High Soil Test Phosphorus Research Articles

Yield of yellow cooking onions is not affected by added phosphorous fertilizer in muck soils with high soil test phosphorus in Ontario

Excess phosphorus (P) loading has been identified as an important cause of poor water quality in Lake Simcoe. A small (~ 4%) but important source of P is the marshland that was developed for agriculture in and near the Holland Marsh. Applying the optimum rate of P fertilizer is an economical and environmentally friendly approach to crop management. In Ontario, P fertilizer recommendations are made based on the Olsen P soil test that is accredited by the Ontario Ministry of Agriculture, Food and Rural Affairs (OMAFRA). The current study was a response to concern about high application rates of P fertilizer and grower and industry suggestions that the recommended rates for P were too low. The marketable yield of yellow cooking onions was assessed in relation to different rates of P fertilizer in high organic matter (muck) soils. Organic matter ranged from 38- 86%. Small (6 site-years) and large-scale (21 site-years) field trials were conducted in the Holland Marsh area from 2009 to 2011 on muck soils that varied in pre-plant P (17 - 312 mg L-1). The study demonstrated that there was more plant-available P in the soil than was required for optimum yield in most fields, thus P fertilizer applications had no effect on marketable yield of the onions. These results supported the OMAFRA P recommendations for onion production on muck soils, especially for soil test P levels over 61 mg L-1 where a response to applied P is rated as ‘low, rare or no response’.

High Soil Test Phosphorus Effect on Corn Yield

Low corn prices have farmers scrutinizing their nutrient dollar return on investment (ROI). A recent University of Nebraska–Lincoln study examines phosphorus (P) application level ROI in continuous corn over six years. The most cost‐effective method of fertilizer P use proved to be a P‐replacement approach with the P rate equal to the P removed from the previous harvest. The research also found that maintaining soil P availability levels above 25 ppm (Bray‐1) wasn't justified. Earn 0.5 CEUs in Nutrient Management by reading this article and taking the quiz at www.certifiedcropadviser.org/education/classroom/classes/706.

High Soil Test Phosphorus Effect on Corn Yield

Core Ideas High soil test P levels are often recommended for high yield corn. Many states recommend a deficiency correction approach for P application. Application of P to replace removal in the previous harvest was marginally superior. Maintenance of Bray‐1 P at > 25 ppm was not justified. Phosphorus removal in crop harvest has increased as yields have increased. Fertilizer P use guidelines are based on calibrations often developed for much lower yield levels and may need recalibration. Corn yields may be greater with higher than recommended soil test P when springs are relatively wet and cool. Research was conducted across 12 irrigated and five rainfed site‐years in Nebraska with initial Bray‐1 P ≤ 11 mg kg–1 to evaluate P application strategies for yield and P uptake of continuous corn (Zea mays L.) with and without tillage. The fertilizer P treatments were maintained on the same plots and included: (i) no P applied (0P); (ii) P applied according to the University of Nebraska‐Lincoln deficiency correction recommendation (UNL_P); (iii) P applied to replace P removed in the previous harvest (Replace_P); (iv) Bray‐1 P increased and maintained at 25 mg kg–1 (Bray_25); and (v) Bray‐1 P increased and maintained at 35 mg kg–1 (Bray_35). Interactions of P practice with other factors were not significant indicating consistency of P practice effects across varied climate conditions near planting and plant emergence. Grain yield was 9.3% and 0.89 Mg ha–1 more with the P‐applied treatments compared with 0P. Grain yield was 3.3% more due to the additional 5.9 kg ha–1 yr–1 P applied with Replace_P compared with UNL_P. Grain yield did not differ for Replace‐P, Bray_25, and Bray_35. Plant P uptake was on average linearly increased by 0.27 kg kg–1 P applied. Fertilizer P application for continuous corn should be by Replace_P.

Assessment of uncertainty in soil test phosphorus using kriging techniques and sequential Gaussian simulation: implications for water quality management in southern Quebec

Missisquoi Bay, located in southern Quebec at the north-eastern extremity of Lake Champlain, is subject to eutrophication arising from excess nutrients, predominantly phosphorus (P), contributed by agricultural watersheds. Factors such as land use pattern, management practices, soil properties and geomorphology have an impact on soil P levels. Land patches under different management practices introduce a cyclic pattern, especially when fitting the variogram. Geostatistics procedures were used to model soil test phosphorus (STP) within the 11 km2 Castor Watershed in southern Quebec, Canada. An ordinary kriging (OK) method was used to estimate STP at unsampled points, but this had a smoothing effect, resulting in an underestimation of high values and overestimation of low values. Therefore, a more efficient technique was needed to draw predictions from the conditional probability distribution at the simulation grid nodes. A sequential Gaussian simulation (SGS) was adopted for this purpose, and used to create 50 equal probable realizations. Uncertainty was modelled using the E-type (mean) of the realizations, which ranged from 12.5 to 223 mg P kg–1 soil. The adequate spatial probability pattern for STP is a valuable criterion when seeking to delineate areas of high STP for site-specific best management practices (BMPs).

Field-scale variability of soil test phosphorus and other nutrients in grasslands under long-term agricultural managements

Field-scale variation of soil nutrients in grassland is becoming important because of the use of soil-nutrient information as a basis for policies such as the recently introduced EU Nitrates Directive. This study investigates the field-scale variability of soil-test phosphorus (STP) and other nutrients in two grasslands with a long-term history of poultry litter application. Two fields (field 1 for silage and field 2 for grazing pasture) were selected, and soil samples were collected based on 12 m by 12 m (field 1) and 15 m by 15 m (field 2) grids. Data were analysed using conventional statistics, geostatistics, and a geographic information system (GIS). In field 1, STP values ranged from 12.4 to 90 mg L–1 (average 38.5 mg L–1). In field 2, STP values ranged from 4.3 to 130.0 mg L–1 (average 21.4 mg L–1). Attention should be paid to long-term poultry application, as the average STP values in both fields were much greater than the recommended agronomic optimum STP status in Ireland of 8 mg L–1. Coefficient of variation values of soil nutrients in field 2 were much higher than those in field 1. Log-transformation and Box–Cox transformation were applied to achieve normality. Statistically significant (P < 0.01), positive correlations between P and other nutrients were found in both fields. Exponential and spherical models were fitted to the experimental variograms of STP in fields 1 and 2, respectively. Compared with the counterparts in field 1, soil nutrients in field 2 had larger ‘nugget-to-sill’ values, revealing that sheep grazing could weaken the spatial auto-correlation of soil nutrients. A grid of 60 m by 60 m was recommended for soil sampling in grassland, based on this study. High STP concentrations in field 1 were in the north-eastern side, which was related to uneven poultry litter application. Strong spatial similarity of low STP, magnesium, and pH values in their spatial distribution were found in field 2, confirming their strong statistical correlation.

Rainfall Sequence Effects on Phosphorus Loss in Surface Runoff from Pastures that Received Poultry Litter Application

Land application of poultry litter to pasture elevates the concentration of phosphorus in surface runoff, and it is becoming an increasing problem in sensitive water bodies. The objectives of this study were to assess the effects of soil test phosphorus (STP), surface application of poultry litter, rainfall/runoff sequences, and time after litter application on dissolved reactive phosphorus (DRP) in surface runoff from pasture in a greenhouse experiment using rainfall simulation. Treatment factors were poultry litter at a rate of 0.0 and 6.7 Mg ha-1, low and high STP, and three rainfall/runoff sequences (RRS). The latter refers to runoff-producing rainfall events starting from day 1, day 4, and day 7 after litter application. The study also included a rainfall simulation study of pasture field plots to investigate the effects of poultry litter and time after application on DRP in surface runoff, which was used to corroborate the greenhouse study. In both studies, runoff samples were taken at the end of 30 min of continuous runoff. Treatment effects on DRP concentrations in surface runoff were analyzed using ANOVA procedures using an alpha = 0.05. For the greenhouse study, poultry litter application, RRS, and time after litter application were found to have a highly significant effect on DRP concentration in surface runoff. Poultry litter had a significant effect on DRP concentrations in surface runoff until 18 days after litter application compared to the controls. Between 18 and 32 days after litter application, the effect on DRP became insignificant for any level of STP or rainfall sequence. A rainfall event without runoff reduced DRP concentration in the first surface runoff events by more than 50%. For the field plot study, DRP decreased rapidly with time, thereby corroborating the greenhouse study. The effect of poultry litter on DRP became statistically insignificant sometime between 35 and 161 days after application.

Potato Yield and Tuber Set as Affected by Phosphorus Fertilization

A 3 year field study on a loamy sand soil with medium to high soil test phosphorus (P) concentrations (25 to 33 mg kg−1 Bray P1) was conducted to evaluate the effect of P fertilizer rate, source, and timing, and starter nitrogen (N) rate on potato (Solanum tuberosum L. cv. Russet Burbank) yield, tuber size, tuber set, petiole P concentration, and P uptake and distribution within the plant. Nine fertilizer treatments compared banded P rates of 0, 37, 42, and 74 kg P ha−1, the P sources monoammonium phosphate (MAP) and diammonium phosphate (DAP), P banded at planting vs. split applications at planting and emergence, and starter N rates of 38 and 66 kg N ha−1. Phosphorus fertilizer application increased total tuber yield and yield of undersized tubers (tubers less than 85 g), but decreased the proportion of large-sized tubers (greater than 285 g). Due to the increases in small, unmarketable tubers, P fertilizer application did not have a significant effect on marketable tuber yield (tubers greater than 85 g). The total number of tubers per plant and the number of undersized tubers were also higher, and the number of large tubers was lower, when P was applied compared with the zero P control. Both the number and yield of undersized tubers increased as P application rate increased. Petiole P concentrations were generally consistent with the rate of P applied, but they varied by year in magnitude and their pattern through the season. Petiole P was positively correlated with the number of tubers per plant, but only correlated for 1 year with differences in total yield. Phosphorus application increased total P uptake due primarily to an increase in tuber P concentration. Increases in total uptake and tuber P increased as P application rate increased, but differences in uptake were small relative to the amounts of P applied. Phosphorus source and timing and starter N rate did not consistently affect tuber yield, number, or size, petiole or tuber P concentration, and P uptake. The results of this study indicate that P nutrition can play an important role in regulating tuber set.

Reduction of High Soil Test Phosphorus by Bermudagrass and Ryegrass–Bermudagrass following the Cessation of Broiler Litter Applications

Factors that contribute to high soil P in bermudagrass [Cynodon dactylon L. (Pers.)] pastures include continued use of broiler litter rich in P to meet forage N requirements and removal of hay in summer only. This study determined if harvesting annual ryegrass (Lolium multiflorum Lam.) in addition to bermudagrass would reduce surplus soil P, Cu, and Zn faster than bermudagrass alone after litter application ceased on a Ruston soil (fine‐loamy, siliceaous, semiactive, thermic Typic Paleudults). During a 3‐yr build‐up, ‘Coastal’ bermudagrass was fertilized with 0, 4.5, 9, 18, and 36 Mg ha−1 litter yr−1 During the drawdown phase, plots were split and half was overseeded with ryegrass in fall 2001, 2002, and 2003. Whole plots were fertilized with NH4NO3 in spring–summer to provide 268 kg ha−1 N yr−1. Forage yield and P uptake increased as antecedent litter rate increased, and were greater in ryegrass–bermudagrass than bermudagrass in 2002, but not 2003. At 9 Mg ha−1 litter, harvesting ryegrass in addition to bermudagrass increased P uptake by 10 to 55%, depending on study year. During the drawdown phase, soil Mehlich‐3 P (M3P) and water‐extractable P to 15‐cm depth decreased by as much as 50 and 70%, respectively. Soils analysis within each sampling date found no significant effect of forage system or its interaction with litter rate. Data for 9 Mg ha−1 litter rate indicated 2 yr of forage P removal decreased residual M3P to an acceptable agronomic level (<70 mg kg−1). The potential to decrease surplus soil P by ryegrass–bermudagrass hay harvests was greatest when rainfall was inadequate for optimum bermudagrass yield.

Impacts of Variable‐Rate Phosphorus Fertilization Based on Dense Grid Soil Sampling on Soil‐Test Phosphorus and Grain Yield of Corn and Soybean

Most agricultural fields have high soil‐test phosphorus (STP) variability. Variable‐rate (VR) technology facilitates application of different P rates over a field and could improve nutrient application and crop yield. Replicated strip trials (6–12 ha) were established at six Iowa fields and were evaluated during 4 yr to compare VR and fixed‐rate (FR) P fertilization for corn (Zea mays L.)–soybean (Glycine max L. Merr.) rotations. Fields had median Mehlich‐3 STP ≤ 20 mg P kg−1, although minimum and maximum values within each field were 4 to 18 and 22 to 62 mg P kg−1, respectively. Treatments replicated at least three times were a control, VR based on STP from grid sampling (0.06‐ to 0.08‐ha grids), and FR based on median STP. Treatments were applied with commercial spreaders and grain was harvested with combines equipped with yield monitors and global positioning systems (GPS). Phosphorus increased yield in 13 site‐years and application methods differed in 1 site‐year, when FR increased yield further. On average, VR applied 12.4% less P and reduced STP variability in five fields compared with FR. Semivariograms and SD showed that fertilization, especially VR, often reduced yield variability and seldom increased it. High STP variability at a small scale and P recommendations to maximize yield and buildup STP in low‐testing soils might explain a lack of yield differences between application methods. Although VR did not increase yield compared with FR, it managed P better and showed potential for reducing excess P loss from fields through reduced P application to high‐testing field areas.

Use of Drinking Water Treatment Residuals as a Potential Best Management Practice to Reduce Phosphorus Risk Index Scores

The P risk index system has been developed to identify agricultural fields vulnerable to P loss as a step toward protecting surface water. Because of their high Langmuir phosphorus adsorption maxima (P(max)), use of drinking water treatment residuals (WTRs) should be considered as a best management practice (BMP) to lower P risk index scores. This work discusses three WTR application methods that can be used to reduce P risk scores: (i) enhanced buffer strip, (ii) incorporation into a high soil test phosphorus (STP) soil, and (iii) co-blending with manure or biosolids. The relationship between WTR P(max) and reduction in P extractability and runoff P was investigated. In a simulated rainfall experiment, using a buffer strip enhanced with 20 Mg WTR ha(-1), runoff P was reduced by from 66.8 to 86.2% and reductions were related to the WTR P(max). When 25 g kg(-1) WTR was incorporated into a high STP soil of 315 mg kg(-1) determined using Mehlich-3 extraction, 0.01 M calcium chloride-extractable phosphorus (CaCl(2)-P) reductions ranged from 60.9 to 96.0% and were strongly (P < 0.01) related to WTR P(max). At a 100 g kg(-1) WTR addition, Mehlich 3-extractable P reductions ranged from 41.1 to 86.7% and were strongly (P < 0.01) related to WTR P(max). Co-blending WTR at 250 g kg(-1) to manure or biosolids reduced CaCl(2)-P by >75%. The WTR P(max) normalized across WTR application rates (P(max) x WTR application) was significantly related to reductions in CaCl(2)-P or STP. Using WTR as a P risk index modifying factor will promote effective use of WTR as a BMP to reduce P loss from agricultural land.

Effects of Nitrogen Fertilization on Phosphorus Uptake in Bermudagrass Forage Grown on High Soil-Test Phosphorus Sites

Common bermudagrass [Cynodon dactylon (L.) Pers.] was harvested from two producer sites (Latta and Stephens) with high soil-test P (286 and 153 ppm, respectively) to assess the effects of N fertilization on P uptake and potential removal in hay or silage. Ammonium nitrate was applied in split applications each year at rates totaling 0, 56, 112, 168, 224, 280, or 336 kg/ha of actual N. At the Stephens site in Yr 1, cumulative DM yield increased linearly (P<0.0001) with N fertilization rate. Mean concentrations of P in these forages declined linearly (P<0.0001) with N fertilization rate, but uptake of P still increased linearly (P=0.0004) with N fertilization, reaching a maximum of 30.0kg of P/ha. At the Latta site, mean yields of DM and uptake of P for Yr 1 and 2 increased linearly (P<0.0001) with N fertilization; the maximum uptake of P was 50.8kg of P/ha. At the Latta site, there was an interaction between concentrations of P in the forage and year (P=0.002). During Yr 1, there was no relationship (P>0.10) between concentration of P and N fertilization rate (overall mean = 0.40%), but concentrations of P declined in linear (P<0.0001) and quadratic (P=0.044) patterns from 0.59 to 0.44% during Yr 2. Uptake of P was generally improved with N fertilization, but potential P removal may be limited by reductions in the concentration of P in the forage at greater N fertilization rates.

Reduction of High Soil Test Phosphorus by Corn and Soybean Varieties

Soils with high levels of P can contribute to excess P in runoff and subsequently pollute the surface water. Excess P in the soil can be removed from the system by harvesting crops. The objectives of this study were to evaluate corn (Zea mays L.) P removal effects on soil P reduction, and to evaluate various corn hybrids and soybean [Glycine max (L.) Merr.] varieties for differences in grain P concentration and P removal. Soil with varying P levels as a result of annual or biennial beef cattle (Bos taurus) feedlot manure or compost application was cropped to corn for 4 yr without any P addition. In other studies under various water and N regimes, corn hybrids and soybean varieties were evaluated for grain P concentration and P removal. Four years of corn production without P addition lowered surface soil (0–15 cm) extractable P level (Bray and Kurtz no. 1) from 265 mg kg−1 to 171 mg kg−1 in the biennial N‐based compost treatment. Based on a decay equation, it would have required 10 yr of corn P removal to lower the soil P level to the original 69 mg kg−1 that existed before treatment application. The rate of decrease in extractable soil P was greater when soil P was higher and reduced with decreasing soil P level. Most of the P in the plants was absorbed from the 0‐ to 15‐cm soil depth since no significant reduction in soil P level was observed from 1996 to 1999 in the 15‐ to 30‐cm soil depth. Across 2 yr, there was as much as 54% difference among corn hybrids for grain P removal. The differences in P concentrations among corn hybrids indicated that hybrids could be selected for low P uptake when lower P level in ethanol production by‐product or in animal ration and subsequently in manure is desired. Soybean grain P concentration was nearly twice that for corn but grain P removal was less for soybean than for corn. Crop P removal can significantly reduce soil P level with time.

Variation of early growth and nutrient content of no‐till corn and soybean in relation to soil phosphorus and potassium supplies1

Knowledge of relationships between variation in early plant growth and soil nutrient supply is needed for effective site‐specific management of no‐till fields. This study assessed relationships between soil test phosphorus (STP) and potassium (STK) with early plant growth and P or K content of young corn (Zea mays L.) and soybean [Glycine max (L.) Merr.] plants in eight no‐till fields. Composite soil (0–15 cm depth) and plant (V5‐V6 growth stages) samples were collected from 400‐m2 areas at the center of 0.14‐ha cells of a 16‐cell square grid and from 2‐m2 areas spaced 3 m along each of two 150‐m intersecting transects. Correlation, regression, multivariate factor analyses were used to study the relationships between the variables. Variability was higher for samples collected from the transects. Plant dry weight (DW), P uptake (PU), and K uptake (KU) usually were correlated with STP and STK but the correlations varied markedly among fields. Relationships between soil and plant variables could not always be explained by known nutrient sufficiency levels for grain production. Plant P concentration (PC) was not always correlated with STP and sometimes it increased linearly with STP, but other times increased curvilinearly until a maximum was reached. Plant K concentration (KC) usually was correlated with STK, however, and increased linearly with increasing STK even in fields with above‐optimum STK. The results suggest greater susceptibility of early growth to STP than to STK and greater plant capacity to accumulate K compared with P over a wide range of soil nutrient supplies. Variation in STK likely is a major direct cause of variation in KC over a wide range of conditions but variation in STP is not likely a major direct cause of variation in PC when high STP predominates.