Soil Organic Matter Management Research Articles

Conversion of Natural Soil to Paddy Promotes Soil Organic Matter Degradation in Small-Particle Fractions: δ13C and Lipid Biomarker Evidence

The stabilization mechanism of soil organic matter (SOM) has received considerable attention. It is widely accepted that mineral sorption/protection is important for SOM stabilization. However, it remains unclear which organic carbon component is beneficial for mineral protection. We collected soil samples from a paddy field (TP) to compare with natural soil (NS). To illustrate the behavior of different SOM pools and their protection by particles, we separated the soils into different particle-size fractions and then removed the active minerals using an acid mixture (1 M HCl/10% HF). The different carbon pools were analyzed using stable carbon isotopes and lipid biomarkers. Our study showed that acid treatment evidently increased the extractability of free lipids, usually over 60%, which confirmed the predominant role of minerals in SOM protection. For NS, the δ13C values increased with decreasing soil particle sizes and soil depths, indicating that 13C-enriched SOM was selectively preserved. However, this trend disappeared after cultivation, which was mainly attributed to the combined effects of the input of 13C-depleted fresh SOM and decomposition of the preserved 13C-enriched SOM. Meanwhile, based on the degradation parameters of the overall lipid biomarkers, SOM showed higher degradation states in clay and silt fractions than in the sand fraction before cultivation. It is possible that the small particle-size fractions could selectively absorb highly degraded SOM. The clay-associated SOM showed a low degradation state, but its carbon content was low after cultivation. We propose that the previously protected SOM was degraded after cultivation and was replaced by relatively fresh SOM, which should be carefully monitored during SOM management.

Stand age and soil organic matter management as driven factors of soil biota community composition and soil chemical properties in a subtropical Acrisol

AbstractPyrus pyrifolia is a common temperate fruit crop cultivated in Southern Brazil for fruit production. Although this plant species is found in several Brazilian states (Paraná, Santa Catarina, São Paulo, Rio Grande do Sul), it is predominantly concentrated in the smallholder farming system in Santa Catarina, Brazil. Our aim was to compare the soil biota community composition, soil chemical properties, and soil quality in two adjacent stands with different ages. Within each stand, we analysed the influence of four organic residue management practices. Our results indicated that both studied stands, influenced by different organic residue management practices, exhibited differences in soil biota community composition, soil chemical properties, and soil quality. Acaridae, Araneidae, Blattidae, Halictophagidae, and Opiliones were the main contributors, explaining 78.08% of the variance in the data. The 16‐year‐old stand, with compost utilization, displayed a high biodiversity of soil organisms, average soil chemical properties, and the highest values of soil quality, creating a habitat for predators and providing energy for litter transformers and ecosystem engineers in subtropical Acrisol. These findings contribute to a deeper understanding of the influence of old stands on soil biota community composition, soil chemical properties, ecosystem homeostasis, herbivory pressure, and prey‐predation relationships. This, in turn, may enhance interest in establishing new management plans for Pyrus pyrifolia stands in commercial orchards.

Tree-Based Modeling for Large-Scale Management in Agriculture: Explaining Organic Matter Content in Soil

Machine learning (ML) has become more prevalent as a tool used for biogeochemical analysis in agricultural management. However, a common drawback of ML models is the lack of interpretability, as they are black boxes that provide little insight into agricultural management. To overcome this limitation, we compared three tree-based models (decision tree, random forest, and gradient boosting) to explain soil organic matter content through Shapley additive explanations (SHAP). Here, we used nationwide data on field crops, soil, terrain, and climate across South Korea (n = 9584). Using the SHAP method, we identified common primary controls of the models, for example, regions with precipitation levels above 1400 mm and exchangeable potassium levels exceeding 1 cmol+ kg−1, which favor enhanced organic matter in the soil. Different models identified different impacts of macronutrients on the organic matter content in the soil. The SHAP method is practical for assessing whether different ML models yield consistent findings in addressing these inquiries. Increasing the explainability of these models means determining essential variables related to soil organic matter management and understanding their associations for specific instances.

Addition of biochar decreased soil respiration in a permanent no-till cover crop system for organic soybean production

The increase in soil carbon sequestration under long-term no-till (NT) and cover crop management has been shown to form part of a sustainable agricultural management practice system. Along with the increase in soil organic carbon (SOC), soil respiration in this system was also enhanced by the increased soil temperature through the decomposition that causes carbon loss from the soil. To overcome this issue, biochar can be applied. However, the addition of biochar into this system is not well studied. Therefore, the aim of this study was to investigate the effect of this system on soil respiration. The experiment was conducted at the Center for International Field Agriculture Research & Education, Ibaraki University. Long-term tillage practices, such as NT and moldboard plowing (MP), cover crops such as rye (RY) and fallow (FA), and biochar application such as with biochar (WB) and no biochar (NB) were applied to a split–split plot in a randomized complete block design with four replications. The daily CO2 flux was measured every week at 9:00–11:00 a.m. The daily soil respiration was affected by tillage and cover crop with NT practice had significantly higher daily CO2 flux than that of MP (23.8%–107.4% and 38.0%–107.8%), while RY had higher flux than that of FA (11.9%–81.2% and 34.9%–65.4%) in 2020 and 2021 soybean growing season, respectively. Additionally, in the 2020 cover crop growing season RY also increased daily CO2 flux approximately 41.8%–88.2% compared to FA. Biochar addition significantly reduced soil respiration in soybean and cover crop seasons compared to NB by 24.0%–50.7% and by 25.9%–48.3%, respectively. This reduction in soil respiration by the biochar decreased annual CO2 emissions by 17.6% and 13.0% in 2020 and 2021. The values of these emissions ranged from 9.6 Mg ha−1 for MP FA WB to 18.9 Mg ha−1 for MP RY NB in 2020 and from 7.5 Mg ha−1 for MP FA WB to 13.7 Mg ha−1 for NT FA NB in 2021. This study highlights the crucial role of biochar in reducing soil respiration and enhancing SOC sequestration. The addition of biochar into this system was able to reduce soil respiration by regulating the soil temperature, soil moisture, and protect the SOC from decomposition. Biochar addition also increased the SOC and decreased the soil bulk density, which improves soil porosity. Therefore, these findings would be very useful to be included within the global scenario of soil organic matter management.

Soil organic mater management – a decisive measure in climate change mitigation and adaptation

Global warming requires the implementation of both immediate and long-term mitigation and adaptation measures in agriculture, which is affected by greenhouse gas emissions through the use of practices from the industrial model arsenal of agricultural intensification (oversaturation of planting areas with arable crops and lack of crop rotations with a greater diversity of arable and successive crops; excessive tillage; irrigation; application of mineral fertilizers, especially nitrogen etc.). Data from the long-term field experiments at Research Institute of Field Crops ”Selecția” (Bălți, Republic of Moldova) are proving the dominance of mineralization over humification of soil organic matter with the emissions of CO2 and oxides of nitrogen in the atmosphere. Chernozem soils have a high potential for carbon sequestration and consequently for mitigation and adaptation to climate change. Sustainable and resilient management of soil organic matter is one of the key issues for the transition to a more sustainable agriculture, capable to supply ecosystem and social services.

Salt-affected soils: field-scale strategies for prevention, mitigation, and adaptation to salt accumulation

The area of salt-affected soils is increasing globally, mainly due to land use and management malpractices, which can threaten soil health and the sustainability of farms. Climate change is likely to increase the prevalence of salt-affected soils in many agricultural areas due to increased aridity and, in coastal areas, due to the increase in sea water level. The causes and processes that develop salt-affected soils are diverse and can result in soil salinity, sodicity, alkalinity, or a combination of these conditions. There is a need to continuously update strategies to tackle salt-affected soils, finding solutions tailored at different scales. This work presents a review of the current knowledge related to salt-affected soils and identifies specific strategies and related case studies for the prevention, mitigation, and adaptation to salt accumulation in soils at the field scale while addressing their limitations, advantages, research needs, and innovation potential. The presented case studies show that adequate irrigation management and drainage can be used as a preventive measure to counter salt accumulation in soils. Phyto and bioremediation can be effective practices for the mitigation of soil sodicity. Leaching and drainage can be effective measures for mitigation of soil salinity. Crop rotation and management of soil organic matter can be used as adaptative measures that improve plant tolerance to salt-affected soils, while a newer approach, microbial management, shows innovation potential as an adaptative measure.

IMPACT OF POTENTIALLY SOIL MINERALIZABLE NITROGEN (PMN) ON SOIL HEALTH AND CROP PRODUCTION

Potentially Soil Mineralizable Nitrogen (PMN) is critical in soil health and crop production. This review paper explores the impact of PMN on soil health, crop production, different soil types, and mitigation strategies. It highlights the importance of PMN in enhancing nutrient availability, crop yield, and quality. The paper discusses the role of PMN in promoting soil organic matter accumulation, supporting microbial activity, and improving soil physical properties. Case studies illustrate the influence of PMN on different soil types and associated crops. Mitigation and management strategies are discussed, such as soil organic matter management, precision nutrient management, and crop rotation/diversification. The review also identifies future research directions, including refining PMN measurement techniques, integrating into nutrient management decision support systems, and exploring PMN interactions with other soil properties and environmental factors. Overall, effective PMN management is crucial for sustainable agriculture, and further research and collaboration are needed to advance our understanding and develop practical strategies for its implementation.

THE IMPORTANCE OF SOIL ORGANIC MATTER (SOM) ON SOIL PRODUCTIVITY AND PLANT GROWTH

Soil organic matter (SOM) is vital to soil health and plays a critical role in crop production. This review paper examines the impact of SOM on soil health, crop production, and the challenges and opportunities associated with managing SOM. The paper emphasizes the importance of interdisciplinary research, technological advancements, and supportive policies in addressing SOM dynamics and management complexities. The review highlights the role of SOM in nutrient supply, soil structure improvement, water-holding capacity, and microbial activity enhancement, which are fundamental for sustainable agricultural systems. Various management practices to enhance SOM, including organic amendments, cover cropping, conservation tillage, and crop rotation, are discussed. Despite the benefits of managing SOM, challenges such as slow formation rates, trade-offs with other agricultural objectives, and economic viability exist. Addressing these challenges requires further research, knowledge exchange, and integrating traditional knowledge with modern technologies. Future perspectives and research needs include advancing interdisciplinary collaboration, harnessing emerging technologies, understanding the interactions between SOM and climate change, exploring novel management practices, quantifying ecosystem services, addressing knowledge gaps, and providing policy support and incentives. Sustainable soil management strategies can be developed by embracing these perspectives and addressing the identified research needs. These strategies optimize SOM levels, promote soil health, enhance crop productivity, and contribute to global food security and environmental sustainability. Overall, this review provides valuable insights for researchers, policymakers, and stakeholders in their efforts to enhance SOM management and promote sustainable agriculture.

Matured Manure and Compost from the Organic Fraction of Solid Waste Digestate Application in Intensive Apple Orchards

In intensive fruit growing systems, the recovery and maintenance of soil fertility play a crucial role in both environmental protection and sustainable support to plant productivity. The circular economy approach adopted at the EU level strongly promotes the use of organic products instead of mineral fertilizers. This work focuses on two different soil improvers, compost from the organic fraction of municipal solid waste digestate (CO) and "matured" manure, produced after a fast and controlled aerobic treatment in an aerated pile (MM), which were applied in three apple orchards with different soil tillage. The soil improvers have been characterized for amendment and fertilizing properties. After the amendment, the soils were sampled twice a year (Spring and Autumn) for three years. Each sample has been characterized for texture, pH, cation exchange capacity, nutrients, soil organic matter, and micronutrients. The amendments obtained differed on C, N, P, and K contents, but had similar biological stability. The main effects on soils were the increasing of N and soil organic matter after compost application, while the use of matured manure mainly act on available P and exchangeable K. The treatments showed significant effects among fields with a linear increasing trend only for compost. Matured manure showed more effects in earlier times. The data collected aim to improve the knowledge about sustainable management of soil organic matter and organic nutrients in intensive fruit-growing agriculture by using local products.

Spatial Variability of the Organic Matter in the Soil in Cassava Cultivation Under Differentiated Management

The management of soil organic matter (SOM) is fundamental in agriculture for soil conservation and crop yields. However, in addition the soil being dynamics, it is heterogeneous, therefore, understanding the spatial variability of SOM is essential. The main objective of this study was to evaluate the spatial variability of SOM in a cassava cultivation under different management, seeking to classify its spatial dependence by geostatistics. A filed experiment was conducted out on soil classified as oxisol with four different management systems: irrigation (micro sprinkler, drip and no irrigation), spacing (1.0 × 0.8 m, 1.0 × 1.0 m and 1.0 × 1.5 m), weed control (manual control and no control) and acidity correction (limestone and withouth limestone), totaling 36 experimental plots. To determine the SOM, the wet oxidation method was used, and the semivariograms were generated by the GS+® software. The effect of the different management systems on the spatial variability of the SOM was evaluated at a depth of 0.0-0.2 m. The theoretical semivariogram model that best fitted the study was the Gaussian model, with a well-defined level, also expressing the condition of data stationarity. The spatial dependence was classified as strong and, through the thematic map generated from the kriging, it was possible to observe the variability in the SOM content for different management zones. The use of geostatistics techniques provided important information for understanding the spatial distribution of soil organic matter.

The Composition of the Organic Matter Fractions of Loamy Sand after Long-Term FYM Application without Liming

The key to soil organic matter management is understanding the transformation processes of fresh organic matter to permanent humus that control soil organic carbon dynamics. This paper presents the results of the effect of long-term soil fertilization with increasing doses of (manure) FYM and ammonium nitrate on the composition of humus compounds not limed of loamy sand. The study showed that both crop rotation and manure fertilization significantly affected organic matter fractions and humus humification index. The soil in crop rotation B (with enriching effect) accumulated significantly larger amounts of soil organic carbon in 0–30 cm layer despite a lower soil pH, but had lower soil organic quality compared to the soil in crop rotation A (with depleting effect). In both rotations, FYM was applied once per 4-year rotation at a dose of 40 t·ha−1 which improved the soil organic carbon content. Depleting crop rotation (A) showed no increase in soil accumulation of humins fractions (H), while the “enriching” crop rotation (B) had such a tendency. Mineral nitrogen fertilization significantly affected the composition of the humic acids fraction. The soil in crop rotation B was characterized by a significantly higher content of fulvic acid (FA) and lower of humins (H) carbon fraction. The large input of organic matter into the soil under lower content pH conditions may hinder its transformation into permanent humus. Changes in the humification index were the consequence of changes in the carbon content of humic and fulvic acids, under the influence of plant selection in crop rotation and manure fertilization. According to the criterion of this parameter, soil in crop rotation A and soil fertilized with manure had lower loss of the more labile FA fraction (lower value of humification index—1.48).

Potential tradeoffs between effects of arbuscular mycorrhizal fungi inoculation, soil organic matter content and fertilizer application in raspberry production.

Ecological intensification has been proposed as an alternative paradigm for intensive agriculture to boost yield sustainably through utilizing ecosystem services. A prerequisite to achieving this is to understand the relations between multiple ecosystem services and production, while taking growth conditions such as nutrient availability into consideration. Here, we conducted a pot-field experiment to study the interactive effects of soil organic matter (SOM) content and arbuscular mycorrhizal fungi (AMF) inoculation on the production of raspberry (Rubus idaeus L.) under four levels of fertilizer application. Raspberry flower number, fruit number and yield only significantly increased with fertilizer inputs but were not impacted by SOM content or AMF inoculation. Fruit set and single berry weight were influenced by both SOM content and AMF inoculation, in complex three-way interactions with fertilizer application. Fruit set of AMF inoculated plants increased with fertilizer inputs in low SOM soils, but decreased with fertilizer inputs under high SOM soils, with the highest fruit set occurring at no fertilizer inputs. In low SOM soils, the relation between single berry weight and fertilizer application was more pronounced in inoculated plants than in non-inoculated plants, while in high SOM soils the relative benefits of AMF inoculation on single berry weight decreased with increasing fertilizer inputs. We attribute the lack of effects of AMF inoculation and SOM content on flower number, fruit number and yield mainly to potential tradeoffs between the experimental variables that all influence resource uptake by plant root systems. Our results suggest that potentially beneficial effects of AMF and SOM can be offset by each other, probably driven by the dynamic relations between AMF and the host plants. The findings reveal fundamental implications for managing AMF inoculation and SOM management simultaneously in real-world agricultural systems.

Local ecological knowledge of coffee agroforestry farmers on earthworms and their relation to soil quality in East Java (Indonesia)

Abstract. Mardiani MO, Kusumawati IA, Purnamasari E, Prayogo C, van Noordwijk V, Hairiah K. 2022. Local ecological knowledge of coffee agroforestry farmers on earthworms and their relation to soil quality in East Java (Indonesia). Biodiversitas 23: 3344-3354. Farmers manage their land-based on their understanding of biotic and abiotic factors, including soils, and how these factors affect crop growth and productivity. Their local ecological knowledge (LEK) is built upon intergenerational transfer and can use concepts that don’t directly match those of current science-based ecological knowledge. We explored farmer LEK related to soil organic matter management and earthworms in coffee-based agroforestry systems on volcanic slopes in East Java (Indonesia) by in-depth interviews with key informants and by surveying the concurrence of respondents, stratified by gender and age, with resulting statements. The term used in the local language for earthworms (‘cacing tanah’) included a range of species. According to 22% (n=48) of farmers, small earthworms (probably Pontoscolex corethrurus) are harmful to coffee trees because they eat the roots. Also, 54% (n=48) of farmers thought earthworms that eat soil cause a decrease in soil volume. However, according to the farmers, large earthworms (reddish-brown) can fertilize the soil by leaving their casts on the soil surface. Such worms are often found in coffee agroforestry systems. Farmers have little explicit knowledge of the activities of earthworms and their relation with litter as a source of food. Farmer knowledge of ecosystem services provided by earthworms can enrich current scientific literature and trigger a two-way dialogue.

ASSESSMENT OF SOIL ORGANIC MATTER MANAGEMENT IN POLISH AGRICULTURE

The subject of this study was the analysis of the soil organic matter (SOM) management in Polish agriculture in 2017-2019. The comparative analysis in spatial arrangement was carried out at the level of polish voivodeships. SOM balance was prepared in a simplified way, using it is degradation and reproduction coefficients proposed by Eich and Kundler. During 2017-2019, the balance of SOM was at level of 0.07 t DM/ha arable land (ArL). Positive balance of SOM was found in most voivodeships of Poland, and by far the highest in two voivodeships: Podlaskie and Warmińsko-Mazurskie, where manure and slurry resources were the largest. The negative SOM balance ranged from -0.02 t DM/ha ArL in Lubuskie to -0.14 t DM/ha ArL in Dolnośląskie, and the main reason for this was low natural fertilizer supply. In those voivodships the amount of ploughed-in plant material was insufficient to cover the losses of SOM caused by plant cultivation. The analysis of SOM management confirmed high polarisation between individual voivodships, together with the processes of extensification of production organisation (specialisation), with a simultaneous increase in it is intensity and scale of concentration.

Strategies for efficient estimation of soil organic content at the local scale based on a national spectral database

AbstractSoil function degradation threatens the sustainable management of soil resources and soil organic matter (SOM) is a vital and important factor. Powerful measuring tools will become very important, especially in areas where data are poor or absent. The archive: China Soil Visible and Near Infrared (vis–NIR) Spectroscopy Library (CSSL) could help providea solution for less costly and fast measuring of SOM. The aim of this article was to compare SOM prediction performance according to three strategies: i) general global partial least squares regression (PLSR) using CSSL with and without spiking samples; ii) memory‐based learning (MBL) using CSSL with and without spiking samples; and iii) general PLSR using only spiking samples to predict soil organic matter in the target area. When using spiked subsets, we also investigated the prediction performance of the extra‐weighted (several copies) subsets. A series of spiking subsets were randomly selected from the total spiking samples, which were selected by conditioned Latin hypercube sampling (cLHS) from the target sites. We calculated only the mean squared Euclidean distance (msd) between the estimates density function (pds) of the principal components (PCs) of vis–NIR spectroscopy from the validation dataset and spiking subsets and statistically inferred the optimal sampling set size to be 30. Our study showed that global PLSR using CSSL spiked with the statistically optimal local samples can achieve higher predicted performance [with a mean root mean square error (RMSE) of 5.75]. MBL spiked with five extra‐weighted optimal spiking samples achieved the best accuracy with an RMSE of 3.98, an R2 of 0.70, a bias of 0.04, and an LCCC of 0.81. The msd is a simple and effective method to determine an adequate spiking set size using only vis–NIR data. These accurate predictions demonstrated the usefulness of statistically representative spiking and MBL for advanced large soil spectral libraries for SOM determination, which is currently lacking at large soil spectral libraries in use.

Catching change in microbial diversity indicators under different soil organic matter managements: Higher taxonomic resolution, better discrimination?

Recent advances in molecular ecology have dramatically improved our knowledge of soil microbial diversity and offers new indicators of soil quality. The usefulness of diversity indices has never been greater as the astronomical amounts of data generated in the literature needs to be synthesized. Despite technical guidelines have been proposed to characterize soil microbiomes using high throughput sequencing, the effect of taxonomic resolution on diversity indices is still largely unknown. Here, we explored how downscaling to higher taxonomic resolution levels may affect α- and β-diversity indices of bacterial communities exposed to different soil organic matter management. To this aim, we collected soil samples in a long-term experimental site (Ultuna, Sweden) where different mineral and organic fertilizers have been applied for since 1956. We used both massive amplicon sequencing from phylum to species (OTU) and molecular fingerprints (PLFA, DGGE and T-RFLP). Our results showed that the discrimination potential increased at finer taxonomic resolution for β-diversity but not for α-diversity indices such as richness and evenness. Also, the relative importance of hierarchical drivers of soil microbial communities such as C, N and pH varied depending on the taxonomic resolution. This study also demonstrated that indicators generated by molecular fingerprints such as PLFA, DGGE and T-RFLP are still consistent to monitor the effect of agricultural management on β-diversity but not on α-diversity, which is useful information as it allows for a better use of results in past literature. We encourage performing such comparative studies on wider surveys, including different contexts and other indicators, in order to increase the efficiency and the robustness of the use of sequencing data in soil biodiversity monitoring.

Plant hormone crosstalk mediated by humic acids

BackgroundThe reliance on chemical inputs to support high yields is the Achilles’ heel of modern crop production. The soil organic matter management is as old as agriculture itself. Recently, the use of soluble humic substances as plant growth promoters has been brought to attention due to their effects on nutrient uptake and water use efficiency. Humic substances applied directly at low concentrations can trigger different molecular, biochemical, and physiological processes in plants. However, how humic substances exert this plethoric regulatory action remains unclear. The objective of this study was to evaluate changes in the transcription level of genes coding cell receptors, phosphatases, synthesis, and function of different plant hormones and transcription factors.Materials and methodsAfter seven days of humic acid treatment, we used RNAseq in maize root seedlings. The level of gene transcription was compared with control plants.ResultsPlant kinase receptors and different phosphatases were regulated by humic acids. Likewise, genes related to plant hormones (auxin, gibberellin, ethylene, cytokinin, abscisic acid, brassinosteroids, jasmonic and salicylic acids) were transcript in differential levels in maize root seedlings as well as the expression of a hundred of transcription factors modifying the signal transduction pathway via alterations of the subsequent gene response.ConclusionWe showed a general mechanism for simultaneously regulating the activity of several hormones where humic acids act as a key regulatory hub in plant responses integrating hormonal signalling and response pathways.

Crop rotation and soil fertility – limiting factors in ensuring the sustainable development of agriculture in the Republic of Moldova

The article comprises experimental data obtained from long-term tests in crop rotations and permanent crops carried out at ”Selectia” Research Institute of Field Crops.They confirm the possibility of significantly reducing the dependence of agriculture on the use of mineral fertilizers and pesticides for diseases,pests and weeds control,irrigation water etc.The effect of fertilization is considerably higher in the permanent crop and at the incorrect alternation of the crops after the predecessors,compared to the effect of crop rotation.The efficiency of using nitrogen from mineral fertilizers is relatively low which increases the risk of global warming by emission of nitrogen oxides in the atmosphere. The share of soil fertility in the formation of yields for most crops is dominant due to the relatively small share of nitrogen from mineral fertilizers in the total nitrogen extract.The sustainable and resilient management of soil organic matter is crucial in order to ensure a viable development of agricultural sector in the Republic of Moldova.Agriculture can provide both the country”s food security and its energy security.

Onion-forage cropping systems on a Vertic Argiudoll in Uruguay: Onion yield and soil organic matter, aggregation, porosity and permeability

Hostipastoral systems in small farming units that integrate horticulture crops, as main cash crop, with sheep/cattle raising on cultivated forage, in Uruguay, present physical restrains to crops because of high consistency and compaction of the vertic soils and unique tillage requirements. The objective of this study was to evaluate the effect of different hortipastoral systems on soil organic matter, aggregation, porosity, permeability and onion yield during a cropping year in onion-forage hortipastoral systems. A long-term experiment was installed in 1995 in the National Institute for Agricultural Research (INIA-Las Brujas) in Uruguay, on fine (mixed) smectitic thermic superactive Vertic Argiudolls. The soil was previously under native grasslands, and treatments consisted of cropping systems for onion (Allium cepa L.) production, maintained for three years and then rotated. Onion yield was evaluated during the period 1998–2006, and in the cropping year 2006–2007, corresponding to the end of a 3-year cropping cycle, we evaluated soil organic matter and physical properties and functioning in the cropping systems: alfalfa, fescue, forage consortium (birdfoot trefoil, alfalfa and white clover), onion after alfalfa, onion after fescue, and onion after consortium. At four times during the cropping year, aggregate stability and organic matter were determined for the 0–0.05 m soil layer, whereas soil bulk density, porosity, and hydraulic conductivity were determined in 0–0.10 and 0.10–0.20 m layers. The results showed high variability in onion yields from 1998 to 2006 (10.8–36.4Mgha−1), mainly related to high rainfall (higher than 150 mm) that affected crop planting, and the low rainfall (lower than 30 mm) that affected growth and development. In two out of eight years, there were significant differences in onion yield among treatments, where alfalfa (1999) and fescue (2006) crops are more beneficial to onion yield than pasture consortium. To establish the onion crop in the vertic soil tillage is needed, but tilling the soil under forage crops reduces macro and increases microaggregation (reduces GMDw from 1.8 to 0.8 mm), increases macroporosity (close 0.07 to 0.25 m3 m−3) and functioning in terms of water and air permeability (Ka increase above 3 µm2 after tillage) and decreases the degree of compaction (under forages decreased DC from 69-84% to 58–60% in surface layer). In conclusion, there is a significant potential of hortipastoral systems and proper management of soil organic matter to minimize adverse effects of climate, and improve productivity stability of intensive production systems. Single forage crops, either legume or grass, are more beneficial to onion yield than consortium of grass plus legumes.

APPLICATION OF FRACTAL THEORY IN QUANTIFYING SOIL AGGREGATE STABILITY AS INFLUENCED BY VARYING TILLAGE PRACTICES AND COVER CROPS IN NORTHERN GUINEA SAVANNA, NIGERIA

<p><strong>Background.</strong> Soil aggregate stability varies with management practices like tillage and soil organic matter management. <strong>Objective.</strong> The objectives of this study were to (i) Explore a fractal theory to investigate the extent of soil fragmentation in soil of Samaru, Northern Nigeria, subjected to different tillage practices and covers crops for the purpose of improving soil aggregate stability (ii) Establish a relationship between fractal dimension (D) and mean weight diameter (MWD). <strong>Methodology.</strong> A three years field trials was conducted with three tillage practices (no-till, reduced till and conventional till) as main treatments and four cover crops (<em>Centrosema pascuorum, Macrotyloma uniflorum, Cucurbita maxima</em> and <em>Glyine max</em>), and a bare/control (no cover crop) as sub treatments. The trial was laid out in randomized complete block design, split plot arrangement and replicated three times. Soil samples were collected at 0-15 cm prior to trial establishment for routine soil physical and chemical properties and at depths 0-5, 5-10, 10-15 and 15-20 cm at the end of each cropping season each year for soil aggregate stability test. <strong>Results. </strong>No-till soils had 12.58% better soil aggregate stability than soils under reduced and conventional tillage systems. Also, no-till soils had 2.40 % less fragmented soil aggregates than Reduced and Conventional till soil as indicated by the fractal dimension of soil aggregates. Soils under <em>Macrotyloma uniflorum</em> cover crop, were on the average 2.33% less fragmented than soils under <em>Centrosema pascuorum, Glycine max </em>and<em> Cucurbita maxima</em> but 4.56% less fragmented than soils with no cover crops. <strong>Implication, </strong>No-till and reduced till systems; and cover cropping better enhanced soil aggregate stability due to better accumulation of organic matter emanating from crop residues return to soil in these practices. <strong>Conclusion.</strong> Conservation tillage and the use of cover crops lowered soil aggregate fragmentation relative to conventionally tilled system and bare soil with no cover crop. The strong linear relationship established between MWD and fractal dimension showed over 80% dependency, suggesting that fractal dimension is another useful index for evaluating soil aggregate stability.</p><p>.</p>