Long-term effects of lantana (Lantana spp. L.) residue additions on soil physical properties under rice–wheat cropping: I. Soil consistency, surface cracking and clod formation

Poor soil tilth is a major constraint in realizing optimum yield potential of wheat (Triticum aestivum L.) in rice (Oryza sativa L.)–wheat cropping system. The effect of long-term additions of lantana (Lantana spp. L.) biomass, a wild sage, on physical properties of a silty clay loam soil under rice–wheat cropping was studied in north-west India. Lantana was added to soil 10–15 d before puddling at 10, 20 and 30 Mg ha⁻¹ yr⁻¹ (fresh weight). At the end of 10th rice crop, liquid limit, plastic limit, shrinkage limit and plasticity index of soil increased significantly with lantana additions. The friability range of lantana-treated soil decreased from 8.9 to 7.8–8.2% gravimetric-moisture content, but soil became friable at relatively higher moisture content. Soil cracking changed from wide, deep cracks in hexagonal pattern to a close-spaced network of fine cracks. The cracks of sizes <5 mm increased, 10–20 mm and wider decreased, while 5–10 mm remained almost unchanged with lantana additions. The volume density of cracks decreased by 36–76% and surface area density by 19–37% compared with control. The clods of sizes <2 cm diameter increased, while 2–4 cm and 4–6 cm diameter decreased with lantana additions. The MWD of clods varied between 2.15 and 2.34 cm in lantana-treated soil as against 2.83 cm in the control. The bulk density and breaking strength of soil clods were lower in lantana-treated soil by 4–9% and 29–42% than in the control. About 23–47% less energy was required to prepare seed-bed in lantana-treated than in the control soil.     

Physical characterization of a soil amended with organic residues in a rice–wheat cropping system using a single value soil physical index

The effect of soil incorporations of lantana (Lantana spp.) biomass, an obnoxious weed, on physical environment of a silty clay loam soil (Typic Hapludalf) under rice (Oryza sativa L.)–wheat (Triticum aestivum L.) cropping was studied in a long-term field experiment conducted in a wet temperate region of north India. Fresh lantana biomass was incorporated into the plough layer at 10, 20 and 30 Mg ha⁻¹ annually, 7–10 days before puddling. Plant-available water capacity (PAWC), non-limiting water range (NLWR) and NLWR:PAWC ratio were determined to characterize soil physical environment during wheat crop in the tenth cropping cycle.

Ten annual applications of lantana at 10, 20 and 30 Mg ha⁻¹, increased organic carbon (OC) content over control by 12.6, 17.6 and 27.9% in 0–15 cm soil layer, and 17.1, 26.3 and 39.5% in 15–30 cm soil layer, respectively. The OC content in 0–15 and 15–30 cm soil layer of control plots was 11.1 and 7.6 g kg⁻¹ soil. Bulk density decreased by 3–14% in 7.5–10.5 cm layer and 1–6% in 15–18 cm layer. Volumetric moisture contents at 10% air-filled porosity were 38.4, 40.0, 54.5 and 55.7% at 7.5–10.5 cm depth, and 31.4, 32.2, 33.9 and 34.6% at 15–18 cm depth corresponding to 0, 10, 20 and 30 Mg ha⁻¹ lantana treatment, respectively. At 15–18 cm soil depth, volumetric moisture contents at 2 MPa soil penetration resistance were 26.9, 24.8, 23.0 and 19.6% in zero, 10, 20 and 30 Mg ha⁻¹ lantana-treated plots, respectively. Lower soil water contents associated with 10% air-filled porosity and greater soil water contents associated with a limiting penetration resistance of 2 MPa resulted in a lower NLWR (4.3%) for control as compared to lantana-treated soil (7.4–15.1%). The PAWC showed slight increase from 12.9 to 13.4–14.9% due to lantana additions. The NLWR:PAWC ratio was also lower in control (0.33) as compared to lantana-treated soil (0.55–1.01). The NLWR was significantly and positively correlated with wheat grain yield (r=0.858^**).     

Impact of water percolation on nutrient leaching from an irrigated paddy field in Japan

Abstract. We examined the effect on soil nutrient status and sustainability of water percolation through an irrigated paddy field in Japan, to the depth of drainage (40 cm). The difference between amounts of nutrients leached by percolation and those supplied by irrigation indicated that 25–130 kg ha⁻¹ Ca, 8–24 kg ha⁻¹ Mg, from −1 to 9 kg ha⁻¹ K, and 8–17 kg ha⁻¹ Fe, respectively, were lost each year from the 0–40 cm soil layer during rice cultivation, when the supply from fertilization and rainfall and the loss in grain harvest were not accounted for. When the supply of K from rainfall and the loss in grain harvest were taken into account, a total K loss of about 10 kg ha⁻¹ was estimated. The electrical neutrality of inorganic ions in the percolating water was always maintained. From these results we estimate that the amounts of exchangeable Ca and Mg in the soil to a depth of 40 cm would decrease by 50% within 50–260 and 30–100 years, respectively, if similar management were continued without fertilization. The total amount of carbon dioxide (ΣCO₂) leached in percolating water during the period of rice cultivation was 120–325 kg C ha⁻¹, which corresponded to 0.47–0.94% of the soil organic carbon to 40 cm depth.     

Assessing Passive Capillary-Wick Samplers for monitoring resident nitrate concentration in real field

Abstract. We evaluated the effectiveness of capillary-wick samplers (PCAPS) for continuous monitoring of resident nitrate concentration in three 'soil-crop-climate' systems differing in soil type, land use and climate. These systems involved: (i) acid silty soils under a beech-oak forest affected by heavy N-NH₄⁺ deposition in Belgium; (ii) silty soils under wheat cropping and a short rotation willow coppice plantation (SRC) in Belgium; and (iii) volcanic ash soils under plantain cultivation with and without urea fertilization in Colombia. The PCAPS continuously applied a suction of 0 to 5.4 kPa to the soil water below the effective rooting zone without the need for an auxiliary vacuum source. The nitrate concentrations showed large variations over time and ranged between 6–192 mg l^–1 under forest, 19–143 mg l^–1 under wheat, 11–47 mg l^–1 under SRC and 3–138 mg l^–1 under fertilized plantain. The analysis of the soil leachates collected with PCAPS confirms previous results dealing with leaching of nitrate and alkaline and alkaline-earth cations in similar 'soil-crop-climate' systems. It was concluded that PCAPS was a suitable tool to collect soil solutions and that it could help to assess nitrate leaching losses in various ecological or cropping conditions.     

Soil physical and hydraulic properties in a rice-wheat cropping system in India: effects of rice-straw management

Abstract. The effects of rice-straw management (incorporation, burning or removal) on soil organic carbon content and physical and hydraulic properties were determined after five years of rice–wheat cropping in a sandy loam soil in northwest India. Soil organic carbon content was greater with straw incorporation and straw burning than with straw removal, and aggregation status, total porosity, pore-size distribution, bulk density, dispersion ratio and soil strength were correspondingly improved. The treatment effects were confined mainly to the 0–5 cm depth. Water retention was less with straw burning than straw removal, owing to increased water repellency of the soil surfaces. Cumulative infiltration and its rate after five hours were greater with straw incorporation than straw burning or removal. Air entry values were unaffected by straw management; however, the values were greater after rice harvest than after wheat harvest.     

Effects of ridging on crop performance and symbiotic N2 fixation of fababean (Vicia faba L.)

Abstract. The success of organic cropping systems depends on symbiotic N₂ fixation by leguminous crops, and it is important to explore new management systems to improve the nitrogen input through N₂ fixation. During two growing seasons the possible advantage of growing fababean ( Vicia faba L.) in ridges was studied in comparison to the traditional method on flat soil. Differences in soil physical parameters resulted in a significantly greater microbial activity and a deeper root system at the flowering stage when grown in the ridge than on the flat. Consequently, the amount of fixed N at flowering was significantly greater in ridges than in flat soil. However, during the period from flowering until harvest, when the major part of the N uptake and N₂ fixation took place, the differences between the treatments disappeared. Average values for the growing season of fluorescein diacetate hydrolysis, arylamidase activity and arylsulphatase activity were significantly greater in the ridge than on the flat, and the microbial biomass-C, derived from substrate induced respiration (SIR), was on average 232 and 223 μg C g⁻¹ soil in the ridge and on the flat, respectively. Measured total-N uptake, including root N (0–30 cm depth), ranged from 206 to 247 kg N ha⁻¹, of which 182–201 kg N ha⁻¹ was fixed N. From 154 to 173 kg N ha⁻¹ was removed in grain resulting in a soil-N balance of +28 kg N ha⁻¹ in both years. However, by including estimates of total root N and rhizodeposition-N the soil-N balance ranged from +52 to +62 kg N ha⁻¹.     

Short-term kinetics of residual wheat straw C and N under field conditions: characterization by 13C15N tracing and soil particle size fractionation

Summary A clear understanding of the short-term decomposition and fate of crop residues is necessary to predict the availability of mineral N in soil. The fate of ¹³ C¹⁵N-labelled wheat straw in a silty soil (Typic Hapludalf) was studied using particle size fractionation and in situ incubation in which the equivalent of 8 t dry matter per ha of straw was incorporated into the soil over 574 days. Soil samples were separated into five particle-size fractions by wet sieving after disruption of aggregates. The weight, C and N contents, and ¹³C and ¹⁵N atom excess of each fraction were determined. Straw-derived C disappeared rapidly from the > 2000-μm fraction with an estimated half-life of 53 'normalized' days (equivalent of 10°C and −0−01 MPA water potential). Straw-derived C appeared to be only temporarily stored in the intermediate fractions (1000–2000 and 200–1000 pm). The maximum net ¹³C accumulation in the 50–200-μm fraction was 4·4% of added ¹³C. Straw-derived C accumulated most rapidly and preferentially in the 50-μm fraction, which stabilized after 265 days and accounted for 70% of the residual ¹³C on day 574. Although there was more residual ¹⁵N than ¹³C, the distributions and kinetics of the two isotopes in the fractions were similar.     

Formation of a Groundwater Table by Trench Irrigation and Evapotranspiration in a Drained Peatland

To evaluate the coexistence of agricultural managements and wetland ecosystem conservation, the Bibai mire, an ombrotrophic mire in Hokkaido, Japan, was selected as an experimental site that had been affected by neighboring agricultural managements. Since the lowering of the level of the groundwater table in the peripheral area of the mire had threatened indigenous vegetations, keeping the groundwater table shallow by trench irrigation seemed to be an effective measure to recover the original vegetation. The objective of the present study was to quantify the amount of water and the effective area of trench irrigation required in a bamboo-invading area in a pristine mire. We constructed a trench 28 m long and irrigated at the rate of 2.22 m³ d⁻¹ in a bamboo-invading area in the mire. And to analyze the hydro-meteorological conditions under the trench irrigation, we measured the saturated hydraulic conductivity of the peat layer (3.8 × 10⁻³ cm s⁻¹), the evapotranspiration rate (2.80 mm d⁻¹), the depth of the non-irrigated groundwater table (0.15 m) and the surface gradient (0.00493). In addition, using the mass conservation equation and Darcy's law, we derived a steady state model of the level of the groundwater table formed by trench irrigation, which required the five parameters mentioned above. The irrigated water spread over a distance of only about 15 m to both sides of the trench. The model also estimated that the distance for the irrigated area was 14.6 m and we concluded that the irrigated area was limited within a distance of 20 m distances to both sides of the trench and that the irrigation rate per unit trench length did not exceed 0.12 m² d⁻¹ for realistic values of the evapotranspiration rate and the saturated hydraulic conductivity in peatland.     

Field hydraulic properties of an Alfisol under various fallow systems in southwestern Nigeria

Abstract. The effects of various fallow management systems and cropping intensities on water infiltration were measured on an Alfisol at Ibadan in southwestern Nigeria. The objective was to determine the influence of the land use systems (a combination of crop–fallow sequences and intercropping types) on soil hydraulic properties obtained by disc permeameter and double-ring infiltration measurements. The experiment was established in 1989 as a split-plot design with four replications. The main plots were natural fallow, planted Pueraria phaseoloides and planted Leucaena leucocephala . The subplots were 1 year of maize/cassava intercrop followed by 3-year fallow (25% cropping intensity), or 2-year fallow (33% cropping intensity), or 1-year fallow (50% cropping intensity), or no fallow period (100% cropping intensity). Water infiltration rates and sorptivities were measured under saturated and unsaturated flow. Irrespective of land use, infiltration rates at the soil surface (121–324 cm h⁻¹) were greater than those measured at 30 cm depth (55–144 cm h⁻¹). This indicated that fewer large pores were present below 30 cm depth compared with 0–30 cm depth. Despite some temporal variation, sorptivities with the highest mean value of 93.5 cm h^−½ increased as the cropping intensity decreased, suggesting a more continuous macropore system under less intensive land use systems. This was most likely due to continuous biopores created by perennial vegetation under long fallow systems. Intercropped maize and cassava yields also increased as cropping intensity decreased. The weak relationship between crop yields and hydraulic conductivity/infiltration rates suggests that the rates were not limiting.     

Kinetic Parameters of Gross N Mineralization of Peat Soils as Related to the Composition of Soil Organic Matter

Peat land has been considered as an alternative type of land for agricultural development especially in the tropics. In the present study, the N-supplying capacity, one of the most important soil properties in terms of crop production, of peat soils was examined. Ten peat soil samples were collected from Indonesia, Malaysia, and Japan. Gross N mineralization in the soil samples was estimated using a zero-order model, and kinetic parameters of mineralization were determined using a simple type model. Soil organic matter composition was investigated using ¹³C CPMAS NMR. Mineralization potential ( N ₀), apparent activation energy ( E _a), and mineralization rate constant ( k ) ranged between 571–2,445 mg kg⁻¹, 281–8,181 J mol⁻¹, and 0.009–0.020 d⁻¹, respectively. Although none of the parameters showed a significant correlation with the soil C/N ratio, a negative correlation was observed between the k value and the ratio of the proportion of alkyl C in total C to that of O -alkyl C estimated by ¹³C CPMAS NMR. The latter suggested that the k values were higher in the peat soils relatively rich in readily decomposable organic matter including carbohydrates.     

Geologic Nitrogen as a Source of Soil Acidity

The origin of highly acidic (pH<4.5) barren soils in the Klamath Mountains of northern California was examined. Soil parent material was mica schist that contained an average of 2,700 mg N kg⁻¹, which corresponds to 7.1 Mg N ha⁻¹ contained in a 10-cm thickness of bedrock. In situ soil solutions were dominated by H⁺, labile-monomeric Al³⁺ and NO₃⁻, indicating that the barren area soils were nitrogen saturated—more mineral nitrogen available than required by biota. Leaching of excess NO₃⁻ has resulted in removal of nutrient cations and soil acidification. Nitrogen release rates from organic matter free soil ranged from 0.0163 to 0.0321 mg N kg⁻¹ d⁻¹. Nitrogen release rate from fresh ground rock was 0.0465 mg N kg⁻¹ d⁻¹. This study demonstrates that geologic nitrogen may represent a large and reactive nitrogen pool that can contribute significantly to soil acidification.     

Errors in the estimation of soil water properties and their propagation through a hydrological model

Abstract. The Agricultural Catchments Research Unit model (ACRU) includes a decision support system (DSS) for estimating the water content of soil at field capacity (θ _fc ) and wilting point (θ _wp ) when these characteristics are not directly measurable. Three methods of estimation are proposed: (a) based on silt and clay content and bulk density, (b) based on clay content only, and (c) based on soil series. These three pedotransfer functions are compared with respect to both the estimation of θ _fc and θ _wp and the propagation of errors when the actual evapotranspiration of a wheat crop (E) is predicted over the growing season by the ACRU model.
The standard error of estimation was between 0.066 and 0.082 m³/m³ for θ _fc , between 0.056 and 0.069 m³/m³ for θ _wp and between 29.9 and 34.8 mm of water for E. The method based on silt and clay contents and bulk density predicted θ _fc and θ _wp for non-swelling soils most precisely. The method based on soil series was better than other methods for swelling soils. It also performed better for estimating available water capacity and consequently for predicting E from a conceptual soil water model. The propagated error of estimating θ _fc and θ _wp using the DSS reached 15–18% of the simulated E. The error in the prediction of E can reach 26–30% when spatial variation in soil properties is also estimated.     

Computer simulation of winter leaching losses of nitrate from soils cropped with winter wheat

Abstract. A computer simulation model was used to estimate the effects of season, site, sowing date, residual-N after harvest, autumn-N and field drains on winter losses of nitrate from soils growing winter wheat. The simulations were based on weather data between 1970–71 and 1983–84 and soil data from Rothamsted and Woburn. The residual-N after harvest was predicted to have most effect on nitrate losses, followed by season and site. For the values of residual-N and autumn-applied fertilizer-N tested, the predicted average nitrate-N losses differed between seasons by up to 100 kg N ha^-1, and the nitrate-N concentrations varied between 30 and 80 mg N l^-1.     

Puddling and N management effects on crop response in a rice-wheat cropping system

Coarse-textured soils are puddled to reduce high percolation losses of irrigation water under rice (Oryza sativa L.). This practice, however, reduces yield of succeeding wheat (Triticum aestivum L.) owing to deterioration in soil physical conditions. The 6 year field study reported in this paper evaluated the effects of puddling level and integrated N management on the development of subsurface compaction and growth and yield of rice and the following spring wheat grown in 1 year sequence on a sandy loam soil. Treatments were combinations of three puddling levels: low (one discing and one planking), medium (two discings and one planking), and high (four discings and one planking), and three nitrogen sources: (1) 120 kg N ha⁻¹ from urea, (2) 60 kg N ha⁻¹ from urea plus sesbania (Sesbania aculeata Pers.) green manure, and (3) 60 kg N ha⁻¹ from urea plus 20 Mg ha⁻¹ farmyard manure. Percolation rate decreased from 14 mm day⁻¹ with low puddling to 10 mm day⁻¹ with high puddling, with a corresponding reduction in irrigation water requirement of rice of about 20%. Bulk density profiles in the 0–30 cm soil layer showed the formation of a compact layer at 15–20 cm depth, and bulk density increased with puddling level and cropping season. The impact of organic amendments in reducing bulk density was immediate, but the rate of increase in bulk density with time was the same in all the nitrogen sources. Organic amendments did not affect percolation rate and irrigation requirement of rice. Rice yields were not significantly affected by puddling and N source treatments throughout the study period. Residual effects of treatments on wheat yield were observed from the second season onwards. Interactive effects of puddling and N source on yields of rice and succeeding wheat were not significant. Yield differences in wheat between high and low puddling were 8% and 11% during the second and the fifth cropping season, respectively. This study indicates that medium puddling was optimum, as it reduced percolation without decreasing yield of succeeding wheat.     

Effect of soil compaction by tractor traffic on soil structure, denitrification, and yield of wheat (Triticum aestivum L.)

In a field experiment with soil compaction by tractor traffic on a loam soil, the denitrification rate (using the C₂H₂ inhibition method), the soil structure, and the wheat yield were investigated. Tractor traffic on wet soil (> – 50 mbar matric potential) reduced the pore volume, doubled the percentage of large aggregates (> 20 mm), reduced the wheat yield by about 25%, and increased the N-loss through denitrification by a factor of 3–4. Neither of these parameters were affected by tractor traffic at low soil moisture content. The weight of the tractor (1800 kg vs 4800 kg) did not significantly alter the effect of compaction on the measured parameters. There was a factor of 2–6 between the measured denitrification rate in compacted and that in uncompacted soil, and this factor showed little dependence on the average activity level on each date of measurement. Accumulated values for the measured denitrification during 75 days (May 23-August 9) were 3–5 kg N ha^–1 in uncompacted soil and 15–20 kg N ha^–1 in soil which was compacted in wet condition.     

The effect of soil texture and soil drainage on emissions of nitric oxide and nitrous oxide

Abstract. Agricultural soils are important sources of the tropospheric ozone precursor NO and the greenhouse gas N₂O. Emissions are controlled primarily by parameters that vary the soil mineral N supply, temperature and soil aeration. In this field experiment, the importance of soil physical properties on emissions of NO and N₂O are identified. Fluxes were measured from 13 soils which belonged to 11 different soil series, ranging from poorly drained silty clay loams to freely drained sandy loams. All soils were under the same soil management regime and crop type (winter barley) and in the same maritime climate zone. Despite this, emissions of NO and N₂O ranged over two orders of magnitude on all three measurement occasions, in spring before and after fertilizer application, and in autumn after harvest. NO emissions ranged from 0.3 to 215 μg NO-N m^–2 h^–1, with maximum emissions always from the most sandy, freely drained soil. Nitrous oxide emissions ranged from 0 to 193 μg N₂O-N m^–2 h^–1. Seasonal shifts in soil aeration caused maximum N₂O emissions to switch from freely drained sandy soils in spring to imperfectly drained soils with high clay contents in autumn. Although effects of soil type on emissions were not consistent, N₂O emission was best related to a combination of bulk density and clay content and the NO/N₂O ratio decreased logarithmically with increasing water filled pore space.     

Sequential extraction methods for soil organic nitrogen

(pp. 825–831)
This study was carried out to clarify the effects of soil nitrate before cultivation and amounts of basal-dressed nitrogen on additional N application rate and yields of semi-forced tomato for three years from 1998 to 2000. The amounts and timing of additional N dressing were determined based on diagnosis of petiole sap nitrate. The top-dressing was carried out with a liquid fertilizer when the nitrate concentration of a leaflet's petiole sap of leaf beneath fruit which is 2–4 cm declined below 2000 mg L⁻¹.
For standard yield by the method of fertilizer application based on this condition, no basal-dressed nitrogen was required when soil nitrate before cultivation was 150 mg kg⁻¹ dry soil or higher in the 0–30 cm layer; 38 kg ha⁻¹ of basal-dressed nitrogen, which corresponds to 25% of the standard rate of fertilizer application of Chiba Prefecture, was optimum when soil nitrate before cultivation was 100150 mg kg⁻¹ dry soil; 75 kg ha⁻¹ of basal-dressed nitrogen, which corresponds to 50% of the standard, was optimum when soil nitrate before cultivation was under 100 mg kg⁻¹ dry soil. A standard yield was secured and the rate of nitrogen fertilizer application decreased by 49–76% of the standard by keeping the nitrate concentration of tomato petiole sap between 1000–2000 mg L⁻¹ from early harvest time to topping time under these conditions.     

Methane consumption in a frequently nitrogen-fertilized and limed spruce forest soil after clear-cutting

Abstract. The effects of especially frequent nitrogen (N) additions (from 1959 to 1986, totalling 860 kg N ha⁻¹) and liming (in 1958 and 1980, totalling 6000 kg CaCO₃ ha⁻¹) on CH₄ uptake by a boreal forest soil were studied in a stand of Norway spruce. Except for a forested reference plot, the stand was clear-cut in January 1993 and the following year one-half of each clear-cut plot was prepared by mounding. Fluxes of CH₄ were measured with static chambers in the autumn before clear-cutting and during the following four summers. The average CH₄ uptake during 1993–96 in the forested reference plot was 82 μg CH₄ m⁻² h⁻¹(ranging from 10 to 147 units). In the first summer after clear-cutting, the cleared plot showed 42% lower CH₄ uptake rate than the forested reference plot, but thereafter the difference became less pronounced. The short-term decrease in CH₄ consumption after clear-cutting was associated with increases in soil NH₄⁺ and NO₃⁻concentrations. Mounding tended at first to stimulate CH₄ uptake but later to inhibit it. Neither liming nor N-fertilization had significant effects on CH₄ consumption. Our results suggest that over the long term, in N-limited upland boreal forest soils, N addition does not decrease CH₄ uptake by the soil.     

The topology of pore structure in cracking clay soil I. The estimation of numerical density

The numerical density, N_v , of the pore structure of soil is the number of disjoint networks of pores per unit volume of soil. A method is described for estimating N_v of patterns of cracks that dominate in many clay subsoils. The cracks are photographed from numerous close-spaced parallel sections and skeletonized; by comparing the skeletonized photographs sequentially, individual networks are tracked from one section to another and counted. The average number of networks that appears or disappears per section in the sequence is a measure of the numerical density and is obtained by regressing the counts on the volume of soil spanned by the sections. The regressions for appearances and disappearances converge on one another and stabilize within 10 to 20 sections, so that N_v can be estimated for a sample of soil with moderate effort.
Estimates of N_v for cracks wider than 60 μm in subsoil of the Windsor series, sampled at two nearby sites and 5 years apart in time and determined from sections at 50 μm intervals, were approximately 32 cm⁻³ and 36cm⁻³. That of N_v in the Swanwick series subsoil nearby was about 75 cm⁻³.