Heterogeneity In Soil Fertility Research Articles

Linking topography, soil variability, and early successional vegetation in abandoned gold mines in the tropical rainforest of Colombia's Chocó Biogeographic region

Soil fertility heterogeneity is one of the main factors affecting early recovery and plant succession toward a target plant community. This study examined the influence of topography on the diversity and composition of plant communities established in areas degraded by opencast mining in Chocó, Colombia. Soil fertility and plant community were characterized in the four topographic formations identified in the abandoned mines: plains (PL), slopes (SLP), floodplains (FP), and sand and gravel mounds (SGM). Topographic formations did not result in significant differences in soil properties. However, a gradient of fertility and vegetation cover was observed: from the SGM, with less fertile soils and little vegetation, to the PL, SLP, and FP, with the most fertile soils and greater vegetation cover and density. The species composition found in PL, SLP, and FP was similar but differed from that of SGM. These results suggest that the SGM does not promote early revegetation in the mines. However, experimental studies are necessary to determine how topographic formations and soil conditions resulting from mining should be managed to facilitate the early recovery of vegetation and the ecological restoration of areas affected by mining.

Using Yield Mapping Data to Identify Areas of In-field Heterogeneity in Soil Fertility

Mathematical models developed on the basis of a big data array of stationary agrochemical field experiments of the Federal State Budgetary Scientific Institution "Federal Research Center "Nemchinovka" on different types (subtypes) of soils for calculating the potential yield and doses of fertilizers for the planned crop yield are presented. The combined use of such models with yield mapping data can potentially be used to identify areas of in-field heterogeneity in soil fertility.

High fire frequency reduces soil fertility underneath woody plant canopies of Mediterranean ecosystems

Spatial heterogeneity of soil properties plays a major role in regulating ecosystem structure and functioning. In general, soil resources accumulate beneath woody plant-covered patches more than in the open interspace, making them function as fertility islands. Whilst wildfire is a common disturbance, little information is available on the role of particular plant species in maintaining soil fertility underneath in areas that are subjected to recurrent fires. This is an important issue given that land abandonment, together with a warmer and drier climate, is increasing fire danger in regions such as the Mediterranean. We determined whether increasing fire frequency, producing changes from a Quercus ilex L., woodland to a shrubland, modifies the effect of woody plant canopy on soil fertility. Additionally, the effect of fire history on species-specific leaf and litter nutrient concentration was assessed. Areas affected by none, one, two or three fires were selected. Within each area, soil fertility was measured underneath Cistus ladanifer L., Retama sphaerocarpa L., Phillyrea angustifolia L. and Quercus ilex canopies and in open interspace. Unburned soils located underneath P. angustifolia and Q. ilex canopies were significantly more fertile than in open interspaces. The microsite effect on soil fertility was fire frequency dependent. As fire frequency increased, the plant canopy microsite effect decreased for soil organic matter (SOM), cation exchange capacity (CEC), total C, P, Ca, K and Mg, labile phosphate, arylsulfatase and acid phosphatase activities. Total N, ammonium, nitrate and β-glucosidase activity decreased with increasing fire frequency, but their spatial variability was maintained along all fire frequency scenarios. Fire frequency decreased foliar N concentration but increased P concentration in some species, leading to a decrease in their N:P ratio. Our findings suggest that soil fertility heterogeneity will be reduced with increasing fire frequency. This could compromise the recovery of soil and ecosystem functioning.

Explaining Soil Fertility Heterogeneity in Smallholder Farms of Southern Ethiopia

Soil is spatially heterogeneous and needs site-specific management. However, soil nutrient information at larger scale in most cases is lacking. Consequently, fertilizer advisory services become dependent upon blanket recommendation approach. Subsequently, it affects yield and profitability. This study is aimed at explaining soil fertility heterogeneity in Wolaita zone, Southern Ethiopia. About 789 soil samples were collected to evaluate soil physical (color, particle size, and bulk density) and chemical properties (pH, OC, N, P, K, Ca, Mg, B, Cu, Fe, Mn, Zn, PBS, and CEC). The laser diffraction method for soil particles and mid-infrared diffused reflectance (MIR) spectral analysis for OC, TN, and CEC determination were employed. Mehlich-III extraction and inductively coupled plasma (ICP) spectrometer measurement were used for the remaining elements. The result based on principal component analysis showed that 52% of the total variations were explained by exchangeable bases, CEC, pH, available P, Cu, B, and particle sizes. Clay texture and acidic soil reaction are dominant. Soil parameters with the following ranges were found at low status: soil OC (0.2–6.9%), total N (0.01–0.7%), available P (0.1–238 mg/kg), S (4–30 mg/kg), B (0.01–6.9 mg/kg), and Cu (0.01–5.0 mg/kg). Besides, low levels of exchangeable Ca, Mg, and K (Mg-induced K deficiency) on 22, 34, and 54% soil samples, respectively, were recorded. The soil contained sufficient Fe, Zn, and Mn. In conclusion, the study aids in developing practical decision for optimum soil management interventions and overcomes lower productivity occurring due to fertilizer use that is not tailored to the local conditions. Overall, continuous cropping, low return of crop residues, and low and/or no fertilizer application might have caused the low status of N, P, K, S, B, and Cu. Therefore, application of inorganic fertilizers specific to the site, lime in acidic soils, and organic fertilizers are recommended to restore the soil fertility and improve crop productivity.

Efficiency of barley foliar feeding under conditions of leached chernozem fertility heterogeneity

The article presents the results of studies conducted on the effectiveness of barley foliar feeding under field experiment conditions. The studies were carried out in a field stationary experiment in a grain-vapor-tilled crop rotation system with the following rotation: green-manured fallow - spring wheat - barley - maize - spring wheat. The object of the research was leached chernozem. Rotation cropping was sown on two degrees of ground fertilization – without fertilizer and with fertilizer. Urea (carbamide) was added as barley foliar feeding. Spring wheat that was sown on rape plant green-manured fallow served as the forecrop to the barley. Soil fertility heterogeneity was determined by examining barley crops during the tillering period (biomass scanning). Unmanned aerial vehicles manufactured by Krasaeroskan were used for this purpose. The results of NDVI index determination in the field experiment formed the basis for determining the mineral nitrogen fertilizer doses. Such doses were refined by tissue diagnostics. It was established that foliar feeding with mineral nitrogen fertilizers (urea) contributed to an increase in barley productivity.

Soil fertility gradients shape the agrobiodiversity of Amazonian homegardens

The importance of homegardens for the conservation of agrobiodiversity, the maintenance of farm ecosystem processes, and the economic and food security of rural populations worldwide is increasingly recognized. While biophysical and socio-economic conditions are considered to influence homegarden management, and affect their ecological and societal relevance, little is known about how variation in soil properties affects these agroecosystems. By combining soil data with extensive botanical inventories, we investigated how farmers’ use and management of soil variation results in differences in the structure, diversity and the floristic composition of homegardens in Central Amazonia. We sampled 70 homegardens located along the gradient from low-fertility Ferralsols to Amazonian Dark Earths (ADE), i.e., fertile anthropogenic soils created by pre-Columbian populations at least 500 years ago. Our results show that several characteristics of homegardens are significantly influenced by variation in soil texture and fertility. While differences in soil texture are due to natural soil variation, observed heterogeneity in soil fertility was largely the result of pre-Columbian and modern soil transformations. Homegardens on sandier soils tended to be more diverse in plant species and to have more individual plants; homegardens on more fertile soils tended to have fewer trees and palms, more herbs, shrubs and climbers, and a higher total number of species and landraces; variation in soil fertility was significantly related to differences in the composition of species and landraces. Our results show that farmers’ use of natural and anthropogenic variation in soil properties influences agrobiodiversity patterns in homegardens. Pre-Columbian and modern soil enrichment increases soil heterogeneity in the landscape, resulting in strong soil fertility gradients that shape the agrobiodiversity of current Amazonian homegardens.

Nutrient Management Strategies on Heterogeneously Fertile Granitic‐Derived Soils in Subhumid Zimbabwe

Maize (Zea mays L.) is the staple food in southern Africa, but low soil fertility and lack of effective fertilization strategies for variable soil conditions hamper efficient use of nutrient resources. The objective of this study was to establish the influence of soil fertility heterogeneity on maize yield response to manure, liming, and inorganic fertilizers. Three sites, selected to represent three soil fertility domains based on soil organic carbon (SOC) between 3.5 to 8.9 g SOC kg−1 soil, were used during two cropping seasons. Nitrogen, P, K, and S were applied alone (NPKS) or in combinations involving lime, cattle manure, and micronutrients. Grain and stover were analyzed for nutrient uptake, and agronomic efficiencies were computed for N and P. Across sites, maize grain yields increased with increasing SOC. In Year 2, lime was the most important component for increasing maize yields in low SOC soil. For the medium and high SOC soils, treatments with NPKS + manure resulted in the best efficiencies. Although soil pH was low in these fields as well, lime which was applied only in Year 1, did not improve yields either year. Maize yields and nutrient uptake were strongly affected by SOC content, with yields for a site with 3.5 g SOC kg−1 soil significantly lower than the two sites that had >5.3 g SOC kg−1soil. We conclude that farmers must strategically target their limited nutrients resources to fields that are not yet degraded and maintain soil fertility to guarantee returns to fertilizer investments.

Soil organic fractions in cultivated and uncultivated Ferralsols in Uganda

Ferralsols are chemically poor soils, with management challenges associated with soil fertility heterogeneity and nitrogen limitations. Proper assessment of soil organic matter fractions can be instrumental in understanding the causes of limited nitrogen supply, and thus addressing soil fertility heterogeneity. A study was conducted in cultivated and uncultivated Ferralsols, in order to assay soil organic carbon (SOC), its particle-size fractions and their influence on soil fertility heterogeneity across small farms in central Uganda. Soil samples were taken from the 0–15 and 15–30cm depths from 30 cultivated fields classified as of low fertility, medium fertility and high fertility, and from two nearby sites in a native shrubland as references. Soil samples were physically fractionated into sand (2000–63μm), silt (63–2μm) and clay (<2μm). Total SOC and N were analyzed in bulk samples and each size fraction, and the Carbon Management Index (CMI), a widely used indicator of soil quality, was calculated for each field. The CMI in cultivated soils was far below the 100% in reference soils, reaching 34.7, 40.3 and 87% in low, medium and high fertility fields, respectively. SOC and N concentrations decreased in particle-size separates in the order clay>silt>sand. The SOC pool and N in the clay-sized fraction were correlated to soil fertility indicators. More N was stored in the silt+clay size fractions, a generally more stable pool, than in the more labile sand-sized pool. The SOC pool in sand size fractions was far below in low and medium fertility soils than in a reference uncultivated soil. Thus, the sand-sized pool emerged as the most likely cause of limited N supply in cultivated low-input Ferralsols in Uganda.

Benefits of legume–maize rotations: Assessing the impact of diversity on the productivity of smallholders in Western Kenya

Agricultural intensification of farming systems in sub-Saharan Africa is a prerequisite to alleviate rural poverty and improve livelihoods. Legumes have shown great potential to enhance system productivity. On-farm experiments were conducted in different agro-ecological zones (AEZ) in Western Kenya to assess the agronomic and economic benefits of promising legumes. In each zone, trials were established in fields of high, medium and low fertility to assess the effect of soil fertility heterogeneity on legume productivity and subsequent maize yield. Common bean, soybean, groundnut, lima bean, lablab, velvet bean, crotalaria, and jackbean were grown in the short rains season, followed by maize in the long rains season. Alongside, continuous maize treatments fertilised at different rates were established. AEZs and soil fertility gradients within these zones greatly affected crop productivity, returns to land and labour of rotations, as well as the relative performance of rotations. Poorer soil fertility and AEZs with lower rainfall gave smaller legume and maize yields and consequently, smaller returns to land and labour. The cultivation of legumes increased maize yields in the subsequent long rains season compared with continuous maize receiving fertiliser at a similar rate, while the increase of maize after green manure legumes was stronger than that after grain legumes. Maize yield responded strongly to increasing amounts of N applied as legume residues with diminishing returns to legume-N application rates above 100kgNha−1. In the low potential zones, factors other than improved N availability likely also stimulated maize yield. Rotations with grain legumes generally provided better returns than those with green manures. Intercropping bean with maize in the long rains season provided an additional bean yield that did not come at the expense of maize yield and improved returns to land and labour, but more so in the high potential zones. The results demonstrate the strong impact of biophysical diversity on the productivity of the legumes and suggest the need for careful targeting of legume technologies to the different biophysical conditions.

Soil Heterogeneity and Soil Fertility Gradients in Smallholder Farms of the East African Highlands

Heterogeneity in soil fertility in these smallholder systems is caused by both inherent soil-landscape and human-induced variability across farms differing in resources and practices. Interventions to address the problem of poor soil fertility in Africa must be designed to target such diversity and spatially heterogeneity. Data on soil management and soil fertility from six districts in Kenya and Uganda were gathered to understand the determinants of soil heterogeneity within farms. Analysis of the variance of soil fertility indicators across 250 randomly selected farms (i.e., 2607 fields), using a mixed model that considered site, sampling frame, farm type, and field as random terms, revealed that the variation in soil organic C (6.5–27.7 g kg−1), total N (0.6–3.0 g kg−1), and available P (0.9–27 mg kg−1) was mostly related to differences in the inherent properties of the soils across sites (50 to 60% of total variance). Exchangeable K+ (0.1–1.1 cmol(+) kg−1), Ca2+ (1.5–14.5 cmol(+) kg−1), Mg2+ (0.6–3.7 cmol(+) kg−1), and pH (5.1–6.9) exhibited larger residual variability associated with field-to-field differences within farms (30 to 50%). Soil fertility indicators decreased significantly with increasing distance from the homesteads. When this variable was included in the model, the unexplained residual variances—associated with soil heterogeneity within farms—were 38% for soil C; 32% for total N; 49% for available P; 56, 49, and 38% for exchangeable K+, Ca2+ and Mg2+, respectively; and 49% for the pH. In allocating nutrient resources, farmers prioritized fields they perceived as most fertile, reinforcing soil heterogeneity. Categorization of fields within a farm with respect to distance from the homestead, and soil fertility classes as perceived by farmers, were identified as entry points to target soil fertility recommendations to easily recognizable, distinct entities.

Identifying factors limiting legume biomass production in a heterogeneous on-farm environment

SUMMARYMultipurpose legumes provide a wide range of benefits to smallholder production systems in the tropics. The degree of system improvement after legume introduction depends largely on legume biomass production, which in turn depends on the legumes’ adaptation to environmental conditions. For Canavalia brasiliensis (canavalia), an herbaceous legume that has been recently introduced in the Nicaraguan hillsides, different approaches were tested to define the biophysical factors limiting biomass production on-farm, by combining information from topsoil chemical and physical properties, topography and soil profiles.Canavalia was planted in rotation with maize during two successive years on 72 plots distributed over six farms and at contrasting landscape positions. Above-ground biomass production was similar for both years and varied from 448 to 5357 kg/ha, with an average of 2117 kg/ha. Topsoil properties, mainly mineral nitrogen (N; ranging 25–142 mg/kg), total N (Ntot; 415–2967 mg/kg), soil organic carbon (SOC; 3–38 g/kg) and pH (5·3–7·1), significantly affected canavalia biomass production but explained only 0·45 of the variation. Topography alone explained 0·32 of the variation in canavalia biomass production. According to soil profiles descriptions, the best production was obtained on profiles with a root aggregation index close to randomness, i.e. with no major obstacles for root growth. When information from topsoil properties, topography and soil profiles was combined through a stepwise multiple regression, the model explained 0·61 of the variation in canavalia biomass (P &lt; 0·001) and included soil depth (0·5–1·70 m), slope position, amount of clay (19–696 kg/m2) and stones (7–727 kg/m2) in the whole profile, and SOC and N content in the topsoil. The linkages between topsoil properties, topography and soil profiles were further evaluated through a principal component analysis (PCA) to define the best landscape position for canavalia cultivation.The three data sets generated and used in the present study were found to be complementary. The profile description demonstrated that studies documenting heterogeneity in soil fertility should also consider deeper soil layers, especially for deep-rooted plants such as canavalia. The combination of chemical and physical soil properties with soil profile and topographic properties resulted in a holistic understanding of soil fertility heterogeneity and shows that a landscape perspective must be considered when assessing the expected benefits from multipurpose legumes in hillside environments.

Managing soil fertility diversity to enhance resource use efficiencies in smallholder farming systems: a case from Murewa District, Zimbabwe

Smallholder farms in sub-Saharan African exhibit substantial heterogeneity in soil fertility, and nutrient resource allocation strategies that address this variability are required to increase nutrient use efficiencies. We applied the Field-scale resource Interactions, use Efficiencies and Long-term soil fertility Development (FIELD) model to explore consequences of various manure and fertilizer application strategies on crop productivity and soil organic carbon (SOC) dynamics on farms varying in resource endowment in a case study village in Murewa District, Zimbabwe. FIELD simulated a rapid decline in SOC and maize yields when native woodlands were cleared for maize cultivation without fertilizer inputs coupled with removal of crop residues. Applications of 10 t manure ha−1 year−1 for 10 years were required to restore maize productivity to the yields attainable under native woodland. Long-term application of manure at 5 and 3 t ha−1 resulted in SOC contents comparable to zones of high and medium soil fertility observed on farms of wealthy cattle owners. Targeting manure application to restore SOC to 50–60% of contents under native woodlands was sufficient to increase productivity to 90% of attainable yields. Short-term increases in crop productivity achieved by reallocating manure to less fertile fields were short-lived on sandy soils. Preventing degradation of the soils under intensive cultivation is difficult, particularly in low input farming systems, and attention should be paid to judicious use of the limited nutrient resources to maintain a degree of soil fertility that supports good crop response to fertilizer application.

Impacts of heterogeneity in soil fertility on legume-finger millet productivity, farmers’ targeting and economic benefits

Targeting of integrated management practices for smallholder agriculture in sub-Saharan Africa is necessary due to the great heterogeneity in soil fertility. Experiments were conducted to evaluate the impacts of landscape position and field type on the biomass yield, N accumulation and N2-fixation by six legumes (cowpea, green gram, groundnut, mucuna, pigeonpea and soyabean) established with and without P during the short rain season of 2005. Residual effects of the legumes on the productivity of finger millet were assessed for two subsequent seasons in 2006 in two villages in Pallisa district, eastern Uganda. Legume biomass and N accumulation differed significantly (P < 0.001) between villages, landscape position, field type and P application rate. Mucuna accumulated the most biomass (4.8–10.9 Mg ha−1) and groundnut the least (1.0–3.4 Mg ha−1) on both good and poor fields in the upper and middle landscape positions. N accumulation and amounts of N2-fixed by the legumes followed a similar trend as biomass, and was increased significantly by application of P. Grain yields of finger millet were significantly (P < 0.001) higher in the first season after incorporation of legume biomass than in the second season after incorporation. Finger millet also produced significantly more grain in good fields (0.62–2.15 Mg ha−1) compared with poor fields (0.29–1.49 Mg ha−1) across the two villages. Participatory evaluation of options showed that farmers preferred growing groundnut and were not interested in growing pigeonpea and mucuna. They preferentially targeted grain legumes to good fields except for mucuna and pigeonpea which they said they would grow only in poor fields. Benefit-cost ratios indicated that legume-millet rotations without P application were only profitable on good fields in both villages. We suggest that green gram, cowpea and soyabean without P can be targeted to good fields on both upper and middle landscape positions in both villages. All legumes grown with P fertiliser on poor fields provided larger benefits than continuous cropping of millet.

Comparison of three chemical control strategies for Avena sterilis ssp. ludoviciana

The relatively high cost of Avena sterilis ssp. ludoviciana herbicides makes necessary the development of application strategies that maximize the efficacy with a minimum cost. Three herbicide strategies (spray at full and half doses and patch spray adjusting the doses to A. sterilis density) were compared in relation with control efficacy and crop yield in a winter barley field during three years. The results varied slightly within the years but, in general, the highest control levels and barley yields were obtained with the treatments at full dose. Using half doses reduced both A. sterilis control and barley yields. This effect was mainly attributed to the poor performance of low doses with high weed densities. The site-specific treatments resulted in the highest variability in the control and yield levels, with some control failures in areas of low density of A. sterilis. Barley yields were more affected by the zone effect (position of the plot within the field) than by the weed density effect. This fact was probably attributed to the relatively high heterogeneity in soil fertility within the field. Although the most profitable strategy in this specific situation was treating the whole field at full dose, this was probably due to the high percentage of the field infested by this weed. Different conclusions may be reached under different situations.

Effects of resource availability and heterogeneity on the slope of the species‐area curve along a floodplain‐upland gradient

AbstractQuestion:What are the relative effects of resource availability and heterogeneity on the slope of the species‐area curve along a floodplain‐upland gradient?Location:Réserve Léon‐Provancher, Québec, Canada.Methods:The mean and coefficient of variation of several environmental variables (soil organic matter, N and pH; irradiance; elevation) were estimated in 70 plots along a floodplain‐upland gradient. The slope of the species‐area curve was calculated from subplots nested within each plot. Path analysis was used to determine the effects of the environmental variables on the slope of the species‐area curve.Results:Spatial variation in flooding intensity created a complex gradient along which resource availability, but not resource heterogeneity, varied. Together, the environmental variables explained 73% of the variance in the slope of the species‐area curve. Elevation, soil variables (but not light) and heterogeneity in soil fertility (but not in light) were all significantly associated with the slope of the species‐area curve. Resource availability explained three times as much of the variance as resource heterogeneity.Conclusion:The expected positive relationships between resource availability, resource heterogeneity and diversity were obscured by effects of flooding stress and species dominance. Flooding intensity varies inversely with elevation and restricts the pool of species that can occupy the more fertile/heterogeneous section of the gradient, i.e. near the river. The few species combining flooding stress tolerance and competitive ability use the abundant resources near the river to grow quickly and utilize space, thereby enhancing the negative effect of the flooding stress on diversity.

Effects of resource availability and heterogeneity on the slope of the species-area curve along a floodplain-upland gradient

Abstract Question: What are the relative effects of resource availability and heterogeneity on the slope of the species-area curve along a floodplain-upland gradient? Location: Reserve Leon-Provancher, Quebec, Canada. Methods: The mean and coefficient of variation of several environmental variables (soil organic matter, N and pH; irradiance; elevation) were estimated in 70 plots along a flood-plain-upland gradient. The slope of the species-area curve was calculated from subplots nested within each plot. Path analysis was used to determine the effects of the environmental variables on the slope of the species-area curve. Results: Spatial variation in flooding intensity created a complex gradient along which resource availability, but not resource heterogeneity, varied. Together, the environmental variables explained 73% of the variance in the slope of the species-area curve. Elevation, soil variables (but not light) and heterogeneity in soil fertility (but not in light) were all significantly associated wi...

Soil heterogeneity effects on canopy structure and composition during early succession

Early succession from annuals to herbaceous and woody perennials on abandoned fields and grasslands is marked by vegetation heterogeneity; i.e., variation in canopy composition and structure over the field through time. Soil resource heterogeneity could promote vegetation heterogeneity. We created soil resource patchiness on two newly ploughed fields by establishing two types (fertilized, unfertilized) of checkerboard plots with two, four, or eight subplots (trenched, untrenched) to test effects of soil fertility heterogeneity scale on vegetation heterogeneity during early succession. Canopy composition and structure were censused in years 2, 4 and 6. On both fields, soil resource heterogeneity did not affect canopy composition or structure. Differential abundance of dominant species, Ambrosia trifida on one field and Solidago altissima on the other, between fertilized and unfertilized plots led to decreased vegetation heterogeneity among subplots within plots and increased vegetation heterogeneity among plots. Soil enrichment promoted taller and layered, but species-poor, canopy. In general, soil fertility effects on abundance, expansion, and dominance of individuals of dominant species promoted variation in canopy composition and structure, or vegetation heterogeneity, among plots on the two fields.