Soil erosion on Alfisols in Western Nigeria: II. Effects of mulch rates

The effects of four rates of straw mulching on runoff and soil loss were compared with those of no-tillage treatments under natural rainfall conditions using field runoff plots of 25 × 4 m established at 1, 5, 10 and 15% slopes on the International Institute of Tropical Agriculture (IITA) research site near Ibadan, Nigeria. The four rates of straw mulching were 0, 2, 4 and 6 t/ha. The mean annual runoff was 50, 10, 4 and 2% of the total annual rainfall for mulch rates of 0, 2, 4 and 6 t/ha, respectively. Runoff from unmulched treatments was not related to slope. Runoff loss from no-till treatments was only 2% of the rain received. The mean soil losses for the rainstorms greater than 25 mm were 143, 16, 2 and 0.4 kg/ha per mm of rain received for mulched rates of 0, 2, 4 and 6 t/ha, respectively. The soil loss declined exponentially with increasing mulch rate with exponents ranging from approximately ?0.3 to ?0.7. The soil losses from the no-till plots were equal to those from plots that received mulch at the rate of 6 t/ha. Soil erodibility was significantly influenced by time after clearing, with maximum K reached two to three years after forest removal. The nutrient loss in runoff and eroded soil was significant only for unmulched treatments. The maximum annual loss of NO₃-N in runoff was about 15 kg/ha. The maximum annual loss of total N in eroded soil from unmulched plots was about 180 kg/ha, that of P, 5 kg/ha, and that of K, about 14 kg/ha.     

Soil erosion on Alfisols in Western Nigeria: III. Effects of rainfall characteristics

The applicability of various erosivity indices was tested for runoff and soil loss from plowed bare-fallow field runoff plots of 25 × 4 m established on an Alfisol with natural slopes of 1, 5, 10 and 15%. The correlation coefficients of percent runoff from individual rainstorms with various indices such as kinetic energy (E), EI₃₀, KE > 1, rainfall amount (A), maximum intensity (I_m), and AI_m, were generally low. The correlation coefficients of all these indices with soil loss per storm were high and did not differ significantly from one another. The use of an empirical relation (kinetic energy = 916 + 331 log₁₀, I is in inches/h) may underestimate the kinetic energy of tropical rainstorms. The kinetic energy of tropical rainstorms may be significantly influenced by other factors such as wind velocity, drop size distribution and high rainfall intensity. The index AI_m has the advantage of simplicity of computation, and it incorporates one of the most important factors, peak intensity (I_m). Further improvements can be made in this index by incorporating a factor which accounts for the kinetic energy of a rainstorm. In the meantime, the index, AI_m, may be used to prepare an “iso-erodant” map, i.e. places with equal erosion potential. There also exists a linear correlation between rainfall amount per storm and AI_m. Such a relationship may be useful in estimating AI_m for regions where data from recording rain gauges are not available.     

Soil erosion on Alfisols in Western Nigeria: IV. Nutrient element losses in runoff and eroded sediments

Nutrient element losses in runoff and eroded sediments were monitored during 1972 on different slopes and under different soil and crop management treatments. The experiments were conducted on 25 × 4 m field runoff plots, established on natural slopes of 1, 5, 10 and 15%. The soil and crop management treatments consisted of bare fallow (plowed), maize-maize (plowed and mulched), maize-maize (plowed), maize-cowpeas (no-till), and cowpeas-maize (plowed).Total loss of nutrient elements in runoff and eroded soil materials was significantly affected by slope and by soil and crop management treatments. Total annual nutrient element losses in runoff were 55 kg/ha for bare-fallow, 17 kg/ha for maize-maize (plowed), 12 kg/ha for cowpeas-maize (plowed), 2.3 kg/ha for maize-maize (plowed and mulched) and 4.3 kg/ha for maize-cowpeas (no-till). The concentration of nitrate in seepage water was two or three times higher than in surface water. Nutrient losses in eroded soil materials from the mulched and no-till treatments were negligible. From the plowed treatments, greatest losses were of organic matter and total nitrogen. The enrichment ratios were 2.4 times for organic carbon, 1.6 times for N, and 5.8 times for available phosphorus.     

Soil degradative effects of slope length and tillage methods on alfisols in Western Nigeria. I. Runoff,erosion and crop response

Field runoff plots were established in 1984 to evaluate the effects of slope length on runoff, soil erosion and crop yields on newly cleared land for four consecutive years (1984–1987) on an Alfisol at Ibadan, Nigeria. The experimental treatments involved six slope lengths (60 m to 10 m at 10-m increments) and two tillage methods (plough-based conventional tillage and a herbicide-based no-till method) of seedbed preparation. A uniform crop rotation of maize (Zea mays)/cowpeas (Vigna unguiculata) was adopted for all four years. An uncropped and ploughed plot of 25 m length was used as a control. The water runoff from the conventional tillage treatment was not significantly affected by slope length, but runoff from the no-till treatment significantly increased with a decrease in slope length. The average runoff from the no-till treatment was 1·85 per cent of rainfall for 60 m, 2·25 per cent for 40 m, 2·95 per cent for 30 m, 4·7 per cent for 20 m and 5·15 per cent for 10 m slope length. In contrast to runoff, soil erosion in the conventional tillage treatment decreased significantly with a decrease in slope length. For conventional tillage, the average soil erosion was 9·59 Mg ha⁻¹ for 60 m, 9·88 Mg ha⁻¹ for 50 m, 6·84 Mg ha⁻¹ for 40 m, 5·69 Mg ha⁻¹ for 30 m, 1·27 Mg ha⁻¹ for 20 m and 2·19 Mg ha⁻¹ for 10 m slope length. Because the no-till method was extremely effective in reducing soil erosion, there were no definite trends in erosion with regard to slope length. The average sediment load (erosion:runoff ratio) also decreased with a decrease in slope length from 66·3 kg ha⁻¹ mm⁻¹ for 60 m to 36·3 kg ha⁻¹ mm⁻¹ for 10 m slope length. The mean C factor (ratio of soil erosion from cropped land to uncropped control) also decreased with a decrease in slope length. Similarly, the erosion:crop yield ratio decreased with a decrease in slope length, and the relative decrease was more drastic in conventional tillage than in the no-till treatment. The slope length (L) and erosion relationship fits a polynomial function (Y=c+aL+bL²). Formulae are proposed for computing the optimum terrace spacing in relation to slope gradient and tillage method. © 1997 John Wiley & Sons, Ltd.     

Soil erosion on alfisols in Western Nigeria: I. Effects of slope,crop rotation and residue management

The effect of slope, crop rotation and residue management on runoff and soil loss was investigated using field runoff plots of 25 m × 4 m on natural slopes of 1, 5, 10 and 15% on an Alfisol on the International Institute of Tropical Agriculture (IITA) research site near Ibadan, Nigeria. The soil and crop management treatments consisted of conventionnally plowed bare fallow, maize-maize (conventionally plowed and mulched), maize-maize (conventionally plowed), maize-cowpeas (zero-tillage), and cowpeas-maize (conventionally plowed). The effect of two contour lengths of 12.5 and 37.5 m was also investigated for the maize-cowpeas rotation.Soil erosion under slopes of 5, 10 and 15% is severe for these soils and if not controlled can limit crop growth.Mulching and no-till treatments had negligible runoff and soil loss. During 1973 the annual runoff losses from the 15% slope were 36, 2 and 2% of the total annual rainfall for the bare-fallow, mulched and no-till treatments, respectively. Annual soil losses during 1973 from the 15% slope were 230 t/ha from bare-fallow, 0.0 t/ha from maize-maize (mulched), 41 t/ha from maize-maize (conventional plowing), 0.1 t/ha from maize-cowpeas (no-till) and 43 t/ha from cowpeas-maize (plowed). Significant soil erosion was associated with only a few extremely intense storms. The soil loss during a single rainstorm increased exponentially with an increase in slope gradient. There was no definite relationship between contour length and runoff or soil loss.     

Soil management for Alfisols in the semiarid tropics: erosion, enrichment ratios and runoff

Abstract. Continuous cultivation of soils of the semiarid tropics has led to significant land degradation. Soil erosion and nutrient loss caused by high runoff volumes have reduced crop yields and contributed to offsite damage. We compared a number of soil management practices (tillage, mulch and perennial/annual rotational based systems) for their potential to improve crop production and land resource protection in an Alfisol of the semiarid tropics of India. Runoff and soil erosion were monitored and surface soil and sediment were analysed for nitrogen and carbon to determine enrichment ratios. Amelioration of soils with organic additions (farmyard manure, rice straw) or rotating perennial pasture with annual crops increased soil carbon and nitrogen contents and reduced runoff, soil erosion and nutrient loss. Soil erosion totalled less than 7 t ha^–1, but enrichment ratios were often greater than 2 resulting in up to 27 kg N ha^–1 and 178 kg C ha^–1 being lost in sediment. Up to an extra 250 mm of water per year infiltrated the soil with organic additions and was available for crop water use or percolation to groundwater. The results show that there are good opportunities for reducing degradation and increasing productivity on farms.     

Soil erosion and changes in the physical properties of Lithuanian Eutric Albeluvisols under different land use systems

Abstract

The investigations aimed to: 1) evaluate water erosion rates on undulating slopes in Lithuania under different land use systems; 2) study changes in soil physical properties on the differently eroded slopes; and 3) better understand relationships between soil physical properties and soil erodibility. Research data were obtained on loamy sand and clay loam Eutric Albeluvisols located on the undulating hilly relief of the ?emai?iai Uplands of Western Lithuania. The results of 18 years of water erosion investigations under different land use systems on slopes of varying steepness are presented. Attention is focused on changes in soil physical properties in relation to soil erosion severity. Measured water erosion rates in the field experiments were: 3.2–8.6 m³ ha^?1 yr^?1 under winter rye, 9.0–27.1 m³ ha^?1 yr^?1 under spring barley and 24.2–87.1 m³ ha^?1 yr^?1 under potatoes. Perennial grasses completely prevented water erosion, while erosion-preventive grass-grain crop rotations (67% grasses, 33% cereal grains) decreased soil losses by 75–80% compared to the field crop rotation, containing 17% tillage crops (potatoes), 33% grasses and 50% cereal grains. The grain-grass crop rotation (33% grasses and 67% cereal grains) decreased soil erosion rates by 23–24%. The percentage of clay-silt and clay fractions of arable soil horizons increased, while the total soil porosity and moisture retention capacity decreased with increased soil erosion. Phytocenoses, including sod-forming perennial grasses and grass-grain crop rotations, led to changes in the physical properties of eroded soils; soil bulk density decreased and percentage total porosity and moisture retention capacity increased. The grass-grain crop rotations increased the water-stable soil structure (measured as water-stable soil aggregates) by 11.03 per cent units and sod-forming perennial grasses increased aggregate stability by 9.86 per cent units compared with the grain-grass crop rotation on the 10–14° slope. Therefore, grass-grain crop rotations and sod-forming perennial grasses decreased soil erodibility and thus could assist both erosion control and the ecological stability of the vulnerable hilly-undulating landscape.     

Soil physical and hydrological properties under three biofuel crops in Ohio

Abstract

While biofuel crops are widely studied and compared for their energy and carbon footprints, less is known about their effects on other soil properties, particularly hydrologic characteristics. Soils under three biofuel crops, corn (Zea mays), switchgrass (Panicum virgatum), and willow (Salix spp.), were analyzed seven years after establishment to assess the effects on soil bulk density (ρ_b), penetration resistance (PR), water-holding capacity, and infiltration characteristics. The PR was the highest under corn, along with the lowest associated water content, while PR was 50–60% lower under switchgrass. In accordance with PR data, surface (0–10 cm) bulk density also tended to be lower under switchgrass. Both water infiltration rates and cumulative infiltration amounts varied widely among and within the three crops. Because the Philip model did not fit the data, results were analyzed using the Kostiakov model instead. Switchgrass plots had an average cumulative infiltration of 69 cm over 3 hours with a constant infiltration rate of 0.28 cm min^?1, compared with 37 cm and 0.11 cm min^?1 for corn, and 26 cm and 0.06 cm min^?1 for willow, respectively. Results suggest that significant changes in soil physical and hydrologic properties may require more time to develop. Soils under switchgrass may have lower surface bulk density, higher field water capacity, and a more rapid water infiltration rate than those under corn or willow.     

Soil degradative effects of slope length and tillage methods on alfisols in western Nigeria. III.Soil physical properties

Effects of six slope lengths, 60 m to 10 m with 10-m increments, on soil physical properties were evaluated for plough-based conventional till and no-till seedbed preparation on field runoff plots for three consecutive years from 1984 to 1987. Soil physical properties measured included texture, bulk density, infiltration capacity, and soil moisture retention characteristics. Conventional till treatment caused a rapid increase in soil bulk density and penetration resistance, and decrease in available water capacity and equilibrium infiltration rate. Gravel content increased with cultivation duration. Soil bulk density of 0–5 cm depth was 1·20 Mg m⁻³ for 1984, 1·39 Mg m⁻³ for 1985 and 1·46 Mg m⁻³ for 1986 for conventional till; and 1·13 Mg m⁻³ for 1984, 1·33 Mg m⁻³ for 1985, and 1·27 Mg m⁻³ for 1986 for the no-till treatment. The penetration resistance of the no-till treatment was relatively low and increased with cultivation duration. Mean penetration resistance for 0–5 cm depth was 2·2 kg cm⁻² in 1984, 2·71 kg cm⁻² in 1985, and 3·79 kg cm⁻² in 1986. The available water capacity decreased in both tillage methods without any consistent trends with regard to slope length. The equilibrium infiltration rate declined drastically for long slopes and conventional till methods. The data support the conclusion that these soils should be managed with short slope lengths and a no-till method of seedbed preparation. © 1997 John Wiley & Sons, Ltd.     

The Role of Soil Mineralogical Characteristics in Sustainable Soil Fertility Management: A Case Study of Some Tropical Alfisols in Nigeria

The pedogenic horizons of nine profile pits dug across three toposequences were studied to determine the soil mineralogical characteristics and its implications on sustainable management of the fertility of some tropical Alfisols in Nigeria. Results showed that the epipedon which were predominantly ochric had textures that ranged from sand to sandy loam, while the subsurface (B/Bt) horizons had sandy clay loam to sandy clay texture and were gravelly (31.79–83.04%). The soil reaction ranged from strongly acid to neutral (pH 5.10 to 7.05). Calcium and magnesium dominated the exchange sites and accounted for about 75% of the exchangeable bases. Illite/mica and kaolinite were the dominant minerals in the clay fractions, while quartz, mica, and feldspars dominated the fine sand and silt fractions of the soils. While the presence of illite and mica could be important for potassium nutrition in these soils, kaolinite and oxides of iron could also cause phosphorus fixation.     

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 slope length on erosion of some alfisols in Western Nigeria

Erosion was monitored for erosive rainstorms received during 1977 and 1978 from an Alfisol at Ibadan in western Nigeria on bare plowed soil using field runoff plots on natural slopes of 1, 5, 10 and 15% and with 5, 10, 15 and 20 m slope lengths. Equations of the type A = αL^b were computed relating soil erosion (A) to slope length (L).Erosion was affected more by slope gradient than by slope length and was in the order of 1, 17.6, 31.3 and 22.8 for 1977 and 1, 25.5, 53.0 and 62.4 for 1978 for 5, 10 and 15% slope gradients, respectively. For gentle slope gradients of 1 and 5%, slope length had little effect on erosion. During 1978, erosion for 10% slopes was in the order of 1, 1.05, and 1.08 for 5, 10 and 15 m slope lengths, respectively. For 15% slope, however, the soil erosion was in the order of 1, 1.11, 1.51 and 1.60 for 5, 10, 15 and 20 m slope lengths. The mean sediment concentration (averaged over all slope gradients), was 1, 1.27, 1.50, 1.99 for 1977 and 1, 1.61, 2.71, 2.73 for 1978 for 5, 10, 15 and 20 m slope lengths, respectively.     

Soil physical and chemical changes due to tillage and their implications for erosion and productivity

A seven-year tillage trial was conducted in central New South Wales, Australia to measure the effect and extent of conservation tillage practices on soil physical and chemical properties. Three tillage treatments, traditional tillage (TT), reduced tillage (RT) and direct drilling (DD) were imposed on hardsetting red-brown earths at Cowra and Grenfell. A fourth treatment, direct drilling without grazing (NT) was imposed at Cowra only.

At Cowra there was a significant trend of reduced total runoff in the DD and NT treatments but not in the RT treatment. Runoff significantly increased in the TT treatment.

At Grenfell, runoff decreased in all treatments but only significantly in the DD and RT treatments. Similar trends in total sediment loss were measured at both sites.

Associated physical measurements of saturated hydraulic conductivity, sorptivity and bulk density confirmed that the changes in runoff were due to the creation of macroporosity greater than 0.75 mm diameter. The relationship between macroporosity, organic carbon and aggregate stability is discussed. Conclusions were that in these soil types runoff and sediment loss were affected more by destruction of macroporosity due to cultivation than changes in organic carbon from residue retention. To achieve these soil improvements using conservation tillage a continuous cropping period of four years was necessary to obtain significant and consistent trends.

Soil chemical data showed that total nitrogen increased with conservation tillage practices. Available phosphorus changes due to tillage were not observed because of more than adequate fertiliser applied. Soil pH decreased significantly in the DD and NT treatments at Cowra only. The implications of these chemical changes are discussed.     

Deforestation and land-use effects on soil degradation and rehabilitation in western Nigeria. II. Soil chemical properties

Temporal changes in soil chemical and nutritional properties were evaluated in a long-term experiment conducted on Alfisols in West Africa. Effects of land use and cropping duration on soil chemical properties at 0–5 cm and 5–10 cm depths were evaluated for five treatments: (1) alley cropping with Leucaena leucocephala established on the contour at 4-m intervals; (2) mucuna (Mucuna utilis) fallowing for 1 year followed by maize (Zea mays)-cowpea (Vigna unguiculata) cultivation for 2 years on severely degraded land; (3) fallowing with mucuna on moderately degraded soils; (4) ley farming involving growing improved pastures for 1 year, grazing for the second year, and growing maize-cowpea for the third year on severely degraded land; (5) ley farming on moderately degraded soils. Soil chemical properties were measured once every year from 1982 through 1986 during the dry season, and included pH, soil organic carbon (SOC), total soil nitrogen (TSN), Bray-P, exchangeable cations, and effective cation exchange capacity (CEC). Regardless of the cropping system treatments, soil chemical quality decreased with cultivation time. The rate of decrease at 0–5 cm depth was 0·23 units year⁻¹ for pH, 0·05 per cent year⁻¹ for SOC, 0·012 per cent year⁻¹ for TSN, 0·49 cmol kg⁻¹ year⁻¹ for Ca²⁺, 0·03 cmol kg⁻¹ year⁻¹ for Mg²⁺, 0·018 cmol kg⁻¹ year⁻¹ for K⁺, and 0·48 cmol kg⁻¹ year⁻¹ for CEC. Although there was also a general decrease in soil chemical quality at 5–10 cm depth, the trends were not clearly defined. In contrast to the decrease in soil properties given above, there was an increase in concentration at 0–5 cm depth of total acidity with cultivation time at the rate of 0·62 cmol kg⁻¹ year⁻¹, and of Mn³⁺ concentration at the rate of 0·081 cmol kg⁻¹ year⁻¹. Continuous cropping also increased the concentration of Bray-P at 0–5 cm depth due to application of phosphatic fertilizer. Trends in soil chemical properties were not clearly defined with regards to cropping system treatments. In general, however, soil chemical properties were relatively favorable in ley farming and mucuna fallowing treatments imposed on moderately degraded soils. Results are discussed in terms of recommended rates of fertilizer use, in view of soil test values, expected yields, and critical limits of soil properties.     

Soil management options for Alfisols in the semi-arid tropics: annual and perennial crop production

A field experiment was conducted in the semi arid tropics to study the effects of soil structural modification on cropping systems. The aim was to improve crop production and land resource protection using innovative soil management practices. Tillage, mulch and perennial/annual rotational based systems were compared for 5 years in an Alfisol at ICRISAT in India. Crop yield parameters, including grain and biomass yield, leaf area index, crop cover, and plant height were measured. Results indicate significant benefits to annual crop yield (maize, sorghum) from improved water supply due to mulching with farmyard manure or and rice straw, and due to rotation with prior-perennial crops. Grain yields were 16 to 59% higher in mulched treatments compared to unmulched treatments, with similar increases for fodder yields. Annual crop yields after 4 years of perennials were 14 to 81% higher than unmulched treatments, except for low fertility maize grown after buffel grass. The interaction with chemical fertility was less clear than for water supply. The results have implications for soil management throughout the semi-arid tropics.     

The effects of different management practices on the physical properties of a sandy loam soil in Southern Nigeria

The effects of different management practices on the physical properties of a sandy loam soil in Southern Nigeria were studied for two cropping seasons. The bulk densities of the top 0–10-cm soil depths were significantly reduced in plots under 13 years of Panicum maximum and Centrosema pubescens covers. Pores of equivalent cylindrical diameter > 0.05 mm were increased significantly under the two covers. Up to 33% of the saturation water content was released between tensions of 0 and 0.06 bar in the sandy loam soil of all the treatment plots. Furthermore an average of 24% of this water was released between tensions of 0.06 and 0.33 bar. Infiltration rates, measured at the end of the growing season, ranged from 240 mm h⁻¹ under the bare fallow treatment to 1326 mm h⁻¹ under the Centrosema cover. There was no significant difference between the tilled and no-tillage plots. Saturated hydraulic conductivities were significantly higher under the Panicum and Centrosema covers. The effect of tillage on conductivity was not appreciable. The highest weekly 5-cm depth, 1.30 p.m. soil temperature (32°C) was obtained under the bare fallow treatment and the lowest (23.5°) under the Panicum cover. Tillage had no significant effect on the soil temperature. Thirteen years of continuous Centrosema and Panicum covers had a significant effect on the physical properties of the tropical sandy loam soil. Tillage effects were not significant after 2 years of cropping.     

基于GIS/RS和USLE鄱阳湖流域土壤侵蚀变化

将空间信息技术（RS和GIS）和通用土壤流失方程（USLE）相结合对鄱阳湖流域土壤侵蚀量进行计算。分别利用1990年和2000年TM/ETM+影像分类得到两期土地利用/覆盖类型图,结合鄱阳湖流域数字高程模型（DEM）、土壤类型分布图和流域降雨资料分别获取USLE模型中各因子值的空间分布,最后计算流域2个年份的土壤侵蚀空间分布图。研究表明：鄱阳湖流域土壤侵蚀区域主要分布在赣江上游,信江上游,抚河上中游和修水上游地区;鄱阳湖流域1990年和2000年大范围土地经受着Ⅰ级微度与Ⅱ级轻度侵蚀,其侵蚀面积之和分别占流域面积的97.38%和97.30%;而流域产沙主要来源于Ⅱ级轻度侵蚀和Ⅲ级中度侵蚀,所占土壤侵蚀总量分别为58.16%和51.20%,其中中度以上等级的侵蚀对产沙量的贡献是不可忽视的;从1990年到2000年土壤侵蚀等级变化呈现了由中等级侵蚀（Ⅱ级轻度侵蚀和Ⅲ级中度侵蚀）向低等级（Ⅰ级微度侵蚀）和高等级侵蚀（Ⅴ级极强度和Ⅵ级剧烈侵蚀）的2个极端演化的趋势。鄱阳湖流域土壤侵蚀量从1990年到2000年增长幅度达6.3%;土壤平均侵蚀模数都约为1 100 t/(km2·a),属于Ⅱ级轻度侵蚀。分析2个年份的土地利用/覆盖变化,发现鄱阳湖流域湿地和农田面积减少,建筑用地增加均是造成土壤侵蚀量增加的因素,而降雨侵蚀力因子空间格局也对土壤侵蚀空间分布具有重要影响,最后提出了鄱阳湖流域水土保持规划措施。     

Soil hydraulic and physico-chemical properties of Ultisols and Inceptisols in south-eastern Nigeria

Understanding soil water dynamics and storage is important to avoid crop failure on highly weathered, porous and leached soils. The aim of the study was to relate soil moisture characteristics to particle-size distributions and chemical properties. On average, Atterberg limits were below 25% in the A-horizon and not more than26.56% in the B-horizon, whereas soil bulk density was between 1.27 and 1.66Mgm^?3. The saturated hydraulic conductivity (K_sat) was generally between 0.20 and 5.43 cm h^?1 in the top soil and <1.31 cm h^?1 in the subsoil. The higher K_sat values for the A-horizons were attributed to the influence soil microorganisms operating more in that horizon. The amount of water retained at field capacity or at permanent wilting point was greater in the B-horizons than in the A-horizons, suggesting that clay accumulation in the B-horizon and evapotranspiration effects in the A-horizon may have influenced water retention in the soils. Soil moisture parameters were positively related to clay content, silt content, exchangeable Mg²⁺, Fe₂O₃ and Al₂O₃, and negatively related to sand content, SiO₂, sodium absorption ratio, exchangeable sodium percentage and bulk density. The low clay content may explain why drainage was so rapid in the soils.     

Influence of Soil and Fertilizer Nutrients on Sustainability of Rainfed Finger Millet Yield and Soil Fertility in Semi-arid Alfisols

Productivity of rainfed finger millet in semiarid tropical Alfisols is predominantly constrained by erratic rainfall, limited soil moisture, low soil fertility, and less fertilizer use by the poor farmers. In order to identify the efficient nutrient use treatment for ensuring higher yield, higher sustainability, and improved soil fertility, long term field experiments were conducted during 1984 to 2008 in a permanent site under rainfed semi-arid tropical Alfisol at Bangalore in Southern India. The experiment had two blocks—Farm Yard Manure (FYM) and Maize Residue (MR) with 5 fertilizer treatments, namely: control, FYM at 10 t ha^?1, FYM at 10 t ha^?1 + 50% NPK [nitrogen (N), phosphorus (P), potassium (K)], FYM at 10 t ha^?1 + 100% NPK (50 kg N + 50 kg P + 25 kg K ha^?1) and 100% NPK in FYM block; and control, MR at 5 t ha^?1, MR at 5 t ha^?1 + 50% NPK, MR at 5 t ha^?1 + 100% NPK and 100% NPK in MR block. The treatments differed significantly from each other at p < 0.01 level of probability in influencing finger millet grain yield, soil N, P, and K in different years. Application of FYM at 10 t ha^?1 + 100% NPK gave a significantly higher yield ranging from 1821 to 4552 kg ha^?1 with a mean of 3167 kg ha^?1 and variation of 22.7%, while application of maize residue at 5 t ha^?1 + 100% NPK gave a yield of 593 to 4591 kg ha^?1 with a mean of 2518 kg ha^?1 and variation of 39.3% over years. In FYM block, FYM at 10 t ha^?1 + 100% NPK gave a significantly higher organic carbon (0.45%), available N (204 kg ha^?1), available P (68.6 kg ha^?1), and available K (107 kg ha^?1) over years. In maize residue block, application of MR at 5 t ha^?1 + 100% NPK gave a significantly higher organic carbon (0.39%), available soil N (190 kg ha^?1), available soil P (47.5 kg ha^?1), and available soil K (86 kg ha^?1). The regression model (1) of yield as a function of seasonal rainfall, organic carbon, and soil P and K nutrients gave a predictability in the range of 0.19 under FYM at 10 t ha^?1 to 0.51 under 100% NPK in FYM block compared to 0.30 under 100% NPK to 0.67 under MR at 5 t ha^?1 application in MR block. The regression model (2) of yield as a function of seasonal rainfall, soil N, P, and K nutrients gave a predictability in the range of 0.11 under FYM at 10 t ha^?1 to 0.52 under 100% NPK in FYM block compared to 0.18 under MR at 5 t ha^?1 + 50% NPK to 0.60 under MR at 5 t ha^?1 application in MR block. An assessment of yield sustainability under different crop seasonal rainfall situations indicated that FYM at 10 t ha^?1 + 100% NPK was efficient in FYM block with a maximum Sustainability Yield Index (SYI) of 41.4% in <500 mm, 64.7% in 500–750 mm, 60.2% in 750–1000 mm and 60.4% in 1000–1250 mm rainfall, while MR at 5 t ha^?1 + 100% NPK was efficient with SYI of 29.6% in <500 mm, 50.2% in 500–750 mm, 40.6% in 750–1000 mm, and 39.7% in 1000–1250 mm rainfall in semi-arid Alfisols. Thus, the results obtained from these long term studies incurring huge expenditure provide very good conjunctive nutrient use options with good conformity for different rainfall situations of rainfed semiarid tropical Alfisol soils for ensuring higher finger millet yield, maintaining higher SYI, and maintaining improved soil fertility.