Variability of soil fertility properties in areas planted to sugarcane in the State of Goias, Brazil

Soil sampling should provide an accurate representation of a given area so that recommendations for amendments of soil acidity, fertilization and soil conservation may be drafted to increase yield and improve the use of inputs. The aim of this study was to evaluate the variability of soil fertility properties of Oxisols in areas planted to sugarcane in the State of Goias, Brazil. Two areas of approximately 8,100 m² each were selected, representing two fields of the Goiasa sugarcane mill in Goiatuba. The sugarcane crop had a row spacing of 1.5 m and subsamples were taken from 49 points in the row and 49 between the row with a Dutch auger at depths of 0.0-0.2 and 0.2-0.4 m, for a total of 196 subsamples for each area. The samples were individually subjected to chemical analyses of soil fertility (pH in CaCl2, potential acidity, organic matter, P, K, Ca and Mg) and particle size analysis. The number of subsamples required to compose a sample within the acceptable ranges of error of 5, 10, 20 and 40 % of each property were computed from the coefficients of variation and the Student t-value for 95 % confidence. The soil properties under analysis exhibited different variabilities: high (P and K), medium (potential acidity, Ca and Mg) and low (pH, organic matter and clay content). Most of the properties analyzed showed an error of less than 20 % for a group of 20 subsamples, except for P and K, which were capable of showing an error greater than 40 % around the mean. The extreme variability in phosphorus, particularly at the depth of 0.2-0.4 m, attributed to banded application of high rates of P fertilizers at planting, places limitations on assessment of its availability due to the high number of subsamples required for a composite sample.

Available content, surface runoff and leaching of phosphorus forms in a typic hapludalf treated with organic and mineral nutrient sources

The application of animal manure to soil can increase phosphorus availability to plants and enhance transfer of the nutrient solution drained from the soil surface or leached into the soil profile. The aim of this study was to evaluate the effect of successive applications of organic and mineral nutrient sources on the available content, surface runoff and leaching of P forms in a Typic Hapludalf in no-tillage systems. Experiment 1 was set up in 2004 in the experimental area of UFSM, in Santa Maria (RS, Brazil). The treatments consisted of: control (without nutrient application) and application of pig slurry (PS), pig deep-litter (PL), cattle slurry (CS), and mineral fertilizers (NPK). The rates were determined to meet the N crop requirements of no-tillage black oat and maize, grown in the 2010/2011 growing season. The soil solution was collected after each event (rain + runoff or leaching) and the soluble, particulate and total P contents were measured. In November 2008, soil was collected in 2 cm intervals to a depth of 20 cm, in 5 cm intervals to a depth of 40 cm, and in 10 cm intervals to a depth of 70 cm. The soil was dried and ground, and P determined after extraction by anion exchange resin (AER). In experiment 2, samples collected from the Typic Hapludalf near experiment 1 were incubated for 20, 35, 58, 73 and 123 days after applying the following treatments: soil, soil + PS, soil + PL, soil + CS and soil + NPK. Thereafter, the soil was sampled and P was analyzed by AER. The applications of nutrient sources over the years led to an increase in available P and its migration in the soil profile. This led to P transfer via surface runoff and leaching, with the largest transfer being observed in PS and PL treatments, in which most P was applied. The soil available P and P transfer via surface runoff were correlated with the amounts applied, regardless of the P source. However, P transfer by leaching was not correlated with the applied nutrient amount, but rather with the solution amount leached in the soil profile.

Soil uses during the sugarcane fallow period: influence on soil chemical and physical properties and on sugarcane productivity

The planting of diversified crops during the sugarcane fallow period can improve the chemical and physical properties and increase the production potential of the soil for the next sugarcane cycle. The primary purpose of this study was to assess the influence of various soil uses during the sugarcane fallow period on soil chemical and physical properties and productivity after the first sugarcane harvest. The experiment was conducted in two areas located in Jaboticabal, São Paulo State, Brazil (21º 14' 05'' S, 48º 17' 09'' W) with two different soil types, namely: an eutroferric Red Latosol (RLe) with high-clay texture (clay content = 680 g kg-1) and an acric Red Latosol (RLa) with clayey texture (clay content = 440 g kg-1). A randomized block design with five replications and four treatments (crop sequences) was used. The crop sequences during the sugarcane fallow period were soybean/millet/soybean, soybean/sunn hemp/soybean, soybean/fallow/soybean, and soybean. Soil use was found not to affect chemical properties and sugarcane productivity of RLe or RLa. The soybean/millet/soybean sequence improved aggregation in the acric Latosol.

Comparison of digestion methods to determine heavy metals in fertilizers

The lack of a standard method to regulate heavy metal determination in Brazilian fertilizers and the subsequent use of several digestion methods have produced variations in the results, hampering interpretation. Thus, the aim of this study was to compare the effectiveness of three digestion methods for determination of metals such as Cd, Ni, Pb, and Cr in fertilizers. Samples of 45 fertilizers marketed in northeastern Brazil were used. A fertilizer sample with heavy metal contents certified by the US National Institute of Standards and Technology (NIST) was used as control. The following fertilizers were tested: rock phosphate; organo-mineral fertilizer with rock phosphate; single superphosphate; triple superphosphate; mixed N-P-K fertilizer; and fertilizer with micronutrients. The substances were digested according to the method recommended by the Ministry for Agriculture, Livestock and Supply of Brazil (MAPA) and by the two methods 3051A and 3052 of the United States Environmental Protection Agency (USEPA). By the USEPA method 3052, higher portions of the less soluble metals such as Ni and Pb were recovered, indicating that the conventional digestion methods for fertilizers underestimate the total amount of these elements. The results of the USEPA method 3051A were very similar to those of the method currently used in Brazil (Brasil, 2006). The latter is preferable, in view of the lower cost requirement for acids, a shorter digestion period and greater reproducibility.

Evaluation of statistical and geostatistical models of digital soil properties mapping in tropical mountain regions

Soil properties have an enormous impact on economic and environmental aspects of agricultural production. Quantitative relationships between soil properties and the factors that influence their variability are the basis of digital soil mapping. The predictive models of soil properties evaluated in this work are statistical (multiple linear regression-MLR) and geostatistical (ordinary kriging and co-kriging). The study was conducted in the municipality of Bom Jardim, RJ, using a soil database with 208 sampling points. Predictive models were evaluated for sand, silt and clay fractions, pH in water and organic carbon at six depths according to the specifications of the consortium of digital soil mapping at the global level (GlobalSoilMap). Continuous covariates and categorical predictors were used and their contributions to the model assessed. Only the environmental covariates elevation, aspect, stream power index (SPI), soil wetness index (SWI), normalized difference vegetation index (NDVI), and b3/b2 band ratio were significantly correlated with soil properties. The predictive models had a mean coefficient of determination of 0.21. Best results were obtained with the geostatistical predictive models, where the highest coefficient of determination 0.43 was associated with sand properties between 60 to 100 cm deep. The use of a sparse data set of soil properties for digital mapping can explain only part of the spatial variation of these properties. The results may be related to the sampling density and the quantity and quality of the environmental covariates and predictive models used.

Assessment of pedotransfer functions for estimating soil water retention curves for the amazon region

Knowledge of the soil water retention curve (SWRC) is essential for understanding and modeling hydraulic processes in the soil. However, direct determination of the SWRC is time consuming and costly. In addition, it requires a large number of samples, due to the high spatial and temporal variability of soil hydraulic properties. An alternative is the use of models, called pedotransfer functions (PTFs), which estimate the SWRC from easy-to-measure properties. The aim of this paper was to test the accuracy of 16 point or parametric PTFs reported in the literature on different soils from the south and southeast of the State of Pará, Brazil. The PTFs tested were proposed by Pidgeon (1972), Lal (1979), Aina & Periaswamy (1985), Arruda et al. (1987), Dijkerman (1988), Vereecken et al. (1989), Batjes (1996), van den Berg et al. (1997), Tomasella et al. (2000), Hodnett & Tomasella (2002), Oliveira et al. (2002), and Barros (2010). We used a database that includes soil texture (sand, silt, and clay), bulk density, soil organic carbon, soil pH, cation exchange capacity, and the SWRC. Most of the PTFs tested did not show good performance in estimating the SWRC. The parametric PTFs, however, performed better than the point PTFs in assessing the SWRC in the tested region. Among the parametric PTFs, those proposed by Tomasella et al. (2000) achieved the best accuracy in estimating the empirical parameters of the van Genuchten (1980) model, especially when tested in the top soil layer.

Compared performance of penetrometers and effect of soil water content on penetration resistance measurements

Modern agriculture techniques have a great impact on crops and soil quality, especially by the increased machinery traffic and weight. Several devices have been developed for determining soil properties in the field, aimed at managing compacted areas. Penetrometry is a widely used technique; however, there are several types of penetrometers, which have different action modes that can affect the soil resistance measurement. The objective of this study was to compare the functionality of two penetrometry methods (manual and automated mode) in the field identification of compacted, highly mechanized sugarcane areas, considering the influence of soil water volumetric content (θ) on soil penetration resistance (PR). Three sugarcane fields on a Rhodic Eutrudrox were chosen, under a sequence of harvest systems: one manual harvest (1ManH), one mechanized harvest (1MH) and three mechanized harvests (3MH). The different degrees of mechanization were associated to cumulative compaction processes. An electronic penetrometer was used on PR measurements, so that the rod was introduced into the soil by hand (Manual) and by an electromechanical motor (Auto). The θ was measured in the field with a soil moisture sensor. Results showed an effect of θ on PR measurements and that regression models must be used to correct data before comparing harvesting systems. The rod introduction modes resulted in different mean PR values, where the "Manual" overestimated PR compared to the "Auto" mode at low θ.

Multivariate analysis applied to the study of the relationship between soil and plant properties in a peach orchard

In the State of Rio Grande do Sul, the municipality of Pelotas is responsible for 90 % of peach production due to its suitable climate and soil conditions. However, there is the need for new studies that aim at improved fruit quality and increased yield. The aim of this study was to evaluate the relationship that exists between soil physical properties and properties in the peach plant in the years 2010 and 2011 by the technique of multivariate canonical correlation. The experiment was conducted in a peach orchard located in the municipality of Morro Redondo, RS, Brazil, where an experimental grid of 101 plants was established. In a trench dug beside each one of the 101 plants, soil samples were collected to determine silt, clay, and sand contents, soil density, total porosity, macroporosity, microporosity, and volumetric water content in the 0.00-0.10 and 0.10-0.20 m layers, as well as the depth of the A horizon. In each plant and in each year, the following properties were assessed: trunk diameter, fruit size and number of fruits per plant, average weight of the fruit per plant, fruit pulp firmness, Brix content, and yield from the orchard. Exploratory analysis of the data was undertaken by descriptive statistics, and the relationships between the physical properties of the soil and of the plant were assessed by canonical correlation analysis. The results showed that the clay and microporosity variables were those that exhibited the highest coefficients of canonical cross-loading with the plant properties in the soil layers assessed, and that the variable of mean weight of the fruit per plant was that which had the highest coefficients of canonical loading within the plant group for the two years assessed.

Congo grass grown in rotation with soybean affects phosphorus bound to soil carbon

The phosphorus supply to crops in tropical soils is deficient due to its somewhat insoluble nature in soil, and addition of P fertilizers has been necessary to achieve high yields. The objective of this study was to examine the mechanisms through which a cover crop (Congo grass - Brachiaria ruziziensis) in rotation with soybean can enhance soil and fertilizer P availability using long-term field trials and laboratory chemical fractionation approaches. The experimental field had been cropped to soybean in rotation with several species under no-till for six years. An application rate of no P or 240 kg ha-1 of P2O5 had been applied as triple superphosphate or as Arad rock phosphate. In April 2009, once more 0.0 or 80.0 kg ha-1 of P2O5 was applied to the same plots when Congo grass was planted. In November 2009, after Congo grass desiccation, soil samples were taken from the 0-5 and 5-10 cm depth layer and soil P was fractionated. Soil-available P increased to the depth of 10 cm through growing Congo grass when P fertilizers were applied. The C:P ratio was also increased by the cover crop. Congo grass cultivation increased P content in the soil humic fraction to the depth of 10 cm. Congo grass increases soil P availability by preventing fertilizer from being adsorbed and by increasing soil organic P.

Macronutrient uptake, accumulation and export by the irrigated 'vitória' pineapple plant

The nutritional state of the pineapple plant has a large effect on plant growth, on fruit production, and fruit quality. The aim of this study was to assess the uptake, accumulation, and export of nutrients by the irrigated 'Vitória' pineapple plant during and at the end of its development. A randomized block statistical design with four replications was used. The treatments were defined by different times of plant collection: at 270, 330, 390, 450, 510, 570, 690, 750, and 810 days after planting (DAP). The collected plants were separated into the following components: leaves, stem, roots, fruit, and slips for determination of fresh and dry matter weight at 65 ºC. After drying, the plant components were ground for characterization of the composition and content of nutrients taken up and exported by the pineapple plant. The results were subjected to analysis of variance, and non-linear regression models were fitted for the significant differences identified by the F test (p<0.01). The leaves and the stem were the plant components that showed the greatest accumulation of nutrients. For production of 72 t ha-1 of fruit, the macronutrient accumulation in the 'Vitória' pineapple exhibited the following decreasing order: K > N > S > Ca > Mg > P, which corresponded to 898, 452, 134, 129, 126, and 107 kg ha-1, respectively, of total accumulation. The export of macronutrients by the pineapple fruit was in the following decreasing order: K > N > S > Ca > P > Mg, which was equivalent to 18, 17, 11, 8, 8, and 5 %, respectively, of the total accumulated by the pineapple. The 'Vitória' pineapple plant exported 78 kg ha-1 of N, 8 kg ha-1 of P, 164 kg ha-1 of K, 14 kg ha-1 of S, 10 kg ha-1 of Ca, and 6 kg ha-1 of Mg by the fruit. The nutrient content exported by the fruits represent important components of nutrient extraction from the soil, which need to be restored, while the nutrients contained in the leaves, stems and roots can be incorporated in the soil within a program of recycling of crop residues.

Effect of management systems and cover crops on organic matter dynamics of soil under vegetables

Vegetable production in conservation tillage has increased in Brazil, with positive effects on the soil quality. Since management systems alter the quantity and quality of organic matter, this study evaluated the influence of different management systems and cover crops on the organic matter dynamics of a dystrophic Red Latosol under vegetables. The treatments consisted of the combination of three soil tillage systems: no-tillage (NT), reduced tillage (RT) and conventional tillage (CT) and of two cover crops: maize monoculture and maize-mucuna intercrop. Vegetables were grown in the winter and the cover crops in the summer for straw production. The experiment was arranged in a randomized block design with four replications. Soil samples were collected between the crop rows in three layers (0.0-0.05, 0.05-0.10, and 0.10-0.30 m) twice: in October, before planting cover crops for straw, and in July, during vegetable cultivation. The total organic carbon (TOC), microbial biomass carbon (MBC), oxidizable fractions, and the carbon fractions fulvic acid (C FA), humic acid (C HA) and humin (C HUM) were determined. The main changes in these properties occurred in the upper layers (0.0-0.05 and 0.05-0.10 m) where, in general, TOC levels were highest in NT with maize straw. The MBC levels were lowest in CT systems, indicating sensitivity to soil disturbance. Under mucuna, the levels of C HA were lower in RT than NT systems, while the C FA levels were lower in RT than CT. For vegetable production, the C HUM values were lowest in the 0.05-0.10 m layer under CT. With regard to the oxidizable fractions, the tillage systems differed only in the most labile C fractions, with higher levels in NT than CT in the 0.0-0.05 m layer in both summer and winter, with no differences between these systems in the other layers. The cabbage yield was not influenced by the soil management system, but benefited from the mulch production of the preceding maize-mucuna intercrop as cover plant.

Rice husk ash as corrective of soil acidity

Rice husk ash (RHA) is a by-product from the burning of rice husk that can have favorable effects on the soil in terms of acidity correction. The objectives of this study were to determine the effective calcium carbonate equivalent (ECC) of RHA under field conditions, and establish technical criteria as a basis for estimating the overall ECC of RHA. The 12 treatments of the experiment consisted of 10 RHA dosages (0, 10, 20, 30, 40, 60, 80, 100, 120, and 140 Mg ha-1) and two references, one of which was an absolute control (AC) and the other a plot limed and fertilized according to official recommendations (recommended fertilization - RF). The soil was sampled twice (15 and 210 days after incorporating RHA), in the layers 0.00-0.10 and 0.10-0.20 m, to determine the pH(H2O) and base saturation (V%). The ECC and neutralizing value (NV) of RHA were also determined. The results showed that RHA neutralizes soil acidity, in a faster reaction than conventional limestone, despite a low ECC (around 3 %).

Forms of phosphorus in an oxisol under different soil tillage systems and cover plants in rotation with maize

Phosphorus fractions play a key role in sustaining the productivity of acid-savanna Oxisols and are influenced by tillage practices. The aim of this study was to quantify different P forms in an Oxisol (Latossolo Vermelho-Amarelo) from the central savanna region of Brazil under management systems with cover crops in maize rotation. Three cover crops (Canavalia brasiliensis, Cajanus cajan (L.), and Raphanus sativus L.) were investigated in maize rotation systems. These cover crops were compared to spontaneous vegetation. The inorganic forms NaHCO3-iP and NaOH-iP represented more than half of the total P in the samples collected at the depth of 5-10 cm during the rainy season when the maize was grown. The concentration of inorganic P of greater availability (NaHCO3-iP and NaOH-iP) was higher in the soil under no-tillage at the depth of 5-10 cm during the rainy season. Concentrations of organic P were higher during the dry season, when the cover crops were grown. At the dry season, organic P constituted 70 % of the labile P in the soil planted to C. cajan under no-tillage. The cover crops were able to maintain larger fractions of P available to the maize, resulting in reduced P losses to the unavailable pools, mainly in no-tillage systems.

Three-dimensional interpolation of soil data: fertility and pedomorphological features in southern Brazil

The graphical representation of spatial soil properties in a digital environment is complex because it requires a conversion of data collected in a discrete form onto a continuous surface. The objective of this study was to apply three-dimension techniques of interpolation and visualization on soil texture and fertility properties and establish relationships with pedogenetic factors and processes in a slope area. The GRASS Geographic Information System was used to generate three-dimensional models and ParaView software to visualize soil volumes. Samples of the A, AB, BA, and B horizons were collected in a regular 122-point grid in an area of 13 ha, in Pinhais, PR, in southern Brazil. Geoprocessing and graphic computing techniques were effective in identifying and delimiting soil volumes of distinct ranges of fertility properties confined within the soil matrix. Both three-dimensional interpolation and the visualization tool facilitated interpretation in a continuous space (volumes) of the cause-effect relationships between soil texture and fertility properties and pedological factors and processes, such as higher clay contents following the drainage lines of the area. The flattest part with more weathered soils (Oxisols) had the highest pH values and lower Al3+ concentrations. These techniques of data interpolation and visualization have great potential for use in diverse areas of soil science, such as identification of soil volumes occurring side-by-side but that exhibit different physical, chemical, and mineralogical conditions for plant root growth, and monitoring of plumes of organic and inorganic pollutants in soils and sediments, among other applications. The methodological details for interpolation and a three-dimensional view of soil data are presented here.

Phosphorus availability in oxidic soils treated with lime and silicate applications

Based on the assumption that silicate application can raise soil P availability for crops, the aim of this research was to compare the effect of silicate application on soil P desorption with that of liming, in evaluations based on two extractors and plant growth. The experiment was carried out in randomized blocks with four replications, in a 3 × 3 × 5 factorial design, in which three soil types, three P rates, and four soil acidity correctives were evaluated in 180 experimental plots. Trials were performed in a greenhouse using corn plants in 20-dm³ pots. Three P rates (0, 50 and 150 mg dm-3) were applied in the form of powder triple superphosphate and the soil was incubated for 90 days. After this period, soil samples were collected for routine chemical analysis and P content determination by the extraction methods resin, Mehlich-1 and remaining P. Based on the results, acidity correctives were applied at rates calculated for base saturation increased to 70 %, with subsequent incubation for 60 more days, when P content was determined again. The acidity correctives consisted of: dolomitic lime, steelmaking slag, ladle furnace slag, and wollastonite. Therefore, our results showed that slags raised the soil P content more than lime, suggesting a positive correlation between P and Si in soil. Silicon did not affect the extractor choice since both Mehlich-1 and resin had the same behavior regarding extracted P when silicon was applied to the soil. For all evaluated plant parameters, there was significant interaction between P rates and correctives; highest values were obtained with silicate.