Field testing of Lorganic-8 (hereafter referred to as LO-8) indicated the liquid hydrolysate has slow-release N properties and more N is microbially mineralized than from other natural organic turf fertilizers. The purpose of this laboratory study was to verify these field observations.

METHODS

The laboratory incubations were carried out with incubation filters containing 50 g of an 80/20 (v/v) mix of sand and sphagnum peat to which 1 % silt loam soil was added to ensure good microbial populations. The medium was adjusted to its moisture holding capacity of 14.7% (wt) at a 25-cm tension. Samples of each of the natural organic turf fertilizers listed in Table £ were weighed and spread on the sand-peat surface. The weight of each material was that which contained 30 mg of organic N. The filter funnels were then enclosed in 0.05-mil plastic bags to prevent drying but allow for gas exchange with the atmosphere. The mineralization units were then incubated at 68 or 90⁰F.

After incubation periods of 7, 14, 28 or 42 days, inorganic N was leached from each incubation filter with 50 ml of 0.005 M CaCi₂. Twenty-five centimeters tension was applied during leaching to return the soil-peat mixes to their original moisture contents. Inorganic N (NH₄+ and N0₃=) was then determined in the extracts by way of the Kjeldahl procedure.

RESULTS

General properties of the fertilizers used in this study are presented in Table 1. Milorganite, Hou-Actinte, and Flororganic are sewage sludge products from Milwaukee, Houston, and Tampa, respectively. Sustane is composted turkey manure + pine bark bedding. The composted poultry manure is from a Wisconsin egg production facility. The sample of LO-8 used was 0.15% N below grade, a problem that has since been rectified in the manufacturing process. The data confirm that for all practical purposes the N in LO-8 is 100% organic.

When incubated at 90⁰F, the near ideal temperature for microbial activity, slightly more N was released from Sustane than from LO-8 and Milorganite (Figure 1) Nitrogen mineralization from Hou-Actinite and the poultry compost was somewhat less. The least amount of N released was that from Flororganic.

Nitrogen mineralization at 68⁰F rather than 90⁰F was markedly different. At this suboptimal temperature, LO-8 stood out in terms of the amount of N released (Figure 2). Sustane was next, but the percentage of organic N released was 12% lower than from LO-8. Only 14 to 15% of the organic N in the poultry compost and Flororganic was mineralized. From this, it is clear that N mineralization from LO-8 is far less temperature dependent than from the other products tested.

Figure 3 shows the sharp contrast between LO-8 and Milorganite in the effect of temperature on organic N mineralization. The effect of temperature on LO-8 organic N mineralization

was almost imperceptible. This figure also shows that after 7 days the mineralization of N from LO-& is considerably more uniform over time than from Milorganite.

By taking into account the total N contents of the fertilizers tested and the amounts of N mineralized from them in 42 days, one can calculate the quantities of each that are theoretically required to provide turfgrass with the same amount of N as might be provided by 1.0 lb LO-8/

M. As shown in Table 2, at 68⁰F, these weights range from 2.1 lb/M for Hou-actinite to 5.2 lb/M for Flororganic. These weights are understandably less at 90⁰F, but still range from 1.3 to 2.1 LB /M.

CONCLUSIONS

The results of this laboratory incubation study support the following conclusions:

1. The mineralization of the organic N in LO-8 at 68⁰F is substantially greater than from the sewage sludge or poultry compost turf fertilizers tested;

2. At 90⁰F, organic N mineralization from LO-8, Sustane, Milorganite, Hou-Actinite and poultry compost is so similar that differences would likely be undetectable under field conditions;

3. The N mineralization pattern for LO-8 is more uniform over time than for the other products tested;

4. Due to differences in N content and N mineralization rates, turf managers can expect to have to apply fewer pounds of LO-8 than the other fertilizers tested to achieve the same level of turfgrass color.

The results of this incubation study confirm the field observation that LO-8 possesses slow-release N properties and explain why excellent Kentucky bluegrass color was achieved with as little as 1.6 lb. N/M over an 18-week season.

| Lorganic-8 Home | Reports |