Minimizing nutrient leaching from maize production systems in northern Ghana with one-time application of multi-nutrient fertilizer briquettes.

Nutrient losses through surface runoff and leaching from agricultural lands could have negative effects on surface water and groundwater resources in northern Ghana. Nutrient management strategies that synchronize nutrient uptake with availability will increase nutrient recovery efficiency and minimize nutrient losses to the environment. From field trials conducted at three locations in northern Ghana during the 2016 and 2017 farming seasons, we evaluated the effectiveness of one-time application of multi-nutrient fertilizer briquettes in minimizing nutrient leaching losses from maize production systems. We compared six fertilization strategies: (i) farmer practice (FP); (ii) NPK fertilizer briquettes applied at the recommended N, P, and K rates (100% briquette); (iii) 75% briquette; (iv) modified farmer practice (MFP) with granular N, P, and K sources applied at the recommended rate (100% MFP); (v) 75% MFP; and (vi) Control, with no fertilizer applied. Across all locations and both seasons, maize grain yield resulting from the treatments followed this order: 100% briquette >75% briquette = 100% MFP > 75% MFP > FP > control. Concentrations of leachate N from the two briquette treatments were consistently similar to background levels throughout the sampling periods, with the FP resulting in the greatest leachate N concentrations, followed by its modifications. There were no significant treatment effects on leachate P and K concentrations. Therefore, for environmental sustainability, the one-time application of multi-nutrient fertilizer briquettes could be an ideal fertilizer management strategy for maize production in northern Ghana. In addition to the environmental benefit of decreased nutrient leaching, one-time application of multi-nutrient fertilizer briquettes could provide significant agronomic benefits of increased yields from increased nutrient retention in the soil and improved nutrient utilization by the maize plants.

Retention-release characteristics of triclocarban and triclosan in biosolids, soils, and biosolids-amended soils.

Transport models that incorporate retention/release characteristics of organic compounds in soils and sediments typically assume that organic-carbon normalized partition coefficients (K(OC)) apply to all solid matrices and that the partitioning process is completely reversible. Partition coefficients (K(d)) (from which the K(OC) was calculated), and retention/release characteristics of triclocarban (TCC) and triclosan (TCS) in biosolids, soils, and biosolids-amended soils were determined. Four soils of different physicochemical properties amended with biosolids at 10 g/kg, together with unamended soils, and several biosolids were separately spiked with either [(14)C]TCC or [(14)C]TCS for the various determinations. The hysteresis coefficient values of the two compounds were consistently <1 in all three solid matrices, suggesting strong hysteresis. Multiple desorption steps (24 h each) over several days revealed incomplete desorption of the two compounds from all three solid matrices. The K(d) values determined in biosolids (log K(d) 3.34 +/- 0.13 for TCC and 3.76 +/- 0.39 for TCS) were greater than those determined in soils (log K(d) 1.71 +/- 0.09 for TCC and 2.25 +/- 0.26 for TCS) and biosolids-amended soils (log K(d)1.90 +/- 0.16 for TCC and 2.31 +/- 0.19 for TCS), however, the K(OC) values of all three solid matrices were similar (log K(OC) of 3.82 +/- 0.16 for TCC and 4.26 +/- 0.31 for TCS). Thus, it was concluded that a single or a narrow range of K(OC) values for TCC and TCS may be appropriate to describe retention of the compounds in soils and sediments. However, models that assume complete reversibility of the retention/release processes of the compounds in soils and sediments may not adequately describe the retention/release characteristics of the compounds in soils and sediments, especially when the chemicals are biosolids borne.

Characterization of adsorption and degradation of diuron in carbonatic and noncarbonatic soils.

The adsorption and degradation of the pesticide diuron in carbonatic and noncarbonatic soils were investigated to better understand the fate and transport of diuron in the environment. Batch adsorption experiments yielded isotherms that were well-described by the linear model. Adsorption coefficients normalized to soil organic carbon content (K(oc)) were lowest for carbonatic soils, averaging 259 +/- 48 (95% CI), 558 +/- 109, 973 +/- 156, and 2090 +/- 1054 for carbonatic soils, Histosols, Oxisols, and Spodosols, respectively. In addition, marl-carbonatic soils had much lower K(oc) values (197 +/- 27) than nonmarl-carbonatic soils. Diuron degradation data fit a first-order reaction kinetics model, yielding half-lives in soils ranging from 40 to 267 days. There was no significant difference between the average diuron degradation rate coefficients of each of the soil groups studied. Given the low adsorption capacity of carbonatic soils, it may be advisable to lower herbicide application rates in agricultural regions with carbonatic soils such as southern Florida to protect aquatic ecosystems and water quality.

Lability of drinking water treatment residuals (WTR) immobilized phosphorus: aging and pH effects.

Time constraints associated with conducting long-term (>20 yr) field experiments to test the stability of drinking water treatment residuals (WTR) sorbed phosphorus (P) inhibit improved understanding of the fate of sorbed P in soils when important soil properties (e.g., pH) change. We used artificially aged samples to evaluate aging and pH effects on lability of WTR-immobilized P. Artificial aging was achieved through incubation at elevated temperatures (46 or 70 degrees C) for 4.5 yr, and through repeated wetting and drying for 2 yr. Using a modified isotopic ((32)P) dilution technique, coupled with a stepwise acidification procedure, we monitored changes in labile P concentrations over time. This technique enabled evaluation of the effect of pH on the lability of WTR-immobilized P. Within the pH range of 4 to 7, WTR amendment, coupled with artificial aging, ultimately reduced labile P concentrations by > or = 75% relative to the control (no-WTR) samples. Soil samples with different physicochemical properties from two 7.5-yr-old, one-time WTR-amended field sites were utilized to validate the trends observed with the artificially aged samples. Despite the differences in physicochemical properties among the three (two field-aged and one artificially aged) soil samples, similar trends of aging and pH effects on lability of WTR-immobilized P were observed. Labile P concentrations of the WTR-amended field-aged samples of the two sites decreased 6 mo after WTR amendment and the reduction persisted for 7.5 yr, ultimately resulting in > or = 70% reduction, compared to the control plots. We conclude that WTR application is capable of reducing labile P concentration in P-impacted soils, doing so for a long time, and that within the commonly encountered range of pH values for agricultural soils WTR-immobilized P should be stable.

Long-term phosphorus immobilization by a drinking water treatment residual.

Excessive soluble P in runoff is a common cause of eutrophication in fresh waters. Evidence indicates that drinking water treatment residuals (WTRs) can reduce soluble P concentrations in P-impacted soils in the short term (days to weeks). The long-term (years) stability of WTR-immobilized P has been inferred, but validating field data are scarce. This research was undertaken at two Michigan field sites with a history of heavy manure applications to study the longevity of alum-based WTR (Al-WTR) effects on P solubility over time (7.5 yr). At both sites, amendment with Al-WTR reduced water-soluble P (WSP) concentration by >or=60% as compared to the control plots, and the Al-WTR-immobilized P (WTR-P) remained stable 7.5 yr after Al-WTR application. Rainfall simulation techniques were utilized to investigate P losses in runoff and leachate from surface soils of the field sites at 7.5 yr after Al-WTR application. At both sites, amendment with Al-WTR reduced dissolved P and bioavailable P (BAP) by >50% as compared to the control plots, showing that WTR-immobilized P remained nonlabile even 7.5 yr after Al-WTR amendment. Thus, WTR-immobilized P would not be expected to dissolve into runoff and leachate to contaminate surface waters or groundwater. Even if WTR-P is lost via erosion to surface waters, the bioavailability of the immobilized P should be minimal and should have negligible effects on water quality. However, if the WTR particles are destroyed by extreme conditions, P loss to water could pose a eutrophication risk.