Phosphorus Use Efficiency in \u3cem\u3eLotus\u3c/em\u3e spp. under Contrasting Levels of Water Availability: A Comparison of Pot and Field Measurements

The results of the phosphorus (P) use efficiency measurements in pot experiments with soil as subtratum are controversial because they may not be representative of an equivalent situation under field conditions. Under P-stress conditions, strategies for improving phosphorus-use efficiency are: (1) increase the root surface soil contact area by modifying root morphology; (2) increase the effective root area by root symbiosis with arbuscular mycorrhizal fungi; (3) increase nutrient availability through rhizosphere modification. The level of water availability and P supply are of high interest because the water stress, which limits growth more than any other environmental factor, can be minimized by improving the supply of P. P use efficiency (PUE) depends on the internal capacity of individual species to produce more DM from a given amount of P absorbed, and an external efficiency which enables the plant to yield more due to an increased ability to extract P (phosphorus absorption efficiency, PAE) from the soil (Trolove et al. 1996). Because of the deep root of Lotus species in may be difficult to evaluate L. corniculatus and L. tenuis in pots. To examine the value of pot experiments to assess the phosphorus use efficiency of L. corniculatus and L. tenuis grown in a Vertisol, we compare responses under two contrasting levels of water availability and phosphorus supply, obtained in both pot and field conditions, for their consistency or discrepancy in order to determine the actual value of the pot results

Indicadores de calidad de la materia org\ue1nica del suelo en un Andisol cultivado

Agricultural practices influence the dynamics of soil organic matter (MOS) and its fractions. In this study, the following labile fractions of soil organic matter were determined: free light fraction (FLL), intra-aggregate light fraction (FLI), microbial biomass and mineralized C-CO2, on volcanic soil with different rotations, and later their use was evaluated as biological indicators of the impact of agricultural practices on the soil. The study was carried out in an eight year field experiment, with different productive systems (rotations) in a randomized complete block design. The free light fraction (FLL) was determined by density fractionation with NaI (1.8 g cm-3), and the intra-aggregate light fraction (FLI) was obtained by sonication (1,500 J s-1). Microbial biomass was quantified using the chloroform fumigation-incubation (FI) technique, and the basal soil respiration (C-CO2 evolution) was determined by incubation for a 10-day period. Increased soil use intensity decreased (P 64 0.05) C and N FLL contents, from 1.69 g C-FLL kg-1 soil (5-year rotation with alfalfa, Medicago sativa L.), to 0.49 g C-FLL kg-1 (annual crop rotation). However, these contents in FLI did not show a clear and consistent tendency (P 64 0.05). Soil biomass C and N decreased (P 64 0.05) with higher soil use intensity, from 551 to 264 \u3bcg C-CO2 g soil-1 and from 106 to 35 \u3bcg N-(NO3- + NH4+) g soil-1, respectively. The three studied indices were appropriate indicators to determine changes in soil organic matter quality as a result of agricultural practices.El manejo agron\uf3mico influye en ladin\ue1mica de la materia org\ue1nica del suelo (MOS) y sus diferentes fracciones. En este estudio se determinaron fracciones activas de la MOS: fracci\uf3n liviana libre (FLL), fracci\uf3n liviana intraagregados (FLI), biomasa microbiana y C-CO2 mineralizado, en un suelo volc\ue1nico cultivado con distintas rotaciones, y posteriormente se evalu\uf3 su uso como indicadores biol\uf3gicos del impacto del manejo agron\uf3mico en el suelo. El estudio se realiz\uf3 en un experimento de campo de ocho a\uf1os, con diferentes sistemas productivos (rotaciones) en un dise\uf1o de bloques completos al azar. La FLL fue determinada por fraccionamiento f\uedsico, usando NaI (1,8 g cm-3) y la FLI fue obtenida por sonicaci\uf3n (1.500 J s-1). La biomasa microbiana se cuantific\uf3 a trav\ue9s de fumigaci\uf3n-incubaci\uf3n (FI), y la respiraci\uf3n basal del suelo (evoluci\uf3n de C-CO2) por incubaci\uf3n durante 10 d\uedas. La rotaci\uf3n disminuy\uf3 (P 64 0,05) los contenidos de C y N de la FLL, de 1,69 g C-FLL kg-1 suelo (rotaci\uf3n con 5 a\uf1os de alfalfa, Medicago sativa L.) a 0,49 g C-FLL kg-1 de suelo (rotaci\uf3n con cultivos anuales). Sin embargo, estos contenidos en la FLI no mostraron una tendencia clara y consistente (P 64 0,05). La biomasa C y N, disminuyeron (P 64 0,05) con la mayor intensidad de uso del suelo, de 551 a 264 \u3bcg C-CO2 g suelo-1, y de 106 a 35 \u3bcg N-(NO3- + NH4+) g suelo-1, respectivamente. Los tres \uedndices estudiados representaron indicadores apropiados para determinar cambios en la calidad de la MOS producto del manejo agron\uf3mico

Productivity and Carbon Storage in Silvopastoral Systems with \u3cem\u3ePinus ponderosa\u3c/em\u3e and \u3cem\u3eTrifolium\u3c/em\u3e spp. Plantations and Pasture on a Volcanic Soil in the Chilean Patagonia

Little information is available about carbon (C) sequestration potentials in ecosystems on Andisols of the Chilean Patagonia. This study was undertaken to measure the size of the C stocks in three predominant ecosystems: Pinus ponderosa-based silvopastoral systems (SPS), pine plantations (PPP) and natural pasture (PST), and to examine how clover (Trifolium spp.) affect tree growth and stocks of soil C. The C contents of trees and pasture were determined by destructive sampling and dry combustion. Soil samples were taken at 0-5, 5-20, 20-40 cm depths in order to determine soil C and N. For PPP and SPS, respectively, 38.4 and 53.1 kg/tree of total tree C were stored aboveground, whereas 21.3 and 23.4 kg/tree were stored belowground. Tree diameter at breast height increased 1 and 2 cm/year in PPP and SPS, respectively, and was significantly higher in SPS, an interesting value for the region. Tree growth in SPS was enhanced by lower tree competition and the additional soil N provided by the leguminous pasture, resulting in larger amounts of C being sequestered. Soil organic C (SOC) stocks at 0-40 cm depth were 193.76, 177.10 and 149.25 Mg/ha in SPS, PST and PPP, respectively. The conversion of PPP to SPS and PST to PPP resulted in an increase of 44.51 Mg/ha and a decrease of 27.85 Mg/ha in SOC, respectively, at 0-40 cm soil depth. A favourable micro-climate (air temperature, soil moisture) has been observed in SPS as well as a synergistic effect between trees and pasture

Multiseason recoveries of organic and inorganic nitrogen-15 in tropical cropping systems

In tropical agroecosystems, limited N availability remains a major impediment to increasing yield. A 15N-recovery experiment was conducted in 13 diverse tropical agroecosystems. The objectives were to determine the total recovery of one single 15N application of inorganic or organic N during three to six growing seasons and to establish whether the losses of N are governed by universal principles. Between 7 and 58% (average of 21%) of crop N uptake duringthe first growing season was derived from fertilizer. On average, 79% of crop N was derived from the soil. When 15N-labeled residues were applied, in the first growing season 4% of crop N was derived from the residues. Average recoveries of 15N- labeled fertilizer and residue in crops after the first growing season were 33 and 7%, respectively. Corresponding recoveries in the soil were 38 and 71 %. An additional 6% of the fertilizer and 9.1 % of the residue was recovered by crops during subsequent growing seasons. There were no significant differences in total 15N recovery (average 54%) between N from fertilizer and N from residue. After five growing seasons, more residue N (40%) than fertilizer N (18%) was recovered in the soil, better sustaining the soil organic matter N content. Long-term total recoveries of 15N-labeled fertilizer or residue in the crop and soil were similar. Soil N remained the primary source of N for crops. As higher rainfall and temperature tend to cause higher N losses, management practices to improve N use efficiency and reduce losses in wet tropical regions will remain a challenge

Indicadores de calidad de la materia orgánica del suelo en un andisol cultivado

El manejo agronómico influye en la dinámica de la materia orgánica del suelo (MOS) y sus diferentes fracciones. En este estudio se determinaron fracciones activas de la MOS: fracción liviana libre (FLL), fracción liviana intraagregados (FLI), biomasa microbiana y C-CO2 mineralizado, en un suelo volcánico cultivado con distintas rotaciones, y posteriormente se evaluó su uso como indicadores biológicos del impacto del manejo agronómico en el suelo. El estudio se realizó en un experimento de campo de ocho años, con diferentes sistemas productivos (rotaciones) en un diseño de bloques completos al azar. La FLL fue determinada por fraccionamiento físico, usando NaI (1,8 g cm-3) y la FLI fue obtenida por sonicación (1.500 J s-1). La biomasa microbiana se cuantificó a través de fumigación-incubación (FI), y la respiración basal del suelo (evolución de C-CO2) por incubación durante 10 días. La rotación disminuyó (P £ 0,05) los contenidos de C y N de la FLL, de 1,69 g C-FLL kg-1 suelo (rotación con 5 años de alfalfa, Medicago sativa L.) a 0,49 g C-FLL kg-1 de suelo (rotación con cultivos anuales). Sin embargo, estos contenidos en la FLI no mostraron una tendencia clara y consistente (P £ 0,05). La biomasa C y N, disminuyeron (P £ 0,05) con la mayor intensidad de uso del suelo, de 551 a 264 µg C-CO2 g suelo-1, y de 106 a 35 µg N-(NO3- + NH4+) g suelo-1, respectivamente. Los tres índices estudiados representaron indicadores apropiados para determinar cambios en la calidad de la MOS producto del manejo agronómico

INVESTIGACIÓN - INDICADORES DE CALIDAD DE LA MATERIA ORGÁNICA DEL SUELO EN UN ANDISOL CULTIVADO (Soil organic matter quality indicators in a cultivated Andisol)

Agricultural practices influence the dynamics of soil organic matter (MOS) and its fractions. In this study, the following labile fractions of soil organic matter were determined: free light fraction (FLL), intra-aggregate light fraction (FLI), microbial biomass and mineralized C-CO2, on volcanic soil with different rotations, and later their use was evaluated as biological indicators of the impact of agricultural practices on the soil. The study was carried out in an eight year field experiment, with different productive systems (rotations) in a randomized complete block design. The free light fraction (FLL) was determined by density fractionation with NaI (1.8 g cm-3), and the intra-aggregate light fraction (FLI) was obtained by sonication (1,500 J s-1). Microbial biomass was quantified using the chloroform fumigation-incubation (FI) technique, and the basal soil respiration (C-CO2 evolution) was determined by incubation for a 10-day period. Increased soil use intensity decreased (P ≤ 0.05) C and N FLL contents, from 1.69 g C-FLL kg-1 soil (5-year rotation with alfalfa, Medicago sativa L.), to 0.49 g C-FLL kg-1 (annual crop rotation). However, these contents in FLI did not show a clear and consistent tendency (P ≤ 0.05). Soil biomass C and N decreased (P ≤ 0.05) with higher soil use intensity, from 551 to 264 μg C-CO2 g soil-1 and from 106 to 35 μg N-(NO3- + NH4+) g soil-1, respectively. The three studied indices were appropriate indicators to determine changes in soil organic matter quality as a result of agricultural practices

Variation of Greenhouse Gases Fluxes and Soil Properties with Addition of Biochar from Farm-Wastes in Volcanic and Non-Volcanic Soils

The decomposition of organic wastes contributes to greenhouse gas (GHG) emissions and global warming. This study evaluated the effect of biochar (BC) produced from different farm wastes (chicken, pig and cow manures) on greenhouse gas emissions and soil chemical and biological properties in different grassland soils (volcanic and non-volcanic soils). A 288-day laboratory experiment was carried out, monitoring CO2, N2O and CH4 emissions and evaluating total C, soil pH, microbial biomass and enzymatic activity in three grassland soils. The results varied depending on the soil type and feedstock of BC produced. BC-cow decreased emissions of CO2 and CH4 fluxes for volcanic and non-volcanic soils, probably due to decreases in β-glucosidase activity. Biochars from cow and pig manures increased soil C content, favouring the persistence of C into the soil at 288-days of incubation. Soil pH increased with the application of BC in the soils