Integrated Soil Fertility and Plant Nutrient Management in Tropical Agro-Ecosystems: A Review

The greatest challenge for tropical agriculture is land degradation and reduction in soil fertility for sustainable crop and livestock production. Associated problems include soil erosion, nutrient mining, competition for biomass for multiple uses, limited application of inorganic fertilizers, and limited capacity of farmers to recognize the decline in soil quality and its consequences on productivity. Integrated soil fertility management (ISFM) is an approach to improve crop yields, while preserving sustainable and long-term soil fertility through the combined judicious use of fertilizers, recycled organic resources, responsive crop varieties, and improved agronomic practices, which minimize nutrient losses and improve the nutrient-use efficiency of crops. Soil fertility and nutrient management studies in Ethiopia under on-station and on-farm conditions showed that the combined application of inorganic and organic fertilizers significantly increased crop yields compared to either alone in tropical agro-ecosystems. Yield benefits were more apparent when fertilizer application was accompanied by crop rotation, green manuring, or crop residue management. The combination of manure and NP fertilizer could increase wheat and faba bean grain yields by 50%–100%, whereas crop rotation with grain legumes could increase cereal grain yields by up to 200%. Although organic residues are key inputs for soil fertility management, about 85% of these residues is used for livestock feed and energy; thus, there is a need for increasing crop biomass. The main incentive for farmers to adopt ISFM practices is economic benefits. The success of ISFM also depends on research and development institutions to provide technical support, technology adoption, information dissemination, and creation of market incentives for farmers in tropical agro-ecosystems

Interactive Effect of Residue Quality and Agroecologies Modulate Soil C- and N-Cycling Enzyme Activities, Microbial Gene Abundance, and Metabolic Quotient

Understanding interactive effect of agroecology explained by rainfall, temperature, elevation, and biochemical composition of residues on soil microbial abundance and functions is crucial for unraveling soil ecological processes. This study aimed to investigate how agroecology and residue quality influence enzymatic activities, gene abundance, and metabolic quotient (qCO2). A field experiment was conducted using Leucaena leucocephala (LL) (high-quality residue) and Acacia decurrens (AD) (low-quality residue) in soils of highland and midland agroecologies. These residues differed in decomposability, characterized by a ratio of (lignin + polyphenol)/N of 5.0 for high-quality residue versus 21.0 for low-quality residue. Two experimental setups were employed: soil with litter mixture in polyvinyl chloride (PVC) tubes and residues buried in the surface soil using litterbags. Soil samples were collected after 30, 120, and 270 days of incubation and analyzed for biochemical properties, enzyme activities, and the abundance of nitrifying and total archaea and bacteria. Soil respiration was also measured at different intervals in the field. qCO2 was calculated using microbial biomass (MBC) and daily respiration (DCO2). Linear mixed model (P < 0.05) revealed that combined factors of agroecologies and residue qualities affected enzymatic activities, microbial abundance, soil properties, and qCO2. Agroecological differences exerted a greater influence than residue qualities. Positive and negative significant correlations (P < 0.05, r = 0.27 to 0.67) were found between different C and N pools as well as enzymatic activities. Positive correlations (P < 0.05) were observed between the abundance of total bacteria, total archaea, and ammonia-oxidizing bacteria versus leucine-aminopeptidases. qCO2 was influenced more by β-xylosidase, leucine-aminopeptidases, and thermolysin-like neutral metalloproteases (TLP) than by β-D-glucosidase and β-D-cellobiohydrolase. Leucine-aminopeptidases and TLP were identified as rate-limiting factors for protein and peptide decomposition, while β-xylosidase controlled hemicellulose degradation. In summary, this study provides insights into the intricate relationships between agroecology, residue quality, enzymatic activities, and microbial communities, shedding light on key processes governing soil ecological functions

Response of Teff ((Eragrostis tef (zucc.) Trotter) to nitrogen and phosphorus applications on different landscapes in eastern Amhara

The dynamic nature of soil fertility status across different landscapes attracted research attention in Ethiopia and the globe. Teff [Eragrotis tef] is a major staple cereal crop in Ethiopia but yields are low due to inadequate nutrient supply and other constraints. A field study was conducted in 2020 and 2021 in the Habru district of Amhara Region to determine teff yield response to fertilizer-N and -P at hillslope, midslope, and footslope positions with slopes of >15%, 5–15%, and 0–5%, respectively. N and P fertilizer rates were factorially combined in randomized complete block design with three replications in each farmer’s field. A linear mixed modeling framework was used to determine effects on grain yield due to N rate, P rate, slope, study sites, and years. Model fit was examined using Akaike’s Information Criterion and Bayesian Information Criterion. Economic analysis was done with a quadratic response function to determine the economics of fertilizer. Yield response to fertilizer-P was affected by slope but the response to fertilizer-N was not affected. Teff yield increase with fertilizer-N application up to 92 kg ha-1 the economic optimum rate based on the yield response function for nitrogen fertilizer was 85.4 kg ha-1 to obtain maximum profit (86878.8 birr ha-1). Similarly, the optimum phosphorus fertilizer rate at the hill slope was 39.7 kg ha-1 to obtain a maximum profit of (96847.8 birr ha-1). But there was not a profitable response at the midslope and foot slope positions. Therefore, for Habru district and similar agroecologies85.4 kg ha-1 N and 39.7 kg ha-1 P in hillslopes and only 85.4 N kg ha-1 for midslopes and foot slopes are expected to give the most profitable returns to fertilizer applied for tef production

Remediation of acid soils and soil property amelioration via Acacia decurrens-based agroforestry system

Land degradation and the associated soil acidity are critical challenge for crop production in Ethiopian highlands. Since liming is expensive, farmers have developed an alternative agroforestry system by integrating Acacia decurrens into their landscapes. The expansion rate of this system was assessed over the last three decades. The effects of the agroforestry system and charcoal-making kiln sites on soil properties were investigated for over five years compared to the adjacent croplands. Soil samples were collected from A. decurrens plantations, kiln sites, and adjacent croplands at 0–15 and 15–30 cm soil depths. In the last 30 years, the plantation and croplands increased by 8% and 17.5%, respectively, compared to the land-use system in 1993, mainly at the expense of grassland and abandoned land. The main incentive for expansion of A. decurrens plantations was farmers’ income generated from charcoal making. This intervention also improved soil properties with a significantly positive effect on soil pH, soil organic carbon (SOC), cation exchange capacity (CEC), and available Bray phosphorus (Bray-P) compared to the adjacent croplands. Results revealed that the SOC content in year 2 increased significantly (1.3–1.7 times) under A. decurrens plantation compared to adjacent crop fields. Moreover, soil pH increased by one unit on charcoalmaking fields, which was equivalent to application of 4–5 t lime ha-1, while SOC increased by * 10% on kiln sites compared to the control. Charcoal making kiln spots increased available soil phosphorus by 112% compared to the adjacent non-kiln sites. The Bray- P was strongly and significantly (P\0.05) correlated (r = 0.75) with soil pH. We conclude that integrating A. decurrens-based agroforestry practices would improve livelihoods by restoring degraded lands, improving income generation and carbon sequestration

Short term fallow and partitioning effects of green manures on wheat systems in East African highlands

Soil fertility depletion is a major constraint of smallholder farming in sub-Saharan Africa. We tested the aftereffects of green manures, namely vetch (Vicia sativa L.), lupin (Lupinus polyphyllus L.), and lablab (Lablab purpureus L.) incorporated into the soil compared to three fertilizer levels (0/0, 23/0, and 78/20 kg N/P h

The impact of water hyacinth biochar on maize growth and soil properties: The influence of pyrolysis temperature

Introduction: Options for managing water hyacinths (WHs) include converting the biomass into biochar for soil amendment. However, less has been known about the impact of WH‐based biochar developed in varying pyrolysis temperatures on plant growth and soil qualities. Materials and Methods: A pot experiment was undertaken in a factorial combination of WH biochars (WHBs) developed at three temperatures (350°C, 550°C and 750°C) and two application rates (5 and 20 t ha−1), plus a control without biochar. Maize was grown as a test crop for 2 months under natural conditions. Results: Our study showed that applying WHB developed between 350°C and 750°C at 20 t ha−1 increased maize shoot and root dry biomass by 47.7% to 17.6% and 78.4% to 54.1%, respectively. Nevertheless, raising the biochar pyrolysis temperature decreased maize growth, whereas increasing the application rate displayed a positive effect. The application of WHB generated at 350°C and 550°C at 20 t ha−1 resulted in significant improvements in soil total nitrogen (17.9% to 25%), cation exchange capacity (27.3% to 20.2%), and ammonium‐nitrogen (60.7% to 59.6%), respectively, over the control. Additionally, applying WHB produced from 350°C to 750°C at 20 t ha−1 enhanced soil carbon by 38.5%–56.3%, compared to the control. Conversely, applying biochar produced at 750°C resulted in higher soil pH (6.3 ± 0.103), electrical conductivity (0.23 ± 0.01 dSm−1) and available phosphorus (21.8 ± 2.53 mg kg−1). Conclusion: WHBs developed at temperatures of 350°C and 550°C with an application rate of 20 t ha−1 were found to be optimal for growing maize and improving soil characteristics. Our study concludes that pyrolysis temperature significantly governs the effectiveness of biochar produced from a specific biomass source

Sustainable weed management and soil enrichment with water hyacinth composting and mineral fertilizer integration

Composting water hyacinth (Eichhornia crassipes) presents a promising approach for managing the weed and the aquatic environment while increasing agricultural production and soil fertility. However, limited research reported on the impact of water hyacinth compost on soil properties and crop production under field conditions. This study aimed to evaluate impact of water hyacinth compost and its combined application with mineral fertilizer on soil properties and crop production. Before field experiments, the compost's phytotoxicity was assessed through bioassays, confirming it was safe for agricultural use with a seed germination index exceeding 80 %. Field trials were conducted using a factorial design with four application rates of water hyacinth compost (0, 8, 16, and 24 t ha-1) and three rates of the recommended mineral fertilizer for teff production (0/0, 40/23, and 80/46 kg N/P2O5 ha-1). The results indicated that compared to the control group, applying water hyacinth compost increased soil pH by up to 0.69 units and reduced bulk density by 10.3 %. Soil organic carbon, total nitrogen, available phosphorus, cation exchange capacity, and exchangeable potassium increased by 24.3 %, 28.6 %, 80.2 %, 26.2 %, and 112.7 %, respectively. Furthermore, exchangeable acidity and aluminum were reduced by 72.5 % and 78.6 %, respectively. The maximum grain yield (1826 kg ha-1) and total biomass (8020 kg ha-1) of teff were achieved by applying 24 t ha-1 of water hyacinth compost coupled with the full rate of mineral fertilizer. However, compared to adding only full fertilizer, the grain yield that resulted from applying water hyacinth compost at 16 and 24 t ha-1 along with half of the suggested mineral fertilizer was superior. This implies that water hyacinth compost could substitute 50 % of the mineral fertilizer required. In conclusion, composting water hyacinth offers a dual benefit of weed management and soil enrichment. This could be a sustainable strategy to mitigate weed proliferation while improving soil quality and crop production

Efficacy of Carraguard®-Based Microbicides In Vivo Despite Variable In Vitro Activity

Anti-HIV microbicides are being investigated in clinical trials and understanding how promising strategies work, coincident with demonstrating efficacy in vivo, is central to advancing new generation microbicides. We evaluated Carraguard® and a new generation Carraguard-based formulation containing the non-nucleoside reverse transcriptase inhibitor (NNRTI) MIV-150 (PC-817). Since dendritic cells (DCs) are believed to be important in HIV transmission, the formulations were tested for the ability to limit DC-driven infection in vitro versus vaginal infection of macaques with RT-SHIV (SIVmac239 bearing HIV reverse transcriptase). Carraguard showed limited activity against cell-free and mature DC-driven RT-SHIV infections and, surprisingly, low doses of Carraguard enhanced infection. However, nanomolar amounts of MIV-150 overcame enhancement and blocked DC-transmitted infection. In contrast, Carraguard impeded infection of immature DCs coincident with DC maturation. Despite this variable activity in vitro, Carraguard and PC-817 prevented vaginal transmission of RT-SHIV when applied 30 min prior to challenge. PC-817 appeared no more effective than Carraguard in vivo, due to the limited activity of a single dose of MIV-150 and the dominant barrier effect of Carraguard. However, 3 doses of MIV-150 in placebo gel at and around challenge limited vaginal infection, demonstrating the potential activity of a topically applied NNRTI. These data demonstrate discordant observations when comparing in vitro and in vivo efficacy of Carraguard-based microbicides, highlighting the difficulties in testing putative anti-viral strategies in vitro to predict in vivo activity. This work also underscores the potential of Carraguard-based formulations for the delivery of anti-viral drugs to prevent vaginal HIV infection