Darshani Kumaragamage

Phosphorus Mobilization from Manure-Amended and Unamended Alkaline Soils to Overlying Water during Simulated Flooding

Anaerobic soil conditions resulting from flooding often enhance release of phosphorus (P) to overlying water. Enhanced P release is well documented for flooded acidic soils; however, there is little information for flooded alkaline soils. We examined the effect of flooding and anaerobic conditions on P mobilization using 12 alkaline soils from Manitoba that were either unamended or amended with solid cattle manure. Pore water and floodwater were analyzed over 8 wk of simulated flooding for dissolved reactive P (DRP), Ca, Mg, Fe, and Mn. As expected, manured soils had significantly greater pore and floodwater DRP concentrations than unamended. Flooding increased pore water DRP concentrations significantly in all soils and treatments except one manured clay in which concentrations increased initially and then decreased. Floodwater DRP concentrations increased significantly by two- to 15-fold in 10 soils regardless of amendment treatment but remained relatively stable in the two soils with greatest clay content. Phosphorus release at the onset of flooding was associated with the release of Ca, Mg, and Mn, suggesting that P release may be controlled by the dissolution of Mg and Ca phosphates and reductive dissolution of Mn phosphates. Thereafter, P release was associated with release of Fe, suggesting the reductive dissolution of Fe phosphates. Differences in pore water and floodwater DRP concentrations among soils and amendment treatments and the high variability in P mobilization from pore water to floodwater among soils indicate the need to further investigate chemical reactions responsible for P release and mobility under anaerobic conditions.

Systematic Approach to Diagnosing Fertility Problems in Soils of Sri Lanka

Diagnosing soil fertility problems is essential to supply plant nutrients in a complete and a balanced manner. We evaluated and validated a systematic approach of diagnosing fertility problems based on optimum values established elsewhere for 32 cultivated soils representing different agroecological zones of Sri Lanka. Soils were analyzed for available ammonium nitrogen (NH4−N), phosphorus (P), potassium (K), copper (Cu), iron (Fe), manganese (Mn), zinc (Zn), calcium (Ca), magnesium (Mg), sulfate – sulfur (SO4−S), and boron (B) concentrations, and based upon these analyses we calculated nutrient application rates. Molybdenum (Mo) and calcium carbonate (CaCO3) application rates were calculated based on the active acidity of soils, while those of P, K, S, Cu, Mn, Zn, and B were adjusted considering their respective fixation capacities. An optimum treatment providing nutrients at “optimum” concentrations was validated in the greenhouse using sorghum as the indicator plant. The optimum treatment was compared with 13 other treatments of individual nutrients or CaCO3 consisting of either omissions (optimum treatment minus a particular nutrient) or additions (optimum treatment plus a particular nutrient). The treatments were replicated four times. All soils were deficient in N and B, while most (30 out of 32) were deficient in P, K, and S. Deficiencies of Ca, Mg, Cu, Zn, and Mn were less common (<75% of soils), while all soils had sufficient Fe. Fixation abilities for nutrients varied widely. Significant (P < 0.05) yield reductions in minus treatments were observed for N and P in 100% of soils; K, S, and CaCO3 in 50–60% of soils; Ca in 38% of soils; and Mg, Cu, Zn, B, and Mo in less than 20% of soils. Plus treatments gave significant yield reductions occasionally, probably due to toxicities and nutrient imbalances. In 11 soils identified as deficient in K, Ca, and B, dry-matter yields were significantly lower in the optimum treatment than the respective minus treatment, indicating that bringing the nutrient concentration up to the optimum level reduced the yields, signifying the need to validate the optimum levels used for these nutrients. This approach of combining soil analyses and fixation studies could be successfully used to diagnose fertility problems; however, the results indicate the need to adjust the “optimum” concentrations of K, Ca, and B before using them in a fertilizer recommendation program.

Impact of manure phosphorus fractions on phosphorus loss from manured soils after incubation.

The risk of P loss from manured soils is more related to P fractions than total P concentration in manure. This study examined the impact of manure P fractions on P losses from liquid swine manure- (LSM), solid cattle manure- (SCM), and monoammonium phosphate- (MAP) treated soils. Manure or fertilizer was applied at 50 mg P kg soil, mixed, and incubated at 20°C for 6 wk to simulate the interaction between applied P and soil when P is applied well in advance of a high risk period for runoff. Phosphorus fractions in manure were determined using the modified Hedley fractionation scheme. We used simulated rainfall (75 mm h⁻¹ for 1 h) to quantify P losses in runoff from two soils (sand and clay loam). The proportion of total labile P (total P in water+NaHCO fractions) in manure was significantly greater in LSM (70%) than SCM (44%). Mean dissolved reactive P (DRP) load in runoff over 60 min was greatest from MAP-treated soil (18.1 mg tray⁻¹), followed by LSM- (14.0 mg tray⁻¹) and SCM- (11.0 mg tray⁻¹) treated soils, all of which were greater than mean DRP load from the check (5.2 mg tray⁻¹). Total labile P (water+NaHCO) in manure was a more accurate predictor of runoff DRP loads than water extractable P, alone, for these two soils. Therefore, NaHCO extraction of manure P may be a useful tool for managing the risk of manure P runoff losses when manure is applied outside a high risk period for runoff loss.

Profiling undergraduate soil science education in Canada: Status and projected trends

Abstract: Global declines in postsecondary enrollment in soil science programs over the last several decades have been mainly attributed to an overemphasis on the connection with agronomy and production agriculture but recent enrollment increases in the USA suggest change is afoot. To determine if similar trends are occurring in Canada, we inventoried undergraduate soil science course offerings at postsecondary institutions and conducted a survey to assess the status and projected trends in soil science education. We found that 64% of universities and 37% of colleges offer undergraduate soil science courses as part of degrees or diplomas in which knowledge of soil science is important (e.g., agriculture and resource management). In Canada, there are 149 undergraduate soil science courses taught in universities and 58 at colleges. On average, there are 3.2 courses taught at each university and 1.9 at each college that offer soil science courses. Soil science programs at the University of British Columbia, University of Saskatchewan, and University of Manitoba offer between eight and nine soil science courses and represent 17.4% of the national total. Enrollments in all courses across the country are projected to be steady with some anticipated growth, trends that are consistent with those reported in the USA and the Netherlands.

Phosphorus fractions in solid and liquid separates of Swine slurry separated using different technologies.

Solid-liquid separation is a manure management option whereby P-rich solid is separated from N-rich liquid, allowing the separated liquid to be used as a fertilizer without oversupplying P. Little information is available on how the different P fractions in manures are partitioned to solid and liquid during separation. We examined the distribution of various P fractions in liquid and solid separates of swine manure, separated using different techniques, to gain information useful for making choices regarding the optimum use of manure separates. Samples of raw manure (RM) and their separated solid (SS) and liquid (SL) were obtained using three different separation techniques: (i) centrifugation without flocculant (CNF), (ii) centrifugation with a flocculant (CFL), and (iii) rotary press with a flocculant (RFL). These were subsequently analyzed for P using a modified Hedley fractionation scheme. Only a small proportion of RM, ranging from 5 to 12%, was recovered in SS, an advantage if SS is to be transported off-site. Concentrations of molybdate-reactive P and total P in all P fractions were less in SL than in the corresponding RM on a fresh-weight basis. The separation index (percentage partitioned to SS) for total labile P (water-extractable + NaHCO-extractable P) was 63, 81, and 75% for CNF, CFL, and RFL, respectively. The proportion of total P in labile form was significantly lower in SL than in RM. Therefore, using SL as a fertilizer instead of RM may help to avoid excessive buildup of soil test P with manure applications.

Predicting Phosphorus Release from Anaerobic, Alkaline, Flooded Soils

Anaerobic conditions induced by prolonged flooding often lead to an enhanced release of phosphorus (P) to floodwater; however, this effect is not consistent across soils. This study aimed to develop an index to predict P release potential from alkaline soils under simulated flooded conditions. Twelve unamended or manure-amended surface soils from Manitoba were analyzed for basic soil properties, Olsen P (Ols-P), Mehlich-3 extractable total P (M3P), Mehlich-3 extractable molybdate-reactive P (M3P), water extractable P (WEP), soil P fractions, single-point P sorption capacity (P), and Mehlich-3 extractable Ca (M3Ca), and Mg (M3Mg). Degree of P saturation (DPS) was calculated using Ols-P, M3P or M3P as the intensity factor, and an estimated adsorption maximum based on either P or M3Ca + M3Mg as the capacity factor. To develop the model, we used the previously reported floodwater dissolved reactive P (DRP) concentration changes during 8 wk of flooding for the same unamended and manured soils. Relative changes in floodwater DRP concentration (DRP), calculated as the ratio of maximum to initial DRP concentration, ranged from 2 to 15 across ten of the soils, but were ≤1.5 in the two soils with the greatest clay content. Partial least squares analysis indicated that DPS3 calculated using M3P as the intensity factor and (2 × P) + M3P as the capacity factor with clay percentage can effectively predict DRP ( = 0.74). Results suggest that P release from a soil to floodwater may be predicted using simple and easily measurable soil properties measured before flooding, but validation with more soils is needed.

Fertilizer-induced phosphorus dynamics in alkaline-calcareous soils as influenced by soil chemical properties

Abstract: For proper fertility management, the influence of soil properties on phosphorus (P) dynamics with fertilizer application should be better understood. We examined the influence of soil chemical properties on P dynamics with the application of monoammonium phosphate (MAP) to alkaline-calcareous soils from Manitoba. Nonfertilized and MAP-fertilized soils (at 30 and 60 kg P ha-1) were incubated for 8 wk. At 2 wk intervals, we analyzed pore water samples for dissolved reactive P (DRP) concentration, and soil samples for Olsen P (OP) and Mehlich-3 P (M3P) concentrations. Change in pore water DRP concentration with fertilizer application varied from a slight decrease (-0.02 mg L-1) to a significant, large increase (3.1 mg L-1) and showed a significant, negative relationship with P sorption capacity. The increase in OP and M3P with fertilizer application was influenced by the rate of P applied, initial soil test P and P sorption capacity. The estimated mean OP and M3P to maintain pore water DRP concentration at 0.2 mg L-1 were 25 and 48 mg kg-1, respectively. Fertilizer application at the same rate resulted in a widely varying degree of P saturation (DPS) increment depending on soil properties, indicating the importance of monitoring DPS changes for sustainable fertilizer use.

Heavy-Metal Fractions in Solid and Liquid Separates of Swine Slurry Separated using Different Technologies.

Accumulation of metals is a concern with continuous application of swine slurry to agricultural soils. Solid-liquid separation is a promising approach for reducing phosphorus and total metal loadings with swine manure application to farmlands. However, very little work has been performed on the partitioning of different metal fractions in swine slurry to separated solids and liquids. This study examined the distribution of various metal fractions in raw manures (RM), their separated liquids (SL), and separated solids (SS). The three separation techniques used were centrifuge without flocculant (CNF), centrifuge with flocculant (CFL), and rotary press with flocculant (RFL). Concentrations of Cd, Cu, Zn, Ni, and Se in manure and separates were determined by a modified Spositos sequential chemical fractionation scheme to extract water-soluble, exchangeable, organically bound, carbonate-precipitated, and residual fractions. The greatest concentrations of metals were recovered in the residual fraction, with the organically bound and carbonate-precipitated concentrations much greater than water-soluble and exchangeable fractions. Separation index () (i.e., percentage partitioned to SS) ranged from 13 to 66%, 9 to 87%, 16 to 93%, and 23 to 96% for water-soluble, exchangeable, organically bound, and carbonate-precipitated fractions, respectively. The values in general, were significantly ( < 0.05) greater for flocculant-based separation techniques than for CNF. For organically bound and carbonate-precipitated fractions, the greatest was obtained with the RFL for most metals. Our results suggest that applying the SL from RFL separation would minimize metal loading to farmlands compared with SL from CNF and CFL techniques. However, further validation is required using more sources of manure and different flocculants.

Performance of an Optimized Nutrient Management Approach for Tomato in Central Sri Lanka

A systematic approach of fertilizer recommendation for tomato was evaluated in central Sri Lanka. An optimum (OPT) treatment was formulated based on soil analysis for available nutrients and nutrient-fixation capacities and tested with sorghum (Sorghum vulgaris L.) in a greenhouse and with tomato (Lycopersicon eculentum L.) in the field for four seasons. Soil analysis revealed deficient levels of nitrogen (N), phosphorus (P), potassium (K), sulfur (S), boron (B), and zinc (Zn) with high fixing capacities for P, K, S, and B. Greenhouse survey confirmed nutrient deficiencies except for Zn. A field study with 17 treatments including OPT showed significant main effects and interaction of fertilizer treatment and season for tomato yields and profit. The OPT providing 220 kg N, 160 kg P, 250 kg K, 50 kg S, and 1 kg B per ha often gave greater yields and profits than treatments with lower nutrient rates, but treatment providing N, P, and K at 150% of optimum was superior.

Response of Maize (Zea Mays L.) to Phosphorus Fertilizers in Two Alfisols with Contrasting Phosphorus Availabilities and Sorption Capacities

ABSTRACT Increase in phosphorus (P) availability with fertilizer addition is influenced by soil properties such as P sorption capacity. We investigated P availability changes and response of maize (Zea mays L) to four P fertilizers rates (0, 20, 30 and 40 kg ha−1) in a two-site field experiment, having soils of contrastingly different available P (2.9 and 22.1 mg kg−1) and P sorption capacities (171.9 and 54.2 mg kg−1). Increase in available P was significantly greater in the soil with higher available P but lower P sorption capacity, than in the other; however, yield responses were similar in the two soils. Fertilizer P rates of 30 and 40 kg ha−1 gave significantly greater maize yields than the unfertilized treatment in both soils. Results suggest the need to account for the P sorption capacity when deciding rates of P fertilizers to increase available P in soils.