Application of phosphorus fertilizer can lead to changes in soil test P and increase both labile and non-labile phosphorus pools. Sequential fractionation showed that the labile (H2O-P and NaHCO3-P) fractions significantly (P < 0.05) increased with the addition of phosphorus fertilizer across all sites. Significant increase was observed in the non-labile (NaOH-P, HCl-P and Residual-P) fractions during the accumulation phase. During the depletion phase, when no further P was added, the accumulated P in the labile P fractions declined but not to the original level. The rates of P application, soil properties, soil test P methods used and time effect all had significant effects on soil test P changes in the extraction experiment. Mehlich-3 extracted the greatest amount of P from the two depths and Olsen-P was intermediate while the smallest amount was extracted with water. The pattern of the rate of change in extractable P with P addition for the 0 – 7.5 cm depth was not site dependent as the results obtained at the different sites were similar. / October 2016

Land application of biosolids as a soil fertility amendment is an alternative to traditional disposal methods. The influence of annual Alkaline Treated Biosolids (ATB) land application on phosphorus (P) dynamics in acidic soils needs to be better understood for more efficient P management. This study examines plant uptake, plant available, soil total phosphorus (P) content and potential P accumulation as a function of rate and frequency of application of an ATB amended to an agricultural soil over four years. The results suggest that applying high rates of ATB annually can increase the soil pH, Mehlich 3 and water extractable P, and crop P uptake in an acidic agricultural soil. No significant soil P accumulation was observed and P related environmental concerns were limited in this study. Potential soil P accumulation and higher P loss needs to be considered with annual high ATB rates application over a longer period study. / N/A

Increased adoption of compost bedded pack dairy barns (CBP), a relatively new housing and manure handling strategy, warrants study to facilitate proper use of CBP waste as a soil amendment. This study: 1) characterized in situ nutrient content and availability of CBP waste in terms of nitrogen (N) and phosphorus (P); 2) examined the decomposition of surface-applied CBP waste compared to an alternative processed solid waste amendment; 3) examined nutrient dynamics of incorporated CBP waste in high and low soil test phosphorus (STP) environments. Quick anaerobic mineralization assays revealed that bed management affects nutrient content and availability of CBP waste. A Fall surface-applied litter bag study showed that different particle sizes of CBP waste and a biosolid decomposed at similar rates. The biosolid had greater nutrient density and availability, but the decomposition was similar to CBP waste in terms of mineralization dynamics. Aerobic mineralization of CBP waste in high and low STP soils amended on a uniform P basis was compared with fresh manure. In general, CBP increased STP more and yielded more plant available P than fresh manure. These studies provide recommendations for CBP management and further study to ensure the proper land application of CBP waste.

The increase in soybean production in Manitoba has raised many questions about phosphorus management for achieving high yields of modern varieties. Soybean’s tolerance to seed-placed fertilizer and response to added fertilizer P were evaluated in a 28 site-year study, and the yield response to soil test P concentrations was evaluated in seven site-years, in a second study. Plant stand reduction caused by fertilizer toxicity when applied with the seed was rare, but was most likely in soils with medium to coarse texture or when seeding equipment lightly disturbed the soil, or provided little seed bed utilization. Severe plant stand reduction decreased seed yield in two site-years. Seed yield increase to P fertilization was rarely observed, regardless of fertilizer P rate, P placement or soil test P. In only one site-year there was a significant effect of fertilizer rate, where 45 and 90 kg P2O5 ha-1 increased yield by approximately 15%, compared to the control. Regardless of soil test P, seed yield response to soil P fertility was never observed. / October 2016

The inaccessibility and cost of soil testing reduce effectiveness of fertilizer use on small-scale subsistence farms, and inadequate funding promotes adoption of soil tests in developing countries with minimal validation. For example, Mehlich-I extraction of phosphorus (P) currently used extensively in Guatemala may not be suitable for its broad range of soils. At least four alternatives are available but are relatively untested [Bray 1, Mehlich III, Olsen and pressurized hot water (PHW)]. Pressurized hot water is relatively simple and inexpensive, but is not yet tested against other extraction methods under variable P or potassium (K) fertilization levels. To determine whether PHW-extracted nutrients could be used to predict maize yield, as nutrient content and uptake, soil, plant tissue and grain samples were obtained from a multiple-site field study and calibration studies were conducted using five rates of P and three rates of K on soils incubated without plants or cropped with maize in greenhouse and field conditions. In the multiple-site field study, maize yield related significantly to PHW-extractable P (r2=0.36) and to leaf P concentration (r2=0.23), but Mehlich I did not. In the two soils used in the greenhouse study, maize yield, vegetative P concentration and total P uptake by maize were predicted by PHW extractable P (R2=0.72, 0.75 and 0.90, respectively). In the field experiment, grain yield was not improved by P or K application, but P content of maize leaf tissue did relate significantly with PHW-extracted P (R2=0.40), but Mehlich I did not. There were no yield responses to K application in any experiment, but relationships defined between extractable K for all five K-extraction procedures and soil applied K were similarly significant. In comparing P extraction methods, PHW was as good as or better than Olsen, Bray 1 and Mehlich III for relating soil P extraction to the parameters measured in these experiments, and these four alternative extraction methods were consistently better than Mehlich I. Mehlich I extraction should be replaced by one of the four alternatives tested, and PHW is the least expensive and, thus, most viable for use in Guatemala soils.