Phosphorus Availability for Corn and RyeGrass
in Organic-Based Fertilizer-Amended Soils

Hountin, J.A. and J.W. Paul
Agriculture and Agri-Food Canada
Pacific Agriculture Research Centre

Animal manures contain significant concentrations of nitrogen (N) and phosphorus (P), and their utilization for crop production is beneficial in terms of nutrient recycling and reducing commercial fertilizer use. With intensive animal production, it is difficult to recycle manure nutrients for crops. Composting and production of value-added organic based fertilizers is one approach to improve nutrient recycling because the nutrients are concentrated and therefore more economical to transport than raw manure.

One technique of organo-mineral fertilizer (OMF) production used in Europe consists of mechanically mixing commercial fertilizer with peat, followed by pelleting and drying (Richards et al. 1993). The advantages to using OMF include the "slow release" effect, where the rate of nutrient release can be controlled by the diameter of the pellet. In North America, OMF is also being produced from composted poultry manure mixed with fine or granular ammonium nitrate fertilizer. We also produced organic-based fertilizer (OBF) using various compost materials mixed with inorganic fertilizer.

In addition to characterize the release rates of N from these fertilizers, it is also important to understand the fate of phosphorus. This is important for optimal phosphorus uptake by plants as well as minimizing environmental pollution through phosphorus runoff. The organic ligands present in OMF or in manure compete with phosphorus at the same adsorption sites in soil. This increases the release rate of phosphorus adsorbed onto the soil (Singh and Jones, 1976).

The objectives of this research were to: (i) determine if phosphorus availability from OBF for corn and if soluble phosphate leaching in the high rainfall conditions of south coastal British Columbia (B.C.) were affected by a mixture of commercial granular fertilizer and compost materials, and (ii) compare the P efficiency from three new OBF products to that of inorganic fertilizer and a commercially available organic-based fertilizer.

Three new different sources of organic materials were composted and used in this study as follows: LHPM - a mixture of hog liquid manure (50%) and poultry broiler litter (50%) was composted for two months using enhanced moisture removal; DPM—a mixture of separated dairy solids and poultry broiler litter, and BSC—biosolids (75%) and poultry broiler litter (25%) composted for six weeks using enhanced moisture removal. Chemical fertilizers were added to the composts to make three new organic based fertilizers (OBF). The LHPM and DPM fertilizers were pelleted and crumbled to give approximately 2-3 mm size products. The fertilizers were analyzed in laboratory and their chemical composition was comparable to a commercial organic-based fertilizer available in B.C. (Table 1).

A field experiment was carried out our research centre on a fine silt loam soil cropped to silage corn (Zea mays L.) Treatments included four rates of chemical fertilizer N (0, 75, 150 and 225 kg N ha^-1) and two rates of OBF-N (150, 225 kg N ha^-1) surface applied immediately prior to planting. Soil cores at depth increments of 0-15, 15-30 and 30-60 cm depth were taken before fertilizer application, at the sixth leaf stage of corn growth, and after corn harvest in October. The soils were extracted for Bray-P1and soluble phosphorus determination (Sharpley, et al.1996).

A greenhouse experiment was conducted on two soil types, a clay loam and a sandy loam. Pots contained 3 kg of soil which consisted of a 75% soil and 25% silica sand mixture. Ryegrass (Lolium perenne L.) was planted in each of the pots, and two cuts (40-60 cm height) were harvested before addition of fertilizers in order to establish the grass and deplete some of the soil nutrients. Treatments consisted of four OBF fertilizers at each of two rates (150 and 300 kg N ha^-1 equivalent) in each soil. A N and P free nutrient solution was provided to provide other nutrients. Four cuts of grass were harvested during a 16-week period. The soil was analyzed for Bray-P1 and water soluble P at the beginning of the experiment, and after completion.

In the field experiment, silage corn yields and total P uptake from OBF and inorganic fertilizer treatments were significantly higher than the control, but not significantly different from each other (Table 2). There was no effect of increasing rates of P. This was probably due to the high soil test-P. Paul and Beauchamp (1993) reported similar results during the first year in a 3-year field trial from a silt loam cropped to maize. OBF-amended treatments contained a significantly higher P concentration than inorganic fertilizer treatments and the control. Phosphorus uptake was significantly correlated with water soluble P_w (r=0.51) and with corn yield (r=0.81). Our results were similar to that of Guang et al. (1997). The intensity factor (Qi) represents the quantity of P in soil solution available for plant growth. The Qi that is critical for growth of most plants ranges between 0.01 to 0.2 ppm (Fox and Kamprath, 1970). In this experiment, the Qi ranged from 0.05 to 2.08 ppm and was dependant on the organic and chemical fertilizer sources and application rates of OBF based either on N or manure-P.

In the greenhouse experiment, both soil type and OBF treatment significantly affected cumulative dry matter yields (Figure 2). Yield response was greater on the clay loam than on the sandy loam. This is probably due to more available P in the sandy loam than in the clay loam, even though total P was higher in the clay loam than in the sandy loam. The highest yields were obtained with LHPM fertilizer in clay loam and with DPM fertilizer in the sandy loam. The new organic based fertilizer products performed at least as well as the commercially available product. Additional results on P uptake by the ryegrass will be presented later when analyses are complete.

Phosphorus from the new organic fertilizer materials was readily available for a corn crop in a one-year field experiment. Ryegrass yields in the greenhouse experiment showed that nutrients in the new organic fertilizer products were readily available as demonstrated by the superior growth. Crop response was significantly affected by soil type. Further research is required to determine whether manure application should be based on phosphorus or nitrogen.

Figure 2. Ryegrass yield in a greenhouse experiment using various inorganic and organic-based fertilizers on a sandy loam and a clay loam.

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