Savanna Oxisol Research Articles

Land use change and its effect on ecosystem services in an Oxisol of the eastern High Plains of meta department in Colombia

Increasing cultivation on acid soils of Colombia’s Eastern High Plains in the Orinoquia region require crop management strategies that balance commercial and environmental interests. Previous research showed the effects of land preparation and management on certain aspects of ecosystem services of these acid soils. This research aimed to comprehensively evaluate the impact of use and soil management in a native savanna Oxisol converted to five production systems gaining traction among local farmers: Annual crops rotation–sugarcane (ACR-S); Annual crops rotation-maize-soybean (ACR-MS); Sugarcane monocrop (SM); Rubber associated with Desmodium ovalifollium (R-Do) as a cover crop; Pasture Brachiaria decumbens - Annual crops rotation (PBd-ACR) and native savanna (NS) as a control. The experimental design consisted of conditioning the soil with two doses of dolomitic lime and incorporating three tillage methods over 5 years. A Principal Components Analysis (PCA) constructed indicators of ecosystem services (ES), such as fertility, water regulation, macroinvertebrate diversity, climate control related to greenhouse gas emissions (GHG) and carbon stock. The indicator values were adjusted between 0.10 and 1.0. Physicochemical variables with the greatest statistical weight were identified for components 1 and 2 each year. The fertility indicator of the native savanna for year one had a low range with a value of 0.11 compared to the other systems (p ≤ 0.05). During the years two, three, and four, soil fertility increased in the PBd-ACR (0.51) production system compared to the other systems. PBd-ACR generally improved water supply, although with lower indicator values than ACR-MS and R-Do. PBd-ACR show high biodiversity for edaphic macroinvertebrates compared to other systems. Field measurements detected methane emissions only in the SM system. Oxisols changed with the introduction of crops. The positive and negative tradeoffs of production systems and their agronomic practices should be considered in agricultural development of these acid soils.

Exchangeable potassium reserve in a Brazilian savanna Oxisol after nine years under different cotton production systems

Adequate potassium (K) fertilization is essential for agricultural production in soils of the Brazilian Savanna (Cerrado biome) due to the high demand by crops (especially cotton), likelihood of leaching losses, and the dependence on fertilizer importations. Therefore, sustainability requires improvements in the soil efficiency management. This study evaluated the influence of soil management and crop succession or rotation combinations with cotton on K dynamics and exchangeable reserves in the soil profile, and the partial balance of K after nine years of cultivation in a clayey Oxisol in the Cerrado. The soil was sampled in layers up to 100 cm depth in four cotton production systems treatments: 1) conventional soil tillage (CST) with cotton monoculture; 2) CST with annual cotton-soybean-cotton succession; 3) CST with cotton/soybean/maize rotation; and 4) no-tillage system (NTS) with cotton/soybean/maize rotation and Urochloa ruziziensis (ruzigrass) as a cover crop in the off-season after grain crops. The experiment was conducted using a randomized block design with four replications. CST with cotton monoculture favored the leaching of K surplus from fertilization. Crop rotation including ruzigrass in the NTS allowed better control of K dynamics, ensuring its circulation in the soil-plant compartments and reducing leaching. The increased organic matter (OM) in this system enlarges the storage capacity of K in the topsoil. The adoption of no-tillage crop systems integrating ruzigrass is viable to improve the efficiency of K fertilizers in cotton cultivation in highly weathered tropical soils.

Nutrient Leaching in a Colombian Savanna Oxisol Amended with Biochar

Nutrient leaching in highly weathered tropical soils often poses a challenge for crop production. We investigated the effects of applying 20 t ha biochar (BC) to a Colombian savanna Oxisol on soil hydrology and nutrient leaching in field experiments. Measurements were made over the third and fourth years after a single BC application. Nutrient contents in the soil solution were measured under one maize and one soybean crop each year that were routinely fertilized with mineral fertilizers. Leaching by unsaturated water flux was calculated using soil solution sampled with suction cup lysimeters and water flux estimates generated by the model HYDRUS 1-D. No significant difference ( > 0.05) was observed in surface-saturated hydraulic conductivity or soil water retention curves, resulting in no relevant changes in water percolation after BC additions in the studied soils. However, due to differences in soil solution concentrations, leaching of inorganic N, Ca, Mg, and K measured up to a depth of 0.6 m increased ( < 0.05), whereas P leaching decreased, and leaching of all nutrients (except P) at a depth of 1.2 m was significantly reduced with BC application. Changes in leaching at 2.0 m depth with BC additions were about one order of magnitude lower than at other depths, except for P. Biochar applications increased soil solution concentrations and downward movement of nutrients in the root zone and decreased leaching of Ca, Mg, and Sr at 1.2 m, possibly by a combination of retention and crop nutrient uptake.

Maize yield and nutrition during 4 years after biochar application to a Colombian savanna oxisol

The application of biochar (biomass-derived black carbon) to soil has been shown to improve crop yields, but the reasons for this are often not clearly demonstrated. Here, we studied the effect of a single application of 0, 8 and 20 t ha−1 of biochar to a Colombian savanna Oxisol for 4 years (2003–2006), under a maize-soybean rotation. Soil sampling to 30 cm was carried out after maize harvest in all years but 2005, maize tissue samples were collected and crop biomass was measured at harvest. Maize grain yield did not significantly increase in the first year, but increases in the 20 t ha−1 plots over the control were 28, 30 and 140% for 2004, 2005 and 2006, respectively. The availability of nutrients such as Ca and Mg was greater with biochar, and crop tissue analyses showed that Ca and Mg were limiting in this system. Soil pH increased, and exchangeable acidity showed a decreasing trend with biochar application. We attribute the greater crop yield and nutrient uptake primarily to the 77–320% greater available Ca and Mg in soil where biochar was applied.

Fate of soil‐applied black carbon: downward migration, leaching and soil respiration

AbstractBlack carbon (BC) is an important pool of the global C cycle, because it cycles much more slowly than others and may even be managed for C sequestration. Using stable isotope techniques, we investigated the fate of BC applied to a savanna Oxisol in Colombia at rates of 0, 11.6, 23.2 and 116.1 t BC ha−1, as well as its effect on non‐BC soil organic C. During the rainy seasons of 2005 and 2006, soil respiration was measured using soda lime traps, particulate and dissolved organic C (POC and DOC) moving by saturated flow was sampled continuously at 0.15 and 0.3 m, and soil was sampled to 2.0 m. Black C was found below the application depth of 0–0.1 m in the 0.15–0.3 m depth interval, with migration rates of 52.4±14.5, 51.8±18.5 and 378.7±196.9 kg C ha−1 yr−1 (±SE) where 11.6, 23.2 and 116.1 t BC ha−1, respectively, had been applied. Over 2 years after application, 2.2% of BC applied at 23.2 t BC ha−1 was lost by respiration, and an even smaller fraction of 1% was mobilized by percolating water. Carbon from BC moved to a greater extent as DOC than POC. The largest flux of BC from the field (20–53% of applied BC) was not accounted for by our measurements and is assumed to have occurred by surface runoff during intense rain events. Black C caused a 189% increase in aboveground biomass production measured 5 months after application (2.4–4.5 t additional dry biomass ha−1 where BC was applied), and this resulted in greater amounts of non‐BC being respired, leached and found in soil for the duration of the experiment. These increases can be quantitatively explained by estimates of greater belowground net primary productivity with BC addition.

COMPONENTES BIÓTICOS DE UM CAMPO DE PESQUISA SOB QUATRO SISTEMAS DE MANEJO DE SOLO

Organic matter was studied in a savanna oxisol during two years, in Santa Helena, state of Goias, Brazil, a traditional no-till management area, in which four soil management systems were developed: no-tillage (PD), deep moldboard plowing (AP), shallow harrow plowing (GA) and deep stirring, using a chiseling plower (EP). The dry matter from weed plants observed in the area produced 2369, 124, 243, 640 kg/ha in PD, AP, GA and EP, about 30 days after soil management, respectively. The organic matter was concentrated in the arable soil layer in areas where no-till management was adopted (PD) and was dispersed in larger depth in areas where deep plowing (AP) was used. Deep stirring (EP) behaved similarly to the no-till management (PD). Lower pH values were verified at arable surface under the no-till management. Larger number of fungi and bacteria, as well as of propagules of Rhizoctonia solani and Fusarium solani , were also observed in the no-tillage areas (PD). KEY-WORDS: Organic matter; soil pathogenic agents; no-till management.

Tillage effects on maize yield in a Colombian savanna oxisol: Soil organic matter and P fractions

Soil organic matter (SOM) and phosphorus (P) fractions play a key role in sustaining the productivity of acid-savanna oxisols and are greatly influenced by tillage practices. In 1993, a long-term experiment on sustainable crop rotation and ley farming systems was initiated on a Colombian acid-savanna oxisol to test the effects of grain legumes, green manures, intercrops and leys as possible components that could increase the stability of systems involving annual cereal crops. Five agropastoral treatments (maize monoculture—MMO, maize–soybean rotation—MRT, maize–soybean green manure rotation—MGM, native savanna control—NSC and maize-agropastoral rotation—MAP) under two tillage systems (no till-NT and minimum tillage-MT) were investigated. The effects of NT and MT on SOM and P fractions as well as maize grain yield under the five agropastoral treatments were evaluated. Results showed that soil total C, N and P were generally better under no-till as compared to minimum-tilled soils. While P fractions were also generally higher under no-till treatments, SOM fractions did not show any specific trend. Seven years after establishment of the long-term ley farming experiment (5 years of conventional tillage followed by 2 years alternative tillage systems), MT resulted into moderately higher maize grain yields as compared to NT. The MGM rotation treatment had significantly higher values of maize yield under both tillage systems (4.2 Mg) compared to the NSC (2.3 Mg ha −1). Results from this study indicate that the rotational systems (maize–soybean green manure and maize-pastures) improved the soil conditions to implement the no-till or minimum tillage systems on Colombian savanna oxisol.

Nutrient Leaching in Oxisols Under Native and Managed Vegetation in Brazil

Brazilian savanna Oxisols are prone to nutrient leaching because of low nutrient retention and high water conductivity. We determined downward and upward fluxes of Ca, Mg, K, NH4–N, and NO3–N at 0.3‐, 0.8‐, and 2.0‐m soil depths under native savanna vegetation (Cerrado), Pinus caribaea Morelet plantation, managed productive Brachiaria decumbens Stapf pasture, degraded B. decumbens pasture, conventional tillage, and no‐till corn (Zea mays L.)–soybean [Glycine max (L.) Merr.] cropping using exchange resin cores, and set up a nutrient budget using previously published input data. At each of the study depths, we installed three to six PVC tubes (0.10 m in diameter, 0.11 m in length) filled with a mixture of field‐fresh soil and HBr‐washed ion exchange resin (Amberlite MB‐20, 10:1 v/v), which were removed and extracted after 2 yr. Downward fluxes at 2‐m soil depth ranged from 0.22 to 2.3 g Ca, 0.02 to 0.71 g Mg, 0.08 to 1.17 g K, not detected (n.d.) to 0.96 g NH4–N, and n.d. to 4.4 g NO3–N m−2 yr−1 Upward fluxes, because of capillary rise, frequently amounted to 30 to 50% of downward fluxes. At 0.3‐m depth, net leaching fluxes of Ca in the cropping systems and productive pasture (2.3–4.9 g m−2 yr−1) and of K and NO3–N in the cropping systems (K: 0.73–0.85, NO3–N: 2.3) were significantly higher than in all other systems except for NO3–N in Pinus (Ca: 0.02–0.18, K: 0.09–0.15; NO3–N: n.d.–0.70). In forests and pastures, all nutrients accumulated on balance while in cropping systems budgets were balanced or negative except for N. To reduce these losses, timing of fertilizer amendments should be optimized and in the no‐till system evaporation and fast water fluxes reduced for example, by stubble mulching.

Subsoil retention of organic and inorganic nitrogen in a Brazilian savanna Oxisol

Abstract. Nitrogen (N) loss by leaching poses great challenges for N availability to crops as well as nitrate pollution of groundwater. Few studies address this issue with respect to the role of the subsoil in the deep and highly weathered savanna soils of the tropics, which exhibit different adsorption and drainage patterns to soils in temperate environments. In an Anionic Acrustox of the Brazilian savanna, the Cerrado, dynamics and budgets of applied N were studied in organic and inorganic soil pools of two maize (Zea mays L.) – soybean (Glycine max (L.) Merr.) rotations using 15N tracing. Labelled ammonium sulphate was applied at 10 kg N ha−1 (with 10 atom%15N excess) to both maize and soybean at the beginning of the cropping season. Amounts and isotopic composition of N were determined in above‐ground biomass, soil, adsorbed mineral N, and in soil solution at 0.15, 0.3, 0.8, 1.2 and 2 m depths using suction lysimeters throughout one cropping season. The applied ammonium was rapidly nitrified or immobilized in soil organic matter, and recovery of applied ammonium in soil 2 weeks after application was negligible. Large amounts of nitrate were adsorbed in the subsoil (150–300 kg NO3−‐N ha−1 per 2 m) matching total N uptake by the crops (130–400 kg N ha−1). Throughout one cropping season, more applied N (49–77%; determined by 15N tracers) was immobilized in soil organic matter than was present as adsorbed nitrate (2–3%). Most of the applied N (71–96% of 15N recovery) was found in the subsoil at 0.15–2 m depth. This coincided with an increase with depth of dissolved organic N as a proportion of total dissolved N (39–63%). Hydrophilic organic N was the dominant fraction of dissolved organic N and was, together with nitrate, the most important carrier for applied N. Most of this N (&gt;80%) was leached from the topsoil (0–0.15 m) during the first 30 days after application. Subsoil N retention as both adsorbed inorganic N, and especially soil organic N, was found to be of great importance in determining N losses, soil N depletion and the potential of nitrate contamination of groundwater.

Subsoil retention of organic and inorganic nitrogen in a Brazilian savanna Oxisol

Subsoil retention of organic and inorganic nitrogen in a Brazilian savanna Oxisol

Phosphorus fractions and dynamics in surface earthworm casts under native and improved grasslands in a Colombian savanna Oxisol

The objective of this study was to assess the effect of a native anecic species on phosphorus availability in an Oxisol characterised by a low chemical fertility. Experiments were carried out at Carimagua research station in a representative site of the isohyperthermic savannas on the Colombian Orinoco basin. One field study and two laboratory/incubation studies were performed in a natural herbaceous savanna and a Brachiaria decumbens and Pueraria phaseoloides pasture. In the laboratory, experiment pots were prepared containing soil collected from the respective field paddock's topsoil. Total P content was higher in earthworm casts than in the surrounding soil in field samples, 50% in native savanna soil and more than 100% in pasture soil. In casts produced under laboratory conditions this increase was relatively low (10–20%). Under field conditions, almost without exception, all P fractions were increased in casts relative to the original soil (corresponding to the increase in total P content), being relatively greater in the labile inorganic P fractions. In addition, samples from the natural savanna showed that pH of casts was higher (5.2) than that of soil (4.6) in both field and laboratory samples. Except in the native savanna under field conditions, the phosphatase activity was reduced in casts by 16.7 to 44%. From our results we conclude that earthworms in the field incorporate P from litter or other organic sources (i.e. undecomposed plant and root material, earthworm faeces) which is not normally measured in the analysis of bulk soil.

Effects of Pinus caribaea forests on the C, N, P, and S status of Brazilian savanna Oxisols

Abstract The accumulation of humus in soils under Pinus caribaea Morelet forests may increase the availability of organically bound N, P, and S to plants and thus improve soil fertility. To test this hypothesis, we compared C, N, P, and S concentrations and forms in soil solid phase and soil solution under Pinus (PI) and natural savanna vegetation ( Cerrado , CE). We sampled the 0–0.15, 0.15–0.3, 0.3–0.8, 0.8–1.2, and 1.2–2 m soil depth layers of Oxisols from three spatially separated plots under CE and PI; at each plot, soil solution at 0.15, 0.3, 0.8, 1.2, and 2 m soil depth and under PI additionally below the organic layer was collected during two rainy seasons (21 October–28 April 1997/1998 and 1998/1999). Under PI, the organic layer stored more C (24.5 t ha −1 ), N (2.6 t ha −1 ), P (140 kg ha −1 ), and S (261 kg ha −1 ) than under CE (1.2 t C ha −1 , 23 kg N ha −1 , 1.2 kg P ha −1 , 2.3 kg S ha −1 ). No significant difference in C, N, P, and S concentrations between CE and PI in the surface horizons of the mineral soil (C: 20.7–23.4 g kg −1 , N: 1.2–1.5 g kg −1 , P: 0.16–0.26 g kg −1 , S: 0.18–0.21 g kg −1 ) was observed. However, at 1.2–2 m soil depth C and organic N (N org ) concentrations were significantly higher under PI (C: 6.9 g kg −1 , N org : 0.54 g kg −1 ) than under CE (C: 6.4 g kg −1 , N org : 0.41 g kg −1 ). C/P and C/S ratios in soil solid phase decreased with increasing soil depth under CE and PI, those of C/N org only under PI, leading to narrower C/N org ratios under PI (12.9) than under CE (15.6) at 1.2–2 m soil depth. The result indicated enhanced N transport to the subsoil under PI. Total organic C concentrations (TOC) in the soil solution were similar under CE and PI and throughout the mineral soil. Under PI, TOC concentrations decreased sharply between the litter leachate (30 mg C l −1 ) and 0.15 m soil depth (5 mg C l −1 ) indicating strong TOC sorption onto the surface mineral soil. Total N concentrations in the soil solution were 11–23 times higher under PI than under CE. Organic N concentrations also decreased between the litter leachate and 0.15 m soil depth under PI but NO 3 − concentrations increased from the litter leachate to 1.2 m soil depth and decreased between 1.2 and 2 soil depth, probably due to enhanced anion sorption at 2 m soil depth. No S and P was detectable in any solution sample. Higher C, N, and S storages and higher N availability under PI indicated that PI forests improve C, N, P, and S supply for plants in subsequent cultures and may therefore be considered sustainable with respect to organically bound nutrients.

Effect of No-Tillage and Conventional Tillage Systems on the Chemical Composition of Soil Solid Phase and Soil Solution of Brazilian Savanna Oxisols

No-tillage (NT) cropping systems are becoming increasingly important in the Brazilian savanna. To evaluate their sustainability we compared soil chemical properties in 1- to 3-year-old NT systems following 9 to 11 years of conventional tillage (CT) with systems where CT was continuously in place for 12 years. In the rainy season 1997/98, NT was cropped with soybean and CT with corn while in the rainy season 1998/99 both systems were cropped with soybean. Soil solid phase samples were taken from the 0-0.15, 0.15-0.3, 0.3-0.8, 0.8-1.2, and 1.2-2 m layers on three spatially separated plots under each of NT and CT. Soil solution samples were collected weekly at 0.15, 0.3, 0.8, 1.2, and 2 m soil depth during two rainy seasons (14 October to 28 April 1997/98 and 1998/99). We determined soil moisture contents, pH, the concentrations of exchangeable cations, the electrical conductivity (EC) of the soil solution, and the concentrations of Al, C, Ca, Cl - , K, Mg, Mn, Na, NH 4 + , NO 3 - , P, S, and Zn in solid soil and soil solution samples. Differences in soil solid phase properties and moisture content between NT and CT were small, few were significant. Under NT, the average solution pH was significantly lower (5.5), Al (26 tag 1 -1 ), Mn (17 μg 1 -1 ) and total organic C concentrations (TOC, 6.5 mg 1 -1 ) were higher than under CT (pH: 6.0, Al: 14μg 1 -1 , Mn: 14μg 1 -1 , TOC: 5.5 mg 1 -1 ). Irrespective of the different crops in the first rainy season, under NT, the EC (205 μS cm -1 ), Ca (17 mg 1 -1 ), and Mg (2.9 mg 1 -1 ) concentrations at 0-0.3 m depth were lower than under CT (EC: 224 μS cm -1 , Ca: 25 mg 1 -1 , Mg: 5.6 mg 1 -1 ). At 1.2-2 m depth, the reverse order was observed (EC: 124 μS cm -1 under NT and 84 μS cm -1 under CT, Ca: 11 mg 1 -1 under NT and 7.5 mg 1 -1 under CT, Mg: 3.1 mg 1 -1 under NT and 1.8 mg 1 -1 under CT). Our results indicate that enhanced soil acidification because of higher rates of organic matter mineralization and a more pronounced nutrient leaching because of increased pore continuity may limit the sustainability of NT.

Soil acidification in Pinus caribaea forests on Brazilian savanna Oxisols

The transformation of large areas in the Brazilian savanna into Pinus plantations may have resulted in soil acidification. The objective of this study was to determine if afforestation with Pinus caribaea Morelet (PI) influenced soil acidification by comparing the metal status of the soil solid phase and the course of metal concentrations in soil solution during one rainy season with those under natural savanna vegetation ( Cerrado, CE). Surface soil samples (0–0.15 m) from three spatially disconnected plots in CE and PI were sequentially extracted. At each plot, soil solution at 0.15, 0.3, 0.8, 1.2, and 2 m depth and in PI additionally litter leachate were collected between October 1997 and April 1998. Extracts and soil solution were analyzed for Al, Ca, Cu, Fe, K, Mg, Mn, Na, Si, and Zn concentrations, soil solution also for pH and electrical conductivity (EC). Total concentrations in soil solid phase ranged between 94 000 and 155 000 mg kg −1 (Al), 29 and 39 (Ca), 21 and 31 (Cu), 44 000 and 61 000 (Fe), 91 and 141 (K), 21 and 29 (Mg), 28 and 57 (Mn), 73 and 94 (Na), and 13 and 21 (Zn). Whereas 27–83% of total K, Ca, Mg, and Na concentrations were exchangeable, >83% of total Cu, Fe, Mn, Zn, and Al were bound in hardly plant-available forms. There were no significant differences in concentrations and partitioning between CE and PI. At the beginning of the rainy season (October to December), metal concentrations in soil solution were 2–5 times larger and more variable than between December and April because of the mineralization of organic matter which accumulated during the dry season. Metal concentrations in CE soil solution between December and April were extremely small at all depths (Al: not detected (n.d.)–3.26 μmol l −1, Ca: 2.8–11.7, K: 0.9–6.7, Mg: 0.7–8.3, Mn: n.d. −0.14, Na: 5.5–40.1, Zn: 0.13–1.02). Up to 1.2 m soil depth, soil solution pH was significantly lower in PI than in CE. Concentrations of Ca, K, Mg, and Na were up to two times larger than in CE, those of Mn and Al 9 and 60 times, respectively. Whereas the soil solid phase did not show significant differences in metal concentrations and partitioning, the soil solution composition clearly indicated enhanced acidification in PI. This resulted in increased leaching of plant nutrients from the topsoil.

Annual Course of Matric Potential in Differently Used Savanna Oxisols in Brazil

Sustainable land use in periodically dry Brazilian savannas requires a water‐saving management. We hypothesized that the annual course of matric potentials (ψM) in very‐fine, isohyperthermic Anionic Acrustoxes of Pinus plantations (PI), degraded (DP) and productive pastures (PP), no‐till (NT) and conventional tillage (CT) cropping, and natural savanna (Cerrado, CE) differed significantly. On three plots in each of these land‐use systems water input and ψM at the 0.15‐, 0.30‐, 0.80‐, 1.2‐, and 2.0‐m depths was measured with tensiometers weekly between 27 Mar. 1997 and 28 Apr. 1998. Precipitation between 29 Apr. 1997 and 28 Apr. 1998 was 1562 mm, with only 210 mm in May to September, when ψM at the 0.15‐ and 0.30‐m depths decreased to less than −80 kPa in all systems; the lowest ψM at 2‐m depth was −57 kPa. During the monitored period, the PI soils had lower average ψM at the 0.8‐ to 2‐m depths (−60 kPa) than those in CE (−46), indicating higher rainfall interception losses and higher transpiration. In CT, average ψM values at the 0.8‐ to 2‐m depths (−29) were higher than in NT (−51) because of different crops and different soil management. Between June and November, ψM at the 2‐m depth in CE decreased to a lower value (−42) than in vegetation‐free CT (−22) and NT (−27). In DP and PP soils, ψMs were similar to those in CE soils at all depths. The estimated average water storage in the upper 2 m during the monitored period was: 565 mm (CT) &gt; 553 (PP) &gt; 541 (DP) &gt; 537 (CE) &gt; 526 (NT) &gt; 479 (PI). Our results show that mainly the vegetation type and tillage practices control the annual course of matric potential in differently used savanna Oxisols.

Nitrogen dynamics associated with earthworm casts of Martiodrilus carimaguensis Jiménez and Moreno in a Colombian savanna Oxisol

Nitrogen dynamics associated with earthworm casts of Martiodrilus carimaguensis Jiménez and Moreno in a Colombian savanna Oxisol