Olga Susana Heredia

Efecto de diferentes técnicas de manejo de residuos de la cosecha forestal en algunas propiedades de un suelo Kandiudult en el Noreste argentino

El objetivo de este trabajo fue evaluar el efecto de diferentes tecnicas de manejo de residuos de Pinus ellioti Engelm en indices de calidad de suelo en un Kandiudult de Misiones, Argentina, en condiciones de altas temperaturas y precipitaciones. Los tratamientos fueron: T1) extraccion manual de los residuos y reforestacion; T2) quema y reforestacion; T3) conservacion de los residuos y reforestacion; T4) conservacion de los residuos y desarrollo de bosque secundario. El diseno estadistico fue en bloques completamente al azar con cuatro repeticiones, en bloques de 840 m2. Las muestras de suelo fueron extraidas un ano y medio despues de implantados los tratamientos, por ser importante el monitoreo a corto plazo, dado que los cuatro primeros anos son clave en las plantaciones de pinos en esta region . La remocion total de los residuos se tradujo en menores valores de las formas de carbono total (Ct) (P < 0,05). La quema, a corto plazo, produjo un aumento significativo de fosforo extractable (Pe) (P < 0,05). La conservacion de los residuos provoco un aumento significativo de nitrogeno total (Nt), equivalente al de la quema, y valores mas altos de carbono total (Ct) y carbono liviano (Cl) (P < 0,05).

ANTHROPOGENIC EFFECT ON SOIL ORGANIC PHOSPHORUS FRACTIONS IN TROPICAL ECOSYSTEMS

Total organic phosphorus (P), labile organic P, and total carbon were determined in composite surface soil samples, with three replicates, in a Kandihumult from Misiones province, Argentina. The analysis was performed on <0.1 mm, 2–0.5 mm, and >8 mm aggregate fractions obtained by dry sieving. Representative situations were selected to evaluate changes in P dynamics by soil use: a native subtropical forest, a degraded agroecosystem with a 50-year yerba mate plantation (Ilex paraguariensis Saint Hill.), and a similar plantation with a 6-year associated elephant grass (Pennisetum purpureum Schumach). Native pristine soil from the forest presented the highest content of phosphorus in more humified fractions (<0.1 mm). Fifty-year cultivation of “yerba mate” produced a degraded agroecosystem with 10% decrease of total organic phosphorus forms in humified fractions. Six-year-old elephant grass mulch incorporation increased total organic phosphorus both in more humified fractions and in macroaggregates (>8 mm), due to addition of decomposable organic materials. Labile organic phosphorus was higher under stress conditions.

Phosphorus sustainability in tropical ecosystems

Highly weathered soils in the tropics display nutrient deficiencies, especially of phosphorus (P) in low-activity clay soils. The objective of this work is to evaluate P distribution in soil fractions (> 8 mm, 2–8 mm, 0.25–2 mm, 0.10–0.25 mm, < 0.10 mm) and to study the effect of management practices on P sustainability and availability. Surface and subsurface soil samples were taken from three different situations: virgin soil, degraded plantation of Ilex paraguariensis Saint Hil. (yerba mate), and a similar plantation consociated with Pennisetum purpureum Schumach (elephant grass), used as a mulch. For virgin soils, the highest P values were present in the 8 mm fractions; macroaggregates P is associated with decomposable material which is related to short-term fertility. Its beneficial action was also observed below the soil surface. Protecting the soil with mulch improved P sustainability in ‘yerba mate’ agroecosystems.

Yield components and their relationship with total and extractable foliar phosphorus in soybean

Abstract Six soybean cultivars (maturity group V) were sown in a Typic Argiudoll. Experimental plots were arranged in a randomized block design with three replications. Sampling dates were at different stages: R2, R4, and R5. Two foliar phosphorus (P) forms were determined: total P (TP) and dilute acetic acid‐extractable P (DAEP) which correlated with each other and with some yield components. At the R2 stage, there was a good correlation with node number in the R5 stage and TP, DAEP, and petioles‐DAEP. Weight of 1000 grains was asssociated with foliar P measured later in the R4 and R5 stages.