

A. Garcia1, G. Hernandez1, A. Nuviola1, G. Duenas1, G. Herrero2, S. Curbelo3, J. L. Reyes3, and J. J. Drevon4. (1) Soil Institute, Havana, Cuba, (2) Ecology and Systematic Institute, Havana, Cuba, (3) Experimental Station, Pinar del Rio, Cuba, (4) Institute National de Recherche Agronomique (INRA), Montpellier, France

Laboratory, glasshouse and field experiments were carried out to evaluate selected management practices such as the use of phosphate rock based products and soil liming, for improving soil fertility and sustainable common bean production in an acid Acrisol soil of Cuba. In laboratory experiment the effectiveness of the indigenous Trinidad de Guedes phosphate rock (PR) and partially acidulated PR (FPA 50) were evaluated as P sources for increasing phosphorus soil status using the Isotopic Exchangeable Kinetic (IEK) method. The 32P labelled solution (1 ml of 32PO43- carrier-free solution with an activity included between 0,1 a1 MBq) was added to soil suspension at time zero and mixed thoroughly. At times = 1, 10 and 100 minutes, a volume of soil solution was removed with a polyethylene syringe and the solution was separated immediately from the solid phase using a millipore filtration system. In glasshouse, using the isotopic dilution method (ID), and in field experiments was evaluated the agronomic effectiveness of the above mentioned P sources for common bean genotypes, BAT 477, DOR 364, DOR 390 and Censa. In glasshouse experiment the 32P activity applied per pot containing 1,4 kg of soil was 2,96 MBq + 2 mg P kg-1. Another experiment was carried out in field to evaluate the effect of soil liming on grain yield and biological nitrogen fixation (BNF), using the ID method, of BAT 58, BAT 304, BAT 477, DOR 364, DOR 390, Judía Roja Camagüeyana (JRC) and Censa common bean genotypes. NN A285, a non-nodulating (non-fixing) common bean genotype was used as reference crop. The applied doses and enrichments of the 15N-tagged fertilizer were 50 kg N ha-1 as urea 2,5 at. % 15N excess and 15 kg N ha-1 as urea 5 at. % 15N excess to the reference (non-fixing) and fixing crops, respectively. In the laboratory experiment the results obtained showed that all P treatments increased P concentration in soil solution and the isotopically exchangeable P according the degree of solubilization of each P source. In the glasshouse experiment the results obtained revealed that there were genotypes differences in P uptake and in the use of P coming from the P sources, establishing a significant genotype effect on the effectiveness of P sources. On the average for the genotypes studied between 1,0 and 2,9 kg of P as FPA 50 (PAPR) was equivalent to 1 kg of P as SS. In the field experiments single super phosphate and the partially acidulated phosphate rock, FPA 50 increased grain yields over PR and control (without P) treatments. The soil liming increased grain yields and BNF of common bean genotypes over unlimed soil. On the average for the genotypes studied the fraction of nitrogen derived from air (Ndda) increased from 26,7% in unlimed soil to 37,8% in limed soil. They were identified common bean genotypes with higher values of Ndda in unlimed soil (>30%). The results obtained are useful for breeding programs aiming at obtaining common bean genotypes with high P use efficiency for areas having P deficient soils where low-cost P sources of medium solubility (FPA 50) can be applied.

Keywords: isotopic exchange kinetic, isotopic dilution method, 32P, 15N, genotype, phosphate rock, partially acidulated phosphate rock, single super phosphate

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