Search

Solute leaching below the crop-rooting zone represents not only a valuable loss of nutrients for the plant, but also a potential pollution source of groundwater. The objective of this work was to quantify nutrient-leaching losses at 0.9 m depth in an Ultisol that was cultivated with sugarcane, located in the county of Jaboticabal-SP, Brazil. The following ions were evaluated: nitrite, nitrate, ammonium, sulfate, phosphate, calcium, magnesium and potassium. The first ratoon cycle was monitored from November 16, 2006, to July 9, 2007. The experimental design was organized as four random blocks and three treatments: T 1 : without fertilizer; T 2 : 100 kg ha −1 of N and 114 kg ha −1 of S; and T 3 : 150 kg ha −1 of N and 172 kg ha −1 of S. To determine the fate of the N-fertilizer and S-fertilizer, four microplots were installed, in which 2.15% atoms of 15 N- and 10.5% atoms of 34 S-enriched ammonium sulfate were applied. The input and output of anions and cations were quantified from the flux density of water and the ion concentration. The NO 3 − , K + , Mg 2+ and Ca 2+ concentrations in the soil increased in January following both rainfall and drainage. The leaching of N was between 3.9 and 34.9 kg ha −1 . The N leached derived from the 100 kg ha −1 applied N fertilizer was 22.5 kg ha −1 . The S leached was between 4.6 and 8.4 kg ha −1 . From the 114 kg ha −1 S applied as fertilizer the leaching was 0.480 kg ha −1 . The maximum leaching of P, K, Ca, and Mg were 1.2, 53.6, 135.7 and 39.8 kg ha −1 , respectively. From the results, it is not possible to determine whether the local groundwater will be contaminated, but caution should be taken to maintain soil quality by reducing the leaching loss of nutrients. [ABSTRACT FROM AUTHOR]

Abstract: The objective of this study was to analyze the components of the water balance in an Ultisol, located in the municipality of Jaboticabal, SP, Brazil (21°20′20″S, 48°18′35″W), that was cultivated with sugarcane. The monitoring was performed during the agricultural cycle of the first ratoon between 11/16/2006 and 7/9/2007. Three treatments were established in four blocks with doses of ammonium sulfate, as follows: Treatment 1 (T1), without fertilizer; Treatment 2 (T2), 100kgha−1 of nitrogen (N) and 114kgha−1 of sulfur (S); and Treatment 3 (T3), 150kgha−1 of N and 172kgha−1 of S. Rainy precipitation (P) in the area was measured with a rain gauge. The soil water storage (H) and the soil water storage variations (ΔH) were determined by the gravimetric method, and the internal drainage (D)/capillary rise (CR) at a depth of 0.9m was quantified by the water flux density using the Darcy–Buckingham equation. The actual evapotranspiration (ET a) was calculated as follows: ET a = P − D + CR ±ΔH. During the study period, the amount of rainfall was 1406mm, 121mm greater than the historic average for the region (1285mm), with a notable peak in the month of January of 402mm (historic average: 251mm). The internal drainage was 300mm under T1, 352mm under T2, and 199mm under T3, and this was relevant during times with elevated P, when the actual H was greater than the field capacity H. The actual evapotranspiration (T1: −897.7mm, T2: −847.5mm, and T3: −970.8mm) and the water use efficiency (T1: −131.3kgmm−1, T2: −146.6kgmm−1, and T3: −127.5kgmm−1) did not differ among the treatments. The dispersion of D was greater than the other components of the water balance, especially during the period of elevated P, with the errors of this process propagated in the estimation of ET a. Despite of this propagated standard deviation of ET a, it accounted less than 15% of the total ET a, showing that the method may be conveniently used in field studies with sugarcane crops. [Copyright &y& Elsevier]

Abstract: Although mechanized harvesting of sugarcane can benefit the soil–environment system, successive harvests can compromise the physical soil quality. Information on the growth and distribution of the sugarcane root system and its relationship with physical soil properties are scarce in the literature. The objective of this study was to analyze the relationships between the spatial distribution of physical soil properties and sugarcane root density in a mechanically harvested area. The study was carried out in Jaboticabal, SP, Brazil in a Typic Kandiudox and with the SP81 3250 cultivar. Sugarcane plots were established in April 2005, and samples were taken from four trenches in July 2008 after three successive harvests. In each trench, 15 undisturbed soil samples were collected to evaluate bulk density (Ds), penetration resistance (Pr), total porosity (Tp) and moisture at field capacity (θ fc ), and 15 monoliths were collected to evaluate the root density (Rd), root length (Rl), root area (Ra) and root moisture (Rm) at different depths and plant locations. Soil moisture was balanced to the field capacity before Pr determination. The hypothesis that the sugarcane root system varied vertically and horizontally relative to the central axis of the plant and in relation to physical soil parameters was validated. Soil physical parameters varied significantly in the vertical direction, but sugarcane root system varied both vertically and horizontally. Ds values were 1.57, 1.55 and 1.39g cm−3 for layers between 0 and 0.2m, 0.2 and 0.4m and 0.4 and 0.6m, respectively. For the same layers, the Pr was 1.42, 1.20 and 0.87MPa. The largest Pr value (1.93MPa) was obtained near the surface in the space between rows. As Ds increased, Tp decreased and Pr increased. A consistent relationship was observed between Ds and Pr in all layers, and restrictions on root growth (Pr >2.0MPa) may occur when Ds ≥1.78gcm−3. The multivariate boundary line approach, in combination with nonlinear multiple regression analysis, successfully quantified the effects of Pr on Rd, Rl and Ra. Sugarcane root growth was not affected below Pr values of 0.75MPa, but decreased significantly between 0.75 and 2.0MPa. Root growth was severely restricted when Pr >2.0MPa. [Copyright &y& Elsevier]

Abstract: Leaching is disadvantageous, both for economical and environmental reasons since it may decrease the ecosystem productivity and may also contribute to the contamination of surface and ground water. The objective of this paper was to quantify the loss of nitrogen and sulfur by leaching, at the depth of 0.9m, in an Ultisol in São Paulo State (Brazil) with high permeability, cultivated with sugarcane during the agricultural cycle of crop plant. The following ions were evaluated: nitrite, nitrate, ammonium, and sulfate. Calcium, magnesium, potassium, and phosphate were also evaluated at the same depth. The sugarcane was planted and fertilized in the furrows with 120kgha−1 of N-urea. In order to find out the fate of N-fertilizer, four microplots with 15N-enriched fertilizer were installed. Input and output of the considered ions at the depth of 0.9m were quantified from the flux density of water and the concentration of the elements in the soil solution at this soil depth: tensiometers, soil water retention curve and soil solution extractors were used for this quantification. The internal drainage was 205mm of water, with a total loss of 18kgha−1 of N and 10kgha−1 of S. The percentage of N in the soil solution derived from the fertilizer (%NSSDF) was 1.34, resulting in only 25gha−1 of N fertilizer loss by leaching during all agricultural cycle. Under the experimental conditions of this crop plant, that is, high demand of nutrients and high incorporation of crop residues, the leached N represented 15% of applied N and S leaching were not considerable; the higher amount of leached N was native nitrogen and a minor quantity from N fertilizer; and the leached amount of Ca, Mg, K and P did not exceed the applications performed in the crop by lime and fertilization. [Copyright &y& Elsevier]