Use of Biosolids Incinerator Ash as a Phosphorus Source for Turfgrass

This experiment was conducted to investigate the use of biosolids incinerator ash from the Allegheny County Sanitary Authority (ALCOSAN) as a phosphorus (P) source for turfgrass soils.


Biosolids incinerator ash is a dry, powdery, mineral material that consists mostly of silt sized grains. Organic material, organic chemicals, and all microbes in the original biosolids are incinerated. Inorganic constituents of the original biosolids are concentrated in the ash. The ash contains 4-5% total P and therefore has potential value as a source of P for plant nutrition.

We conducted a field experiment to determine if biosolids incinerator ash is an effective source of P for turfgrass, and to determine if the ash could be beneficially used as a component of manufactured topsoil for landscaping. Major environmental concerns with this use of biosolids incinerator ash include determining appropriate ash addition rates to avoid excessive P loading and potential P runoff or leaching, and loading and availability of trace elements.

In preliminary laboratory work we combined incinerator ash or triple super phosphate (TSP) fertilizer with a low P-test soil on the basis of the total amount of P added. Rates of P addition ranged from 0 to 140 mg P/kg soil. We incubated the mixtures at room temperature and allowed them to run through several wetting and drying cycles. Bray P1 extractable P was determined on the mixtures. Results of the incubation are shown below.

Ash and TSP

These data indicate that TSP fertilizer is approximately four times more effective than the biosolids ash at increasing the Bray P1 soil test. This indicates the P in the ash is far less soluble than the P in TSP.

Based on these results we established a field experiment to investigate turfgrass response to blending ash with soil on a P basis. Using a low P topsoil material we combined ash with soil at rates of 0, 0.9, 1.8, and 3.6 % on a dry weight basis. Based on the incubation study, these rates of addition should be equivalent to 0, 0.5, 1.0, and 2.0 times the amount of P needed to increase soil test P to recommended levels for turf.

Trace element concentrations in the ash are given below. At the 1.8% rate of ash addition to soil, calculated total trace element addition to the soil is shown below and compared to the regulatory cumulative pollutant loading limit (CPLR) for biosolids application.

Trace element concentration in ash.
Trace element Concentration in ash
Addition with 1.8% ash

Field Experiment Setup

The field experiment consisted of 5 treatments. The topsoil with no amendment (control), topsoil with recommended TSP fertilizer, and ash mixed with topsoil at rates equivalent to 0.5, 1.0, and 2.0 times the amount of P added with TSP fertilizer. Screened soil and ash were blended at these rates on a weight basis. Soil/ash blends where placed in 10' x10' plots which were approximately 10" deep and were arranged in 3 randomized complete blocks. Plots were staked and separated by silt fence. Volume of soil needed to fill one plot was placed in a soil shredder along with the needed weight of ash to achieve the desired mix ratio. Soil and ash were thoroughly mixed in the shredder, fed into a dump truck, and dumped in the appropriate field plot. Mixed soil was evenly spread over the plot using hand shovels and rakes. The TSP fertilizer (3.3 lb/plot) and muriate of potash (KCl) fertilizer (0.5 lb/plot) was spread on the surface of TSP treatment plots and mixed into the soil using hand shovels and rakes. All plots received surface application of urea (0.5 lb/plot) and ground agricultural limestone (6.3 lb/plot). These materials were incorporated by hand using shovels and rakes. The entire plot area was broadcast seeded with 5.5 lb of perennial ryegrass seed (Lolium perenne, L.) followed by a light raking and mulched with clean wheat straw. The plots were watered as needed to maintain growth of ryegrass.

Following a six week establishment period, the ryegrass was mowed approximately once per week until fall growth ended. Plots were again mowed once each week when growth resumed in the spring of 2003. On alternate mowing dates the ryegrass growth on each plot was sampled for yield determination and tissue analysis. Sampling dates in Fall 2002 were 9/24, 10/10, 10/24 and 11/8; and in Spring 2003 were 5/2, 5/16, 5/30, 6/13, and 7/2. Sampling was done using a modified rear discharge bagging mower that blew grass clippings into mesh filter bags. Plot boundaries were first mowed and samples for yield measurement and tissue analysis were collected by mowing a single pass across each plot. Length and width of the sampled area was measured. Clippings were dried for 48 hours at 65ÂșC and weighed. Two 10 g composite samples for each plot, representing fall 2002 and spring 2003 samples, were made by mixing tissue material from each harvest in ratios based on contribution of each cutting to total yield. Composite tissue samples were analyzed at the Penn State University Ag Analytical Services Lab for N, P, K, Ca, Mg, Al, Mn, Fe, B, Cd, Co, Cu, Mo, Na, Ni, Pb, and Zn. Spring 2003 composite samples were also analyzed for As, Se, and Hg.

During the fall of 2002 and spring/summer of 2003, grass growth, grass nutrients and trace element content were measured. We conducted soil tests to determine soil test P response and total trace element concentrations.

Results and Discussion

Soil Phosphorus (p)

ALCOSAN biosolids incinerator ash was effective at increasing Mehlich3 P levels (Figure 2). Increasing amounts of ash resulted in linear increases in soil P and there was very little decay in soil P levels during the experiment. By contrast, soil test P levels were initially much higher with trisodium phosphate (TSP) fertilizer than with ash and then decreased substantially within 3 months. This result reflects the much more soluble nature of P in TSP than in ash. The first soil samples were collected immediately after treatment application, before there was any opportunity for TSP fertilizer granules to dissolve and react with the soil. During the next 3 months soil test P decreased substantially in the TSP treatment, presumably a result of soluble P reaction with, and strong sorption on, soil constituents. Mehlich3 P levels with TSP and the 1x ash application rate remained similar throughout the experiment. The total amount of P applied in the 1 x ash rate was 4.1 times greater than the total amount of P applied in the TSP. This result substantiates the preliminary incubation study that indicated ash P was approximately 25% as effective as TSP at increasing soil test P levels. These results indicate that about 75% of the P in biosolids incinerator ash is highly insoluble and is unlikely to be available for plant uptake.

Mehlich3 Phosphorus

Figure 2. Effect of ash addition on Mehlich3 extractable phosphorus.

Rye Grass Yield

Fall establishment and growth of ryegrass was improved by ash addition. Visual observation of the plots indicated turf establishment, density, and color was poorer in control plots than in all other treatments (see picture below, control plot is in lower left corner).

Fall Establishment of Ryegrass

Such differences were no longer visible in Spring 2003 when growth on all plots was more vigorous and turf density was greater than in the previous fall (see picture below, control plot is in lower left corner).

Spring 2003 Growth

Dry matter production by ryegrass increased with increasing ash addition in Fall 2002 (see graph below). Ash was equally effective as TSP fertilizer at stimulating turf establishment and early growth of ryegrass. Increased ryegrass growth with ash application was apparently due to increased P availability.

Ryegrass Yield

Tissue Phosphorus Concentrations

Tissue phosphorus concentrations were increased by ash in the fall of 2002 with much smaller increases in spring 2003 (see graph below). Lower overall P concentrations in spring 2003 tissue reflects the diluting effect of greater dry matter production and possibly reduced availability of soil P in the spring of 2003. Again, ash was equally effective as TSP in providing P for turf growth.

Tissue Phosphorus

Work was completed in the Summer of 2003.