Deforestation and land-use effects on soil degradation and rehabilitation in western Nigeria. I. Soil physical and hydrological properties

Assessments of the effects of deforestation, post-clearance tillage methods and farming systems treatments on soil properties were made from 1978 through 1987 on agricultural watersheds near Ibadan, southwestern Nigeria. These experiments were conducted in two phases: Phase I from 1978 through 1981 and Phase II from 1983 to 1987, with 1 year (1982) as a transition phase when all plots were sown with mucuna (Mucuna utilis). There were six treatments in Phase I involving combinations of land clearing and tillage methods: (1) manual clearing with no-till (MC-NT); (2) manual clearing with plough-till (MC-PT); (3) shear-blade clearing with no-till (SB-NT); (4) tree-pusher/root rake clearing with no-till (TP-NT); (5) tree-pusher/root-rake clearing with plough-till (TP-PT); (6) traditional farming (TF). The six treatments were replicated twice in a completely randomized design. The traditional treatment of Phase I was discontinued during Phase II. The five farming systems studied during Phase II with a no-till system in all treatments were: (1) alley cropping with Leucaena leucocephala established on the contour at 4-m intervals; (2) and (3) fallowing with Mucuna utilis on severely degraded and moderately degraded watersheds, respectively, for 1 year followed by maize-cowpea rotation for another; (4) and (5) ley farming involving establishment of pasture in the first year on severely and moderately degraded plots, respectively, controlled grazing in the second year, and growing maize (Zea mays)-cowpea (Vigna unguiculata) in the third year. All treatments, imposed on watersheds of 2–4 ha each, were replicated twice. The soil properties analyzed were particle size distribution, total aggregation and mean weight diameter of aggregates, soil bulk density, penetrometer resistance, water retention characteristics, infiltration capacity and saturated hydraulic conductivity. These properties were measured under the forest cover in 1978, and once every year during the dry season thereafter during Phases I and II. Prior to deforestation, mean soil bulk density was 0·72 Mg m⁻³ and 1·30 Mg m⁻³, soil penetration resistance was 32·4 KPa and 90·7 KPa, and mean weight diameter of aggregates was 3·7 mm and 3·2 mm for 0–5 cm and 5–10 cm depths, respectively. The infiltration rate was excessive (54–334 cm hr⁻¹) and saturated hydraulic conductivity was rapid (166–499 cm hr⁻¹) under the forest cover. Furthermore, water transmission properties varied significantly even over short distances of about 1 m. Deforestation and cultivation increased soil bulk density and penetration resistance but decreased mean weight diameter of aggregates. One year after deforestation in 1980, mean soil bulk density was 1·41 Mg m⁻³ for 0–5 cm depth and 1·58 Mg m⁻³ for 5–10 cm depth. Soil bulk density and penetration resistance were generally higher for NT than for PT methods, and the penetration resistance was extremely high in all treatments by 1985. During Phase II, soil bulk density was high during the grazing cycle of the ley farming treatment. Sand content at 0–5 cm depth increased and clay content decreased with cultivation duration. Soon after deforestation, saturated hydraulic conductivity and equilibrium infiltration rate in cleared and cultivated land declined to only 20–30 per cent of that under forest. Mean saturated hydraulic conductivity following deforestation was 46·0 cm hr⁻¹ for 0–5 cm depth and 53·7 cm hr⁻¹ for 5–10 cm depth. Further, infiltration rate declined with deforestation and cultivation duration in all cropping systems treatments. During Phase I, mean infiltration rate was 115·8 cm hr⁻¹ under forest cover in 1978, 20·9 cm hr⁻¹ in 1979, 17·4 cm hr⁻¹ in 1980 and 20·9 cm hr⁻¹ in 1981. During Phase II, mean infiltration rate was 8·5 cm hr⁻¹ in 1982, 11·9 cm hr⁻¹ in 1983, 11·0 cm hr⁻¹ in 1984, 11·3 cm hr⁻¹ in 1985 and 5·3 cm hr⁻¹ in 1986. Infiltration rate was generally high in ley farming and mucuna fallowing treatments. Natural fallowing drastically improved the infiltration rate from 19·2 cm hr⁻¹ in 1982 to 193·2 cm hr⁻¹ in 1986, a ten-fold increase within 5 years of fallowing. High-energy soil water retention characteristics in Phase I were affected by those treatments that caused soil compaction by mechanized clearing and no-till systems. Soil water retention at 0·01 MPa potential in 1979 was 19·2 per cent (gravimetrics) for SB, 17·9 per cent for TP, 15·9 per cent for MC and 17·8 per cent for TF methods. With regards to tillage, soil water retention was 17·8 per cent for NT compared with 16·8 per cent for PT. During Phase II, water retention characteristics were not affected by the farming system treatments. Mean soil water retention (average of 4 years' data from 1982 to 1986) at 0·01 MPa for 0–5 cm depth was 16·6 per cent for alley cropping, 16·7 per cent for mucuna fallowing and 16·8 per cent for ley farming. Mean soil water retention for 1·5 MPa suction was 9·3 per cent for alley cropping, 8·7 per cent for mucuna fallowing, and 9·3 per cent for ley farming. Water retention at 1·5 MPa suction correlated with the clay and soil organic carbon content.     

Effects of cropping systems on nitrogen,phosphorus and potassium forms and soil organic carbon in a Gray Luvisol

The effects of up to 23 years of agricultural cropping of a boreal forest soil on soil organic carbon (SOC) and N, P, and K pools were studied. The cropping systems studied were: (a) continuous barley, (b) continuous forage bromegrass, (c) continuous forage legume, and (d) barley/grass-legume forage rotation. Continuous bromegrass increased while other cropping systems decreased SOC in the surface soil. Kjeldahl N in soil approximately followed the trend in SOC. The net gain in N under continuous grass was attributed mostly to nonsymbiotic N fixation. Changes in SOC content appeared to be also influenced by cropping and tillage frequencies. Changes in fixed (intercalary) ammonium were small. There was no measurable change in total P, in part, because input was only slightly higher than crop offtake. Organic P increased under continuous bromegrass, and tended to decrease under continuous legume. The C/N and C/P ratios of soil organic matter decreased slightly with cropping. Exchangeable K (K_ex) was decreased by cropping systems containing a legume crop to a greater extent than those without a legume crop. Most of the decrease occurred in the 0–15 cm depth. Nitric acid extractable K was not affected by cropping. Since net loss of K_ex to 30 cm depth was substantially less than crop offtake, it is suggested that subsoil K reserves and matrix K were supplying a major portion of the crops' K requirement. It is concluded that the effects of cropping systems on SOC, N, P and K are influenced by crop type, and cropping and tillage frequencies.     

Characterizing the soil moisture regime of a Typic Haplohumod

The saturated hydraulic conductivities (K_sat) of 22 spodic horizons with and without a thin iron pan, were measured in situ with a new technique, using large, carved-out columns, encased in gypsum. Measured infiltration rates and pressure heads above and below the spodic horizons allowed calculation of K_sat, which averaged 8 cm d^?1. Flow rates averaged 32 cm d^?1, however, due to a hydraulic head gradient across the spodic horizon of 4 cm cm^?1. Occurrence of a thin iron pan in the spodic horizon did not affect its K_sat-value. The measured high flow rates exclude the occurrence of perched watertables. Lateral flow of water, forming surface ponds in local depressions, was due to surface runoff, rather than to lateral movement of perched water: surface ponding of water occurred also in soils in which the spodic horizon had been mixed by tillage.     

Change of dry bulk density and Ksat after incubation of a soil in the presence of organic amendments

Abstract

Kamouraska Ap horizon samples were incubated in the presence of organic amendments, peat moss, straw, compost and green manure, applied at a rate equivalent to 7.5 t of carbon/ha. Water was added to reach 80% of field capacity. The soil‐amendement mixtures were incubated at 37°C for periods of 4, 8, 16, 32 or 64 weeks. Settling tests were performed using a jolting volumeter. Minimum dry bulk density (mDBD), saturated hydraulic conductivity (K_sat) and water content at field capacity were determined. For the unamended soil, mDBD corresponded to 1.1 g.cm^‐3 and K_{sat max} to 265 cm/h. After incubation, mDBD varied from 1.02 to 1.12 g.cm^‐3 and K_{sat max} values were generally below 150 cm/h. The results were discussed in relation to the decomposition of the organic amendments and the formation of stable aggregates.     

Aspartase Activity of Soils Under Different Management Systems

Abstract

Recent interest in soil tillage, cropping systems, and residue management has focused on low‐input sustainable agriculture. This study was carried out to evaluate the effects of various management systems on aspartase activity in soils. This enzyme [L‐aspartate ammonia‐lyase, EC 4.3.1.1] catalyzes the hydrolysis of L‐aspartate to fumarate and NH₃. It may play a significant role in the mineralization of organic N in soils. The management systems consisted of three cropping systems [continuous corn (Zea mays L.) (CCCC); corn‐soybean [Glycine max (L.) Merr.]‐corn‐soybean (CSCS); and corn‐oat (Avena sativa L.)‐meadow‐meadow (COMM) {meadow was a mixture of alfalfa (Medicago sativa L.) and red clover (Trifolium pratense L.)] at three long‐term field experiments initiated in 1954, 1957, and 1978 in Iowa and sampled in June 1987. The plots received 0 or 180 (or 200) kg ha^?1 before corn and an annual application of 20 kg P and 56 kg K ha^?1. The tillage systems (no‐tillage, chisel plow, and moldboard plow) were initiated in 1981 in Wisconsin and sampled in May 1991. The crop residue treatments were: bare, normal, mulch, and double (2×) mulch. The residue in the study was corn stalks. Results showed that, in general, crop rotation in combination with N fertilizer treatments affected aspartase activity in the following order: COMM>CSCS>CCCC. Because of nitrification of the NH₄ ⁺ or NH₄ ⁺‐forming fertilizers, which resulted in decreasing the pH values, N fertilizer application, in general, decreased the aspartase activity in soils in the order: CCCC>CSCS>COMM. The effect of tillage and residue management practices on aspartase activity in soils showed a very wide variation. The trend was as follows: no‐till/2× mulch>chisel plow/mulch>moldboard plow/mulch>no‐till normal>chisel plow/normal>no‐till bare>moldboard plow/normal. Aspartase activity decreased with increasing depth in the plow layer (0–15 cm) of the no‐till/2× mulch. The decreased activity was accompanied by decreasing organic C and pH with depth. Statistical analyses using pooled data (28 samples) showed that aspartase activity was significantly, linearly correlated with organic C (r=0.78^***) and exponentially with soil pH (r=0.53**). The variation in the patterns and magnitudes of activity distribution among the profiles of the four replicated plots was probably due to the spatial variability in soils.     

Effects of charcoal production on soil physical properties in Ghana

Charcoal production, widespread in Ghana like in other W African countries, is a major driver of land‐cover change. Effects of charcoal production on soil physical, including hydrological, properties, were studied in the forest–savannah transition zone of Ghana. Core and composite samples from 12 randomly selected sites across the width of Kotokosu watershed were taken from 0–10 cm layer at charcoal‐site soils and adjacent field soils (control). These were used to determine saturated hydraulic conductivity (K_sat), bulk density, total porosity, soil texture, and color. Infiltration rates, surface albedo, and soil‐surface temperature were also measured on both sites. The results showed that the saturated hydraulic conductivity of soils under charcoal kilns increased significantly (p < 0.01) from 6.1 ± 2.0 cm h^–1 to 11.4 ± 5.0 cm h^–1, resulting to a relative increase of 88%. Soil color became darkened under charcoal kilns with hue, value, and chroma decreasing by 8%, 20%, and 20%, respectively. Bulk density on charcoal‐site soils reduced by 9% compared to adjacent field soils. Total porosity increased from 45.7% on adjacent field soils to 50.6% on earth kilns. Surface albedo reduced by 37% on charcoal‐site soils while soil‐surface temperature increased up to 4°C on average. Higher infiltration rates were measured on charcoal‐site soils, which suggest a possible decrease in overland flow and less erosion on those kiln sites.     

Spatial and temporal variability of some soil physical properties following tillage of a Nigerian Paleustult

The objective of this study was to evaluate quantitatively the magnitude of the spatial and temporal variation for 7 soil physical properties on a conventionally-tilled Nigerian Paleustult. A 0.4-ha plot was disc-ploughed, disc-harrowed twice, subjected to tractor-wheel traffic at regular space intervals and then seeded to maize (Zea mays, L.). There were significant differences in the physical properties owing to tillage position (spatial variability) and date of sampling (temporal variability), more so in the 0–10-cm layer than in the 10–20-cm layer. In the surface layer, bulk density (Db) and penetrometer resistance (PR) were significantly higher (P ⩽ 0.01) along the tyre marks (maximum Db = 1.76 Mg m⁻³) than in the uncompacted crop row (maximum Db = 1.35 Mg m⁻³) and interrow positions (maximum Db = 1.46 Mg m⁻³). Saturated hydraulic conductivity (K_sat), total porosity (TP) and macroporosity (M) were significantly lower along the tyre mark than in the crop row and interrow positions. K_sat ranged from 0.6 to 42.8 cm h⁻¹, TP, from 0.34 to 0.50 cm³ cm⁻³ and M from 0.06 to 0.25 cm³ cm⁻³ along the tyre mark and crop row positions, respectively. Significant temporal changes were noticed only in K_sat, soil moisture content (MC) and PR. K_sat increased steadily with time along the tyre mark, but showed an irregular trend in the other two positions. PR did not change with time along the tyre marks but it increased significantly with time along the other two positions. MC changed according to the periodicity of rainfall. Only TP varied, owing to tillage position × date interaction. The 10–20-cm layer was spatially less variable but temporally more viarable than the surface layer. Only K_sat and PR showed significant changes owing to the tillage positions, but Db, K_sat, PR and moisture retained at 10 kPa suction (τv10) showed significant temporal changes. Only τv110 varied owing to position × date interaction in this layer.     

Performance assessment of nanoparticulate lime to accelerate the downward movement of calcium in acid soil

Calcium in conventional lime (CL) moves downward extremely slowly into the soil in the short term. To monitor the effects of using nanoparticulate lime (NL) in low affordable doses and in large doses on accelerating the downward movement of Ca in a simulated plough layer profile (0–25 cm), we ran a column leaching experiment with an acid soil with NL applied into the top 5 cm. The experiment evaluated a reference treatment (0 NL), three low doses of NL (8, 40 and 80 kg ha^?1 = 0.02×, 0.1×, and 0.2× the NL needed to raise soil pH to 6.0 in the top 5 cm: NLR_pH‐6), and two large doses (400 and 800 kg ha^?1 = 1× and 2× NLR_pH‐6). Over the short term (70 days), NL accelerated the downward movement of Ca, likely by mass flow of nanoparticles down soil micro‐ and macropores. Applying NL to the top 5 cm at 40 and 80 kg ha^?1 was effective at increasing the downward movement of Ca and the neutralization of soil acidity (in terms of pH) to 20 cm depth, as well as rectifying Al toxicity (in terms of exchangeable Al) to ≤ the critical limit to 10 cm. NL at 80 kg ha^?1 was most economically justified in terms of rectifying Al toxicity throughout the profile. Therefore, NL may introduce new and alternative application strategy that allowing lower rates of lime to be used and thereby offset economic constraints posed by high application rates.     

Assessment of long-term barley–legume rotations in a typical Mediterranean agro-ecosystem: grain and straw yields

Traditional Mediterranean rainfed cereal/fallow systems are being replaced by cereal monoculture due to land-use pressure. Food or forage legumes in rotation with cereals are an alternative sustainable cropping system. Complex cropping systems can only be assessed by long-term trials. This 11-year rainfed barley-based rotation trial in northern Syria assessed rotation effects on yields of barley and legumes, with particular emphasis on the management of vetch. The mean order of barley grain yields from the rotations was: vetch for hay, vetch for grazing > fallow = medic = vetch for seed > lentil, and continuous barley. Straw yields followed a similar pattern. Nitrogen (60 kg ha^?1) increased grain (39%) and straw (65%) yields. The N fertilization of barley had no carryover effect on the alternative legume crops. Although there were no significant differences in seed or straw yield between lentil and vetch, seasonal rainfall influenced overall yields. Total biomass yields were in the order of vetch, medic and lentil. There is a compelling case for annual vetch paired with barley in rotations for the Mediterranean region. Thus, barley/vetch rotations can potentially enhance barley yields and improve soil quality, and provide valuable fodder for small ruminants as well in the region's agricultural systems.     

The effect of soil phosphorus on particulate phosphorus in land runoff

Accumulation of surplus phosphorus (P) in the soil and the resulting increased transport of P in land runoff contribute to freshwater eutrophication. The effects of increasing soil P (19–194 mg Olsen‐P (OP) kg⁻¹) on the concentrations of particulate P (PP), and sorption properties (Q_max, k and EPCo) of suspended solids (SS) in overland flow from 15 unreplicated field plots established on a dispersive arable soil were measured over three monitoring periods under natural rainfall. Concentrations of PP in plot runoff increased linearly at a rate of 2.6 μg litre⁻¹ per mg OP kg⁻¹ of soil, but this rate was approximately 50% of the rate of increase in dissolved P (< 0.45 μm). Concentrations of SS in runoff were similar across all plots and contained a greater P sorption capacity (mean + 57%) than the soil because of enrichment with fine silt and clay (0.45–20 μm). As soil P increased, the P enrichment ratio of the SS declined exponentially, and the values of P saturation (P_sat; 15–42%) and equilibrium P concentration (EPCo; 0.7–5.5 mg litre⁻¹) in the SS fell within narrower ranges compared with the soils (6–74% and 0.1–10 mg litre⁻¹, respectively). When OP was < 100 mg kg⁻¹, P_sat and EPCo values in the SS were smaller than those in the soil and vice‐versa, suggesting that eroding particles from soils with both average and high P fertility would release P on entering the local (Rosemaund) stream. Increasing soil OP from average to high P fertility increased the P content of the SS by approximately 10%, but had no significant (P > 0.05) effect on the P_sat, or EPCo, of the SS. Management options to reduce soil P status as a means of reducing P losses in land runoff and minimizing eutrophication risk may therefore have more limited effect than is currently assumed in catchment management.     

Improving dryland cropping system nitrogen balance with no‐tillage and nitrogen fertilization

Studies on N balance due to N inputs and outputs and soil N retention to measure cropping system performance and environmental sustainability are limited due to the complexity of measurements of some parameters. We measured N balance based on N inputs and outputs and soil N retention under dryland agroecosystem affected by cropping system and N fertilization from 2006 to 2011 in the northern Great Plains, USA. Cropping systems were conventional tillage barley (Hordeum vulgaris L.)–fallow (CTB‐F), no‐tillage barley–fallow (NTB‐F), no‐tillage barley–pea (Pisum sativum L.) (NTB‐P), and no‐tillage continuous barley (NTCB). In these cropping systems, N was applied to barley at four rates (0, 40, 80, and 120 kg N ha^?1), but not to pea and fallow. Total N input due to N fertilization, pea N fixation, soil N mineralization, atmospheric N deposition, nonsymbiotic N fixation, and crop seed N and total N output due to grain N removal, denitrification, volatilization, N leaching, gaseous N (NO_x) emissions, surface runoff, and plant senescence were 28–37% greater with NTB‐P and NTCB than CTB‐F and NTB‐F. Total N input and output also increased with increased N rate. Nitrogen accumulation rate at the 0–120 cm soil depth ranged from –32 kg N ha^?1 y^?1 for CTB‐F to 40 kg N ha^?1 y^?1 for NTB‐P and from –22 kg N ha^?1 y^?1 for N rates of 0 kg N ha^?1 to 45 kg N ha^?1 y^?1 for 120 kg N ha^?1. Nitrogen balance ranged from 1 kg N ha^?1 y^?1 for NTB‐P to 74 kg N ha^?1 y^?1 for CTB‐F. Because of increased grain N removal but reduced N loss to the environment and N fertilizer requirement as well as efficient N cycling, NTB‐P with 40 kg N ha^?1 may enhance agronomic performance and environmental sustainability while reducing N inputs compared to other management practices.     

Experimental and numerical study of water flow in soil under irrigation in northern Senegal: evidence of air entrapment

Irrigation by surge flooding does not always wet the soils thoroughly, and we have investigated the reasons for this on an irrigated plot in northern Senegal by monitoring the water budget during a rice cropping season (100 days). The amount of water added during each irrigation event was measured, and evapotranspiration and infiltration were estimated with lysimeters and Muntz infiltration rings, respectively. At the same time, piezometric levels, neutron probe values and water tension data were recorded at two stations in the plot. These measurements showed unusual results: infiltration rate was less than 1 × 10^?6 mm s^?1 (less than 0.1 mm a day), there was a constant water deficit during the entire irrigation period, around 50 cm deep, and tensiometers at 40 cm reacted very slowly to water infiltration. The water fluxes in the vadose zone derived from these data showed clearly a discrepancy between fluxes calculated from hydraulic gradients and fluxes calculated from mass conservation. The hydraulic gradients suggested a zero flux plane at 40 cm below the surface, but the calculated values of the fluxes overestimated by several orders of magnitude the infiltration rates determined on the plot, whereas fluxes determined from mass conservation matched far better. These results show that air was entrapped between the shallow water table and the wetting front, and this inhibited water infiltration. Modelling water flow down the soil profile with a computer program for simulating one‐dimensional water movement (Hydrus) confirmed that single‐phase models cannot describe imbibition in this situation. Simple infiltration models based on a modified Green–Ampt equation accounting for air compression and air counter‐flow, however, fit experimental infiltration data much better. We demonstrated that where surge flooding is associated with a shallow water table, as in many large irrigation schemes, one must take into account the presence of air to quantify the flow of water into the soil.     

Molecular Characteristics Influencing Retrogradation Kinetics of Rice Amylopectins

The enthalpy changes (ΔH) for melting of crystallites formed during retrogradation of 60% (w/w) amylopectins (AP) aged at 4°C were investigated using AP from 13 rice cultivars with well‐known structural properties. According to the Avrami equation, the resultant kinetic parameters for AP retrogradation were obtained in relation to structural factors. Generally, the AP systems studied showed two stages of retrogradation behavior during early (≤7 days) and late (≥7 days) storage. The Avrami exponent for early‐stage kinetics (n₁, 1.04–5.54) was greater than the corresponding value for late‐stage kinetics (n₂, 0.28–1.52). While the Avrami K constant of the early‐stage kinetics (K₁, 1.0×10^‐5 to 2.3×10^‐1 day^‐n) was lower than the corresponding value of late‐stage kinetics (K₂, 4.4×10^‐2 to 1.4 day^‐n). The ΔH values for late and infinite retrogradation stages showed a significantly positive correlation with the proportions of short chain (chain length [CL] ≤ 15 glucose units) and long chain (CL = 16–100 glucose units) fractions, respectively. Retrogradation of AP with a higher number‐average degree of polymerization, greater proportion of short chain fractions, and shorter average chain lengths revealed significantly greater n₁ values and smaller K₁ values. Values for n₂ and K₂ showed little influence from the molecular properties except for the proportion of extra long (CL>100 glucose units) and long chain fractions on K₂. The negatively linear relationships between log K and n suggest the importance of some nonstructural factors for AP retrogradation mechanisms in various starch systems.     

Nitrous oxide release from arable soil: importance of perennial forage crops

 N₂O emission rates from a sandy loam soil were measured in a field experiment with 2 years of perennial forage crops (ryegrass, ryegrass-red clover, red clover) and 1 year of spring barley cultivation. Spring barley was sown after the incorporation of the forage crop residues. All spring barley plots received 40 kg N ha^–1 N fertiliser. Ryegrass, ryegrass-red clover and red clover plots were fertilised with 350 kg N ha^–1, 175 kg N ha^–1 and 0 kg N ha^–1, respectively. From June 1994 to February 1997, N₂O fluxes were continuously estimated using very large, closed soil cover boxes (5.76 m²). In order to compare the growing crops, the 33 months of investigation were separated into three vegetation periods (March–September) and three winter periods (October–February). All agronomic treatments (fertilisation, harvest and tillage) were carried out during the vegetation period. Large temporal changes were found in the N₂O emission rates. The data were approximately log-normally distributed. Forty-seven percent of the annual N₂O losses were observed to occur during winter, and mainly resulted from N₂O production during daily thawing and freezing cycles. No relationship was found between the N₂O emissions during the winter and the vegetation period. During the vegetation period, N₂O losses and yields were significantly different between the three forage crops. The unfertilised clover plot produced the highest yields and the lowest N₂O losses on this soil compared to the highly fertilised ryegrass plot. Total N₂O losses from soil under spring barley were higher than those from soil under the forage crops; this was mainly a consequence of N₂O emissions after the incorporation of the forage crop residues. Received: 31 October 1997     

Effects of land use change and seasonal variation in the hydrophysical properties in Vertisols in northeastern Mexico

The impact of the use of natural resources associated with anthropogenic activities has increased evidently, mainly through land use changes which have altered hydrophysical properties of soils. We hypothesized that, in the same soil type (Vertisol), four types of land use system (grassland, agricultural, Eucalyptus plantation and thornscrub) and seasonal variation can modify the soil hydrophysical properties. Results showed significant differences between land use systems and seasons for hydraulic conductivity (K), infiltration capacity (fp) and cumulative infiltration (fc). There were no seasonal differences in soil penetration resistance (SPR), bulk density (ρd) and total porosity (φP). Grassland presented higher values for ρd (1.2 g cm^?3) and SPR (5.3 kg cm^?2) and lower for K (0.8 × 10^?5 cm s^?1) and φP (53%), unlike thornscrub. Agriculture presented lower SPR (0.4 kg cm^?2), while plantation showed similar values when compared to the thornscrub. Kostiakov infiltration model was fitted to land use infiltration curves, showing differences between land use and season. The values for fp oscillated between 53.6 and 548.8 mm hr^?1 and fc ranged from 105.3 to 1,061 mm. The order of the infiltration values goes as follows: agriculture > plantation > thornscrub > grassland. Land use changes in Vertisols induced modification of soil physical properties affecting processes like permeability, soil compaction and water availability.     

Carbon and nitrogen budgets of nematodes in arable soil

Summary The amounts of C and N that pass through the nematode biomass in four cropping systems, barley without and with N fertilization, grass ley and lucerne, has been estimated. The nematodes were sampled at the field site of a Swedish integrated research project Ecology of Arable Land: The Role of Organisms in Nitrogen Cycling. The nematode biomass was lower (200 mg dry weight m^–2) in the annual (barley) than in the perennial (grass and lucerne, 350 mg dry weight m^–2) crops. For respiration, the nematodes used 4–71 O₂m^–2 year^–1 corresponding to C liberation of 1.3%–2.0% of the carbon input to the soil. A higher relative contribution by bacterial-feeding nematodes to the C and N fluxes and a higher turnover rate of the nematode biomass is an indication of more rapid nutrient circulation in the annual than in the perennial cropping systems.     

Effect of post‐methanation effluent on soil physical properties under a soybean‐wheat system in a Vertisol

Post‐methanation effluent (PME) generated through bio‐methanation of distillery effluent, a foul‐smelling, dark colored by‐product of distillery industries, is applied to arable land in some areas near the vicinity of the distillery industries as an amendment. The PME contains considerable amount of organic matter and salt besides its high plant‐nutrient content. The present investigation was conducted for three years during 1999–2002 on soybean‐wheat cropping sequence to evaluate the effect of graded levels of post‐methanation effluent (PME) on soil physical properties and crop productivity in a deep Vertisol of central India. Six application doses of PME viz. S_2.5+W₀: 2.5 cm PME applied to soybean and wheat on residual nutrition, S_2.5+W_1.25: 2.5 cm PME to soybean and 1.25 cm to wheat, S_5.0+W₀: 5 cm PME to soybean and wheat on residual nutrition, S_5.0+W_2.5: 5.0 cm PME to soybean and 2.5 cm to wheat, S_10.0+W₀: 10 cm PME to soybean and wheat on residual nutrition, and S_10.0+W_5.0: 10.0 cm PME to soybean and 5.0 cm to wheat, were compared with 100% recommended NPK+FYM ? 4 Mg ha^–1 and control (no fertilizer, manure or PME). The application of PME increased the organic carbon content and electrical conductivity of the soil compared to control and 100% NPK+FYM treatment. The organic C content was maximum in S_10.0+W_5.0 (11.2 g kg^–1) and minimum in control (5.2 g kg^–1). Electrical conductivity increased from 0.47 dS m^–1 in control to 1.58 dS m^–1 in highest dose of PME (S_10.0+W_5.0). The PME treatments have not affected the soil pH. The application of PME showed a significant improvement in the physical properties of the soil. The mean weight diameter (MWD), percent water‐stable aggregation (% WSA), saturated hydraulic conductivity (K_sat), and water retention (WR) at 0.033 MPa suction were significantly (P < 0.05) more while bulk density (BD) and penetration resistance was significantly less in PME‐treated plots than that of control. The MWD showed a linear and positive relationship (r = 0.89**) with the soil organic C. Soybean recorded significantly higher seed yield at all PME treatments than control. Highest average soybean yield (2.39 Mg ha^–1) was recorded in S_10.0+W₀ but yield decreased significantly in S_10.0+W_5.0 (2.08 Mg ha^–1). In wheat, all the PME‐treated plots except S_2.5+W₀ yielded significantly higher than control while the 100% NPK+FYM treatment yielded (3.46 Mg ha^–1) at par with the S_10.0+W_5.0 (4.0 Mg ha^–1) and S_5.0+W_2.5 (3.66 Mg ha^–1). Fresh application of PME to wheat resulted in significant improvement in grain yield over that grown on residual fertility. Thus, application of PME to arable land, as an amendment, could be considered as a viable option for the safe disposal of this industrial waste.     

Transmission and storage properties of a tropical loamy sand soil as influenced by organic-based and inorganic fertilizers

Short-term effect of organic and inorganic amendments on soil physical quality (SPQ) is marked when dealing with tropical soils which are naturally exposed to a high risk of water erosion. This study assessed the suitability of Tithonia diversifolia (Mexican Sunflower) when incorporated as green manure (GM) and also composted with poultry manure (PM) and other organic-based and inorganic fertilizers to improve some hydraulic properties of an Alfisol subject to excessive drainage. Treatments applied include fresh T. diversifolia (GM), PM, T. diversifolia composted with PM, organo-mineral fertilizers (OMF), neem fertilizer (NF), inorganic fertilizer (20-10-10 NPK), and control in a randomized complete block design and replicated four times. Soil samples were collected at 0–20 cm depth to determine near steady-state infiltration rates (I_s), sorptivity, transmissivity, saturated hydraulic conductivity (K_s), macroporosity (MacP), microporosity (MicP), air capacity (AC), and relative water capacity (RWC). The I_s rates were significantly (P ≤ 0.05) reduced to optimum range with the addition of the organic fertilizers over very high value (128.7 cm hr^?1) observed for control. Whereas, K_s was enhanced in the order: GM > compost (CP) > NF > inorganic fertilizer > control > organo-mineral fertilizer > PM. Sorptivity and transmissivity were highest in control and inorganic fertilizer plots, indicating that the addition of organic fertilizers lowered these parameters while MacP, MicP, AC, and RWC were generally increased with the addition of organic-based and inorganic fertilizers. Specifically, NF increased MicP by 34% over control. Values for RWC which were within the optimum range (0.60–0.70) were only obtained with NF (0.74), OMF (0.72), NPK (0.70), and GM (0.60). The SPQ parameters assessed in this study were enhanced by the addition of fresh T. diversifolia applied as GM and CP compared to other treatments. Therefore, T. diversifolia usually burned by farmers should instead be incorporated into the soil as manure.     

Nutrient and carbon balances in organic vegetable production on an irrigated,sandy soil in northern Oman

Our understanding of nutrient and carbon (C) fluxes in irrigated organic cropping systems of subtropical regions is limited. Therefore, leaching of mineral nitrogen (N) and phosphorus (P), gaseous emissions of NH₃, N₂O, CO₂, and CH₄, and total matter balances were measured over 24 months comprising a total cropping period of 260 d in an organic‐cropping‐systems experiment near Sohar (Oman). The experiment on an irrigated sandy soil with four replications comprised two manure types (ORG1 and ORG2) characterized by respective C : N ratios of 19 and 25 and neutral detergent fiber (NDF)‐to‐soluble carbohydrates (SC) ratios of 17 and 108. A mineral‐fertilizer (MIN) treatment with equivalent levels of mineral N, P, and potassium (K) served as a control. The three treatments were factorially combined with a cropping sequence comprising radish (Raphanus sativus L.) followed by cauliflower (Brassica oleracea L. var. botrytis) or carrot (Daucus carota subsp. sativus). Over the 24‐months experimental period gaseous N emissions averaged 45 kg ha^–1 (59% NH₃‐N, 41%N₂O‐N) for MIN, 55 kg N ha^–1 (69% NH₃‐N, 31%N₂O‐N) for ORG1, and 49 kg N ha^–1 (59% NH₃‐N, 41% N₂O‐N) for ORG2. Carbon losses were 6.2 t ha^–1 (98% CO₂‐C, 2% CH₄‐C) for MIN, 9.7 t C ha^–1 (99% CO₂‐C, 1% CH₄‐C) for ORG1, and 10.6 t ha^–1 (98% CO₂‐C, 2% CH₄‐C) for ORG2. Exchange resin–based cumulative leaching of mineral N amounted to 30 kg ha^–1 for MIN, 10 kg ha^–1 for ORG1, and 56 kg ha^–1 for ORG2. Apparent surpluses of 361 kg N ha^–1 and 196 kg P ha^–1 for radish‐carrot and 299 kg N ha^–1 and 184 kg P ha^–1 for radish‐cauliflower were accompanied by K deficits of –59 kg ha^–1 and –73 kg ha^–1, respectively, for both cropping systems. Net C balances for MIN, ORG1, and ORG2 plots were –7.3, –3.1, and 1.5 t C ha^–1 for radish‐carrot and –5.0, 1.3, and 4.6 t C ha^–1 for radish‐cauliflower. The results underline the difficulty to maintain soil C levels in intensively cultivated, irrigated subtropical soils.     

Long-Term Cropping System, Tillage, and Poultry Litter Application Affect the Chemical Properties of an Alabama Ultisol

Sustainable agricultural practices have been steadily increasing in the last couple of decades. These management practices frequently involve cover crops, less or no-tillage, and organic fertilization. In this study, we evaluated the effects of cropping systems,tillage and no-tillage, and the application of poultry litter(PL) on selected soil physicochemical properties and soil test nutrients. Soil samples were collected from the topmost surface(0–5 cm) and subsurface(5–10 cm) layers. The general effect trend was PL application no-tillage cover crop cropping type. There were more statistically significant(P ≤ 0.05) correlations between the 18 soil attributes at the topmost surface than at the subsurface. This could be due to the accumulation of external C inputs and nutrients by crop residues and PL application as well as the retaining effects of no-tillage on less mobile nutrient components. Because of their high mobility and volatile nature, total nitrogen(N), ammonia-N(NH_4~+-N), and nitrate-N(NO_3~--N) levels varied greatly(high standard deviations), showing no consistent patterns among the treatments. Compared to the soybean cropping system, corn, especially with the wheat cover crop, contributed more to the total carbon(C) and sulfur(S) in the topmost surface soils(0–5 cm). Poultry litter application greatly increased pH, cation exchange capacity(CEC), base saturation, magnesium(Mg), phosphorus(P), calcium(Ca),sodium(Na), potassium(K), manganese(Mn), copper(Cu), and zinc(Zn) in both soil layers. Contrast comparisons revealed that PL application had more of an effect on these soil chemical properties than no-tillage and cropping systems. These results will shed light on developing better nutrient management practices while reducing their runoff potentials.