Improve Phosphorus Availability Research Articles

Moderately deep banding of phosphorus enhanced winter wheat yield by improving phosphorus availability, root spatial distribution, and growth

Applying deep banding fertilizer is considered an effective strategy to improve grain yield and optimize fertilization management. However, the effect of P fertilizer application depth on P availability in the soil and the key mechanisms enabling the banding of P application to increase yield and efficiency under different soil layers, particularly in the field, remain unclear. We designed a field experiment using winter wheat (Triticum aestivum L.) to explore the effects of different P fertilizer placement depths of 8 cm (DP8), 16 cm (DP16), and 24 cm (DP24) on P availability and root spatial distribution. When compared with No P (no P fertilizer), the available P content of DP8, DP16, and DP24 in the corresponding soil layer increased by 30.0%, 82.4%, and 150.7%, respectively, in the two seasons. This increase in P availability caused a significant increase in the inorganic P (Pi) fractions of dicalcium phosphorus (Ca2-P), octacalcium phosphorus (Ca8-P), aluminum phosphorus (Al-P), and iron phosphorus (Fe-P), particularly in the 8–16 cm soil layer. Based on the increase in available P, especially the accumulation of Pi, in different soil layers, the root length density, root surface area density, and root activity were improved. The deeper P application treatments (DP16 and DP24) obtained 9.6–25.2% and 80.1–209.5% higher P uptake and phosphorus-use efficiency, respectively, compared with those of the traditional fertilization depth treatment (DP8). The grain yield increased by 17.0–19.7% and 5.2–8.1% in the DP16 and DP24 treatments, respectively, compared to that in the DP8 treatment. Additionally, the deep banding P application improved the aboveground biomass and harvest index, particularly in DP16, with an increase of 11.8–16.3% and 2.9–4.6% compared with that after DP8 treatment, respectively. Consequently, deep banding P application improved soil P availability and plant growth in the sub-humid area, especially when provided at a depth of 16 cm. Similarly, understanding this mechanism and the interaction between different deep banding P application depths with crops provides a practical reference for optimizing fertilizer management.

Co-application of triple super phosphate and chicken litter biochar improves phosphorus availability of mineral tropical acid soils to reduce water pollution

Co-application of triple super phosphate and chicken litter biochar improves phosphorus availability of mineral tropical acid soils to reduce water pollution

Acaulospora as the Dominant Arbuscular Mycorrhizal Fungi in Organic Lowland Rice Paddies Improves Phosphorus Availability in Soils

Flooding in rainfed lowlands greatly impairs the mutualistic relationship between indigenous arbuscular mycorrhizal fungi (AMF) and rice. In flooded soils, root colonization by AMF is arrested, but some AMF genera, defined as the core AMF, remain present. However, the core AMF in rainfed lowlands and their symbiotic roles remain unknown. Here, we showed that Acaulospora fungi were the core AMF in rice seedling roots of the Sangyod Muang Phatthalung (SMP) landrace rice variety grown in non-flooded and flooded paddy soils. Subsequently, indigenous Acaulospora spores were propagated by trap cultures using maize as the host plants. Therefore, to clarify the roles of cultured Acaulospora spores in a symbiotic partnership, the model japonica rice variety Nipponbare was grown in sterile soil inoculated with Acaulospora spores, and recolonized with a native microbial filtrate from the organic rice paddy soil. Our data demonstrated that the inoculation of Acaulospora spores in well-drained soil under a nutrient-sufficient condition for six weeks enabled 70 percent of the rice roots to be colonized by the fungi, leading to higher phosphate (Pi) accumulation in the mycorrhizal roots. Unexpectedly, the growth of rice seedlings was significantly suppressed by inoculation while photosynthetic parameters such as fractions of incoming light energy and relative chlorophyll content were unaltered. In the soil, the Acaulospora fungi increased soil phosphorus (P) availability by enhancing the secretion of acid phosphatase in the mycorrhizal roots. The findings of this work elucidate the symbiotic roles of the dominant Acaulospora fungi from lowland rice paddies.

Agronomic and financial benefits of direct Minjingu phosphate rock use in acidic humic nitisols of Upper Eastern Kenya

A major constraint to crop production in Sub-Saharan Africa is nutrient deficiency, especially phosphorus (P) deficiency. Phosphorus plays a crucial role in photosynthesis but is usually deficient in acidic soils since it is converted to less available forms, affecting crop yields. There is a need to improve phosphorus availability to crops for maximum production. This study assessed Minjingu phosphate rock fertilizer's impact on maize yields, soil chemical composition, and cost-effectiveness in acidic humic nitisols of Tharaka Nithi County, Upper Eastern Kenya. A field experiment in a randomized complete block design (RCBD) was set during long rains (SR2017) and Short rains (LR2018) seasons. The treatments were Minjingu phosphate rock, manure, Tithonia diversifolia, Minjingu phosphate rock + manure, Tithonia diversifolia + Minjingu phosphate rock, Calcium Ammonium Nitrate (CAN) + Triple Superphosphate (TSP), and a control. Soil samples were collected at a depth of 0–20 cm before and at the end of the experiment for pH, P-sorption, and other soil nutrient determinations. Other auxiliary data collected included labor and input costs besides output prices. The CAN+TSP treatment had significantly higher grain yields (6.86 Mg ha-1), while Minjingu phosphate rock on its own had the second-lowest than the control treatment (3.0 Mg ha-1). Also, a similar trend in the stover yields was observed. Minjingu phosphate rock combined with either manure or Tithonia diversifolia led to a significant increase (over 100%) in the phosphorous levels. Sole application of Minjingu phosphate rock increased soil iron levels while magnesium, copper, and zinc levels decreased significantly. Other than the control, all treatments significantly lowered the P-sorption levels. However, CAN+TSP had the highest P-sorption (913 mg kg−1)while Tithonia diversifolia had the lowest (744 mg kg−1). During the LR2018 season, all treatments reached a break-even point, and the net benefit was significantly higher at P < 0.05. Conclusively, the use of phosphate rock, either solely or in combination with organic elements, improved yields, soil chemical composition, P-sorption and was very cost-effective.

Optimisation of Charcoal and Sago (Metroxylon sagu) Bark Ash to Improve Phosphorus Availability in Acidic Soils

Soil acidity is an important soil factor affecting crop growth and development. This ultimately limits crop productivity and the profitability of farmers. Soil acidity increases the toxicity of Al, Fe, H, and Mn. The abundance of Al and Fe ions in weathered soils has been implicated in P fixation. To date, limited research has attempted to unravel the use of charcoal with the incorporation of sago (Metroxylon sagu) bark ash to reduce P fixation. Therefore, an incubation study was conducted in the Soil Science Laboratory of Universiti Putra Malaysia Bintulu Sarawak Campus, Malaysia for 90 days to determine the optimum amounts of charcoal and sago bark ash that could be used to improve the P availability of a mineral acidic soil. Charcoal and sago bark ash rates varied by 25%, whereas Egypt rock phosphate (ERP) rate was fixed at 100% of the recommendation rate. Soil available P was determined using the Mehlich 1 method, soil total P was extracted using the aqua regia method, and inorganic P was fractionated using the sequential extraction method based on its relative solubility. Other selected soil chemical properties were determined using standard procedures. The results reveal that co-application of charcoal, regardless of rate, substantially increased soil total carbon. In addition, application of 75% sago bark ash increased soil pH and at the same time, it reduced exchangeable acidity, Al3+, and Fe2+. Additionally, amending acidic soils with both charcoal and sago bark ash positively enhanced the availability of K, Ca, Mg, and Na. Although there was no significant improvement in soil Mehlich-P with or without charcoal and sago bark ash, the application of these amendments altered inorganic P fractions in the soil. Calcium-bound phosphorus was more pronounced compared with Al-P and Fe-P for the soil with ERP, charcoal, and sago bark ash. The findings of this study suggest that as soil pH decreases, P fixation by Al and Fe can be minimised using charcoal and sago bark ash. This is because of the alkalinity of sago bark ash and the high affinity of charcoal for Al and Fe ions to impede Al and Fe hydrolysis to produce more H+. Thus, the optimum rates of charcoal and sago bark ash to increase P availability are 75% sago bark ash with 75%, 50%, and 25% charcoal because these rates significantly reduced soil exchangeable acidity, Al3+, and Fe2+.

Agronomic and Financial Benefits of Phosphate Rock Use in Acidic Soils of Upper Eastern Kenya

A major constraint to crop production in Sub-Saharan Africa is nutrient deficiency, especially phosphorus deficiency. Phosphorus plays a crucial role in photosynthesis but is usually deficient in acidic soils since it is converted to less available forms, affecting crop yields. There is a need to improve phosphorus availability to crops for maximum production. This study assessed the impact of phosphate rock fertilizer application on maize yields, soil chemical composition, and cost-effectiveness in Tharaka Nithi County, Upper Eastern Kenya. We set a field experiment in a randomized complete block design (RCBD) during long rains (SR2017) and Short rains (LR2018) seasons. The treatments were phosphate rock + manure, Tithonia diversifolia + phosphate rock, Calcium Ammonium Nitrate (CAN) + Triple Superphosphate (TSP), and a control. Soil samples were collected at a depth of 0-20 cm before and at the end of the experiment for pH, P-sorption, and other soil nutrients determinations. Other auxiliary data collected included labor and input costs besides output prices. The CAN+TSP treatment had significantly higher grain yields, while phosphate rock on its own had the second-lowest than the control treatment (p<0.05). We also observed a similar trend in the stover yields. Phosphate rock combined with either manure or Tithonia diversifolia led to a significant (p<0.05) increase in the phosphorous levels. Sole application of organics increased soil sodium and calcium while iron levels decreased. Other than the control, all treatments significantly lowered the p-sorption levels. However, CAN+TSP had the highest p-sorption while Tithonia diversifolia had the lowest. During the LR2018 season, a break-even point was arrived at with all the treatments, and the net benefit was significantly higher at P<0.05. Conclusively, the use of phosphate rock, either solely or in combination with organic elements, was found to improve yields, soil chemical composition, P-sorption, and very cost-effective.

Insight into the mechanisms of insoluble phosphate transformation driven by the interactions of compound microbes during composting.

Phosphate-solubilizing (PS) microbes are important to improve phosphorus availability and transformation of insoluble phosphate, e.g., rock phosphate (RP). The use of phosphate solubilizing bacteria (PSB) as inoculants have been proposed as an alternative to increase phosphate availability in RP and composting fertilizers. In this study, the effect of compound PSB coinoculation and single-strain inoculation on the transformation of insoluble phosphate were compared in a liquid medium incubation and RP-enriched composting. The goal of this study was to understand the possible mechanisms of insoluble phosphate transformation driven by the interactions of compound PS microbes during composting. The correlations between organic acids production, P-solubilization capacity and bacterial community with PSB inoculation were investigated in the RP-enriched composting by redundancy analysis (RDA) and structural equation models (SEM). Results showed that both single-strain and compound PSB inoculants had a high P-solubilization capacity in medium, but the proportion of Olsen P to total P in composts with inoculating compound PS microbes was 7% higher than that with single strain. PS inoculants could secrete different organic acids and lactic was the most abundant. However, RDA and SEM suggested that oxalic might play an important role on PS activity, inducing RP solubilization by changing pH during composting. Interaction between compound microbes could intensify the acidolysis process for insoluble P transformation compared to the single strain. Our findings help to understand the roles of complex microbial inoculants and regulate P availability of insoluble phosphate for the agricultural purposes.

Maize straw and its biochar affect phosphorus distribution in soil aggregates and are beneficial for improving phosphorus availability along the soil profile

AbstractReturn of crop straw and its biochar to the agricultural field decreases pressure on phosphorus (P) resources and reduces leaching and P runoff. We conducted a 5‐year field trial from 2013 to 2017 to study the capability of maize straw and its biochar to retain soil P, which was quantified by investigating the distribution of P fractions in the soil profile (0–100 cm) and soil aggregates of different grain sizes. The impact of soil treatments with nitrogen‐phosphorus‐potassium (NPK) fertiliser alone or combined with biochar or maize straw were examined. We found that maize straw and its biochar increased soil aggregate stability, which showed an increase in mean weight diameter, geometric mean diameter, and aggregates with diameter &gt; 250 μm. Maize straw and its biochar promoted both inorganic (dicalcium phosphate dehydrate [Ca2‐P], octocalcium phosphate [Ca8‐P], aluminium phosphate [Al‐P], iron phosphate [Fe‐P], hydroxyapatite [Ca10‐P], and occluded phosphate [O‐P]) and organic (labile organic phosphorus, LOP, and moderately labile organic phosphorus, MLOP) P accumulation and stabilization in soil aggregates, especially in small macroaggregates of 250–2000 μm. Total phosphorus (TP), Ca8‐P, Fe‐P, LOP, MLOP, moderately resistant organic phosphorus (MROP) and highly resistant organic phosphorus (HROP) were enhanced by maize straw and its biochar, whereas Ca2‐P and O‐P were decreased in the 0–20‐cm topsoil. We measured decreased TP, Fe‐P, O‐P and Ca10‐P in the 40–100‐cm soil layer following maize straw and biochar deposition, whereas higher Ca2‐P, Al‐P, MROP and HROP were obtained in maize straw‐supplemented soil relative to NPK fertiliser treatment in the 20–100‐cm soil layer. Thus, maize straw and its biochar can be used to effectively improve soil structure to support P retention and biochar has the potential to reduce P leaching from the soil profile.Highlights Maize straw and its biochar effectively improved soil structure to support P retention Inorganic and organic P fractions mainly accumulated in the small macroaggregate fraction Biochar has the potential to reduce P leaching in the soil profile

Role of endomycorrhizae, rhizobacteria and compost to improve phosphorus availability in onion

Role of endomycorrhizae, rhizobacteria and compost to improve phosphorus availability in onion

The effect of tillage systems on phosphorus distribution and forms in rhizosphere and non-rhizosphere soil under maize (Zea mays L.) in Northeast China

An appropriate tillage method must be implemented by maize growers to improve phosphorus dynamics in the soil in order to increase phosphorus uptake by plant. The objective of this study was to investigate the effects of tillage systems on phosphorus and its fractions in rhizosphere and non-rhizosphere soils under maize. An experimental field was established, with phosphate fertilizers applied to four treatment plots: continuous rotary tillage (CR), continuous no-tillage (CN), plowing-rotary tillage (PR), and plowing-no tillage (PN). Under the different tillage methods, the available P was increased in the non-rhizosphere region. However, the concentration of available P was reduced in the rhizosphere soil region. The soil available P decreased with the age of the crop until the maize reached physiological maturity. The non-rhizosphere region had 132.9%, 82.5%, 259.8%, and 148.4% more available P than the rhizosphere region under the CR, PR, CN, and PN treatments, respectively. The continuous no-tillage method (CN) improved the uptake of soil phosphate by maize. The concentrations of Ca2-P, Ca8-P, Fe-P, Al-P and O-P at the maturity stage were significantly lower than other seedling stages. However, there was no significant relationship between total P and the P fractions. Therefore, a continuous no-tillage method (CN) can be used by farmers to improve phosphorus availability for spring maize. Soil management practices minimizing soil disturbance can be used to impove phosphorus availability for maize roots, increase alkaline phosphatase activity in the rhizosphere soil and increase the abundance of different phosphorus fractions.

Effects of Various Ameliorants on pH, Phosphorus Availability and Soybean Production in Alfisols

Alfisols have inherent potential to increase Indonesia’s soybean production, however, alfisols also known for its low phosphorus availability. Field experiment using ameliorants consisting of quail manure, zeolites and rock phosphate was conducted to increase phosphorus (P) availability and soybean production. The aim of this study is to evaluate the effects of ameliorant combinations for improving phosphorus availability and its correlation to soybean production in alfisols. Randomized complete block design with single factor was used, with 9 combinations of ameliorants under study (P0 – P8). Obtained results showed that phosphorus availability is increased up to 72.6% and soybean yield upto 75.9%. Correlation of phosphorus availability and soybean production was significant (r = 0.854). Finally, the best treatment to increase phosphorus availability and soybean production is quail manure 2.5 t.ha-1 + rock phosphate 5 t.ha-1).

Reducing Acidity of Tropical Acid Soil to Improve Phosphorus Availability and Zea mays L. Productivity through Efficient Use of Chicken Litter Biochar and Triple Superphosphate

Phosphorus is a macronutrient which plays an important role in plant metabolism, growth, and development. However, in tropical acid soils, P fixation is high because of significant amounts of Al and Fe ions. Al and Fe ions can reduce diffusion of P into plant roots. Low absorption of P at initial growth of most plants causes stunting and slow growth of plant leaves. This process reduces photosynthesis. Chicken litter biochar (CLB) had been used on tropical acid soils to improve total P, available P, organic P, and inorganic fractions of P. Moreover, CLB is able to reduce exchangeable acidity, Fe, and Al ions in mineral acid soils because of the reactive surfaces of this organic amendment. However, there is dearth of information on the effects of the right combination of CLB and triple superphosphate (TSP) on the aforementioned soil chemical properties and crop productivity. To this end, the objectives of this study were to improve P: (i) Availability in a mineral acid soil and (ii) uptake, agronomic efficiency, and dry matter yield of Zea mays L. using the right amounts of TSP and CLB. Combinations of 75%, 50%, and 25% CLB (based on recommended 5 t ha−1) and TSP (based on recommended P fertilization for maize) were evaluated in a pot study. Selected soil chemical properties, maize plants nutrient uptake, growth variables, and dry matter yield were determined using standard measures. Results showed that 25% and 50% biochar of 5 t ha−1 with 75% TSP can increase soil P availability, recovery, agronomic use efficiency, and dry matter yield of maize plants. These optimum rates can also reduce P fixation by Al and Fe ions. Therefore, soil and maize productivity can be improved by using CLB (25% and 50% of 5 t ha−1) and TSP (75% of conventional rate) to increase nutrients availability especially P.

Sulfur, Na2-EDTA and their mixture effects on phosphorus release from cow bone char in P-poor sandy soil

Abstract The high cost and environmental problems related to the production of phosphate fertilizers as well as their excessive and continuous applications represent great challenges in modern agriculture. Therefore, we conducted an incubation experiment using sandy soil to evaluate the effects of elemental sulfur, disodium ethylene diamine tetra-acetic acid (Na2-EDTA) and their mixture with cow bone char as well as incubation periods on changes of phosphorus (P) availability, water soluble P, soil pH, electrical conductivity (EC), soluble calcium (Ca) and soluble sulfate (SO4). Applying sulfur (S), Na2EDTA and their mixture with cow bone char improved significantly phosphorus availability in soil, Olsen-P value increased from 7.65 mg kg−1 (control) to 12.20 mg kg−1 (cow bone char + sulfur), 12.80 mg kg−1 (cow bone char + Na2-EDTA) and 13.07 mg kg−1 (cow bone char + sulfur + Na2-EDTA) at the end of incubation periods While, cow bone char + sulfur + Na2-EDTA treatment lead Olsen-P to decline significantly with increasing incubation periods. Amending soil by sulfur with cow bone char treatment caused significant increase in the Olsen-P with increasing incubation periods. Cow bone char + sulfur and cow bone char + Na2-EDTA showed non-significant differences in Olsen-P. Because of the increase in phosphate fertilizer prices, the results of this study demonstrated the great potential of cow bone char usage which is a promising way to improve phosphorus availability in P-poor soil as well as being a clean alternative and renewable source of phosphate fertilizer. Consequently, we recommend utilizing cow bone char with sulfur as slow release fertilizer with time due to their low cost and it is a safe source of phosphorus in sustainable agriculture, rather than using Na2-EDTA due to its high price.

Changes in phytase activity, phosphorus and phytate contents during grain germination of barley (Hordeum vulgare L.) cultivars

Phytase activity, phosphorus and phytate contents in hydroponic fodder (up to 12 days of grain germination) of four Tunisian barley (Hordeum vulgare L.) cultivars (Arbi, Ardhaoui, Souihli, and Rihane) were studied. Barley cultivars differed significantly in their phytase activity (0.6–1.6 U/g), phosphorus (3.2–5.0 mg/g DM) and phytate (4.2–4.7 mg/g DM) contents. Phytase increased significantly up to 8 days of germination and decreased steadily thereafter. The phytase activity after 8 days of germination was increased up to tenfold in Arbi and Ardhaoui cultivars, eightfold in Souihli and fivefold in Rihane. The increase in phytase activity during germination was accompanied by a significant decrease in phytate content for all barley cultivars (reduced by 92–97%). The decrease in phytate content of sprouted barley by germination should improve phosphorus availability of the grain. Based on their phytase activity and phosphorus contents before germination, barley cultivars are ranked as Rihane > Ardhaoui > Souihli > Arbi. However, after germinating for 12 days the differences among varieties in phytase activity, phytate and phosphorus contents became non-significant. Further research is warranted to highlight the effect of germination on other nutritional attributes of hydroponic sprouted barley and its suitability as a feedstuff for farm animals.

English

A glasshouse experiment was conducted to evaluate the effect of composting coffee pulp with phosphate rock on phosphorus (P) availability for plant uptake. Coffee pulps composted with or without phosphate rock and Minjingu phosphate rock applied alone were evaluated as source of P for tomato growing on a Chromic Acrisol. All P sources were applied at varying rates of 0, 20, 40, 60, 80 and 100 mg P kg-1 and all other limiting nutrients were adjusted to recommend levels using industrial fertilizers and/or reagent grade laboratory salts. Phosphorus uptake of tomato plants receiving coffee pulp composted alone, Minjingu phosphate rock alone and coffee pulp composted with Minjingu phosphate rock increased 11, 13 and 18 times above the control. Observed P concentrations in tomato plants receiving external P sources were 23, 36%and 110% of the concentrations in control plants. Composting coffee pulp with Minjingu phosphate rock was concluded as a potential technique for improving phosphorus availability and uptake by tomato. Key words: phosphate rock, coffee pulp, phosphate rock enriched compost, tomato, phosphorus uptake.

Effect of different components of single superphosphate on organic matter degradation and maturity during pig manure composting

Single superphosphate (SSP) as an additive could improve phosphorus availability and reduce nitrogen loss for composts, but few studies have explored the influence of SSP on the transformation of carbon fractions in composting. The aim of this work was to assess the effect of different components of SSP, including calcium dihydrogen phosphate (CDP), calcium sulfate (CS) and free acid (FA) on organic matter degradation and maturity during pig manure composting. The results showed that CDP had significantly negative effects on the duration of thermophilic phase and organic matter degradation, but lengthened the curing phase for the transformation of organic matter. FA could intensify the inhibiting effect of CDP and postpone the biodegradation process of composting, but CS could buffer the effect of CDP on the degradation of organic carbon fractions by controlling pH. The study reveals the roles of different components of SSP to the transformation of organic carbon fractions, which lays a foundation for regulating the effects of chemical additives during composting. Regulating the content of CDP in SSP or applying SSP with other chemical additives to control the biotoxicity of excess phosphate on microbial activity should be concerned for complete and efficient composting in further study.

Amending triple superphosphate with chicken litter biochar improves phosphorus availability

The reaction of H2PO42- and HPO4- with Al and Fe in acid soils to form a precipitate reduces P availability. Chicken litter biochar has been used to improve soil P availability for maize production but with limited information on optimum rates of biochar and Triple Superphosphate (TSP) to increase P availability. This study determined the optimum amount of chicken litter biochar and TSP that could increase P availability. Different rates of chicken litter biochar and TSP were evaluated in an incubation study for 30, 60, and 90 days. Selected soil chemical properties before and after incubation were determined using standard procedures. Soil pH, total P, available P, and water soluble P increased in treatments with 75% and 50% biochar. Total acidity, exchangeable Al3+, and Fe2+ were significantly reduced by the chicken litter biochar. The chicken litter biochar also increased soil CEC and exchangeable cations (K, Ca, Mg and Na). The use of 75% and 50% of 5 t ha-1 biochar with 25% TSP of the existing recommendation can be used to increase P availability whilst minimizing soil Al and Fe content. This rates can be used to optimize chicken litter biochar and TSP use in acid soils for crop production especially maize and short term vegetables.

Adoption and Effect of Vetiver Grass (Vetiveria zizanioides) on soil Erosion in Somodo Watershed, South-Western Ethiopia

Soil erosion is an important cause of land degradation and consequent to soil fertility which reduces land productivity and production. This problem aggravates in developing countries like Ethiopia. To minimize this challenge, soil and water conservation with proper design is the first choice. The aim of this study was to assess the adoption and effect of Vetiver grass on soil erosion in Somodo watershed. Community mobilization was used to implement Vetiver grass on farm lands as bund stabilization and grass strip. Accordingly, more than 45 km (20%) of the watershed was covered by Vetiver grass on soil bund as bund stabilizing measure. The hedge was fully established within two years and formed averagely 36 cm raised terrace. The result of the study showed that within two years period about 36 cm soil was accumulated above the hedgerow. From mean annual soil deposition and average bulk density of the watershed, the mean annual soil loss was recorded 20.88 ton ha﹣1·year﹣1 in the absence of Vetiver hedge row as erosion barrier. In addition, field slope was reduced on average by 2.5% due to soil accumulated above Vetiver hedgerow. And phosphorus availability was found higher on the above hedgerow than below the hedge row while, exchangeable acidity was found less above the hedgerow than below the Vetiver hedgerow in the watershed which implies soil fertility improvement. The study recommends Vetiver hedgerow as an immediate mitigation measure for soil erosion on hill slopes and farm lands which can be implemented through community mobilization. Further study on how the Vetiver hedgerow improves phosphorus availability and decreases exchangeable acidity is also highly recommended.

ESPÉCIES DE UROCHLOA AFETAM DIFERENCIALMENTE A DISPONIBILIDADE DE FÓSFORO NO SOLO

Species of the genusUrochloaare promising as cover crops inno tillagesystemsas a strategy to improve phosphorus availability and recyclingin the soil. The objective of this work was to evaluate the effectiveness of ruzigrassspeciesin enhancing soil-Pavailability. The experiment was conducted in a greenhouse in pots with soil,with five treatments: Urochloa brizanthacv. Marandu, U. decumbens, U. humidicolaandU.ruziziensis, plus one control treatment without Urochloa cultivation. The Urochloaplants were grown in PVC potsof 12.6 L and 50 days after emergence,dry matteryield, P concentration andP accumulation were evaluated. The soil wasseparatedinto rhizosphere and bulk soil and used to determination of P availability, microbial P and pH. Urochloas increased phosphorus availabilityand soil pH. U. ruziziensisshowed higher initial growth, higher dry matter yieldand higher P uptake.There was no differencebetweenspecies as toP concentrations in the plantand microbial P insoil. U. ruziziensiswas the species resulting inthe lowest level of soil P available,similar toU. humidicola.Cultivation of Urochloas increases thesoilphosphorus availability and changesitschemical characteristics. Comparingthe species studied, U. ruziziensiswould bethe best to improve soil P availability and cycling inthesoil.

English

Understanding of phosphorus (P) retention and release mechanisms provides crucial information for the effective management of phosphorus to enhance crop production and sustain soil. In acidic soil, available phosphorus is fixed by aluminum and iron. To overcome this problem, soils are limed to fix aluminum and iron. But this practice is not economical for small scale farmers and also it is not environmentally friendly. This study was conducted to improve phosphorus availability using biochar produced from coffee husk and corn cob to fix aluminum and iron instead of phosphorus. Acidic soil samples were mixed with biochar applied at the rates of 0, 5, 10 and 15 t ha-1 and incubated in laboratory for 2 months at ambient temperature. The results showed significant effects (p<0.01) on selected soil chemical properties by increasing soil pH and reduced exchangeable acidity, exchangeable aluminum, and exchangeable iron in a way that enhanced the availability of phosphorus. Due to the incorporation of biochar the available P level increased to a level ranging 3.64±0.34 -23.21±0.07 mg/kg after an incubation period of 2 months and it increased by 84.3% available phosphorus when coffee husk biochar produced at 500°C temperature was applied at a rate of 15t/ha. Moreover, further field researches are needed to evaluate the effect of biochar on availability, the fate and uptake of available P in soil. Key words: Fixation, biochar, feedstock, acidic soil, pyrolysis temperature.