Effect of time and moisture on the efficacy of an encapsulated nitrification inhibitor

Andrew D Ferrel, Purdue University

Abstract

Instinct is a polymer encapsulated formulation of nitrapyrin that is marketed to be mobile within soil and is to be co-applied with N fertilizers such as urea, urea ammonium nitrate, starter fertilizers, or manure. Instinct is ineffective as a nitrification inhibitor until nitrapyrin is released from its microcapsule, after which nitrapyrin will then begin to inhibit nitrification. According to the product label, if no rainfall occurs within 7-10 days following the surface application of N fertilizer amended with Instinct, it is recommended that the N fertilizer and Instinct be incorporated into the soil. This leads one to believe that nitrapyrin is expected to be released from its microcapsule shortly after 7-10 days. A series of laboratory experiments was conducted under controlled conditions to study the effect of Instinct on the nitrification process. The main objectives of this series of experiments were to determine: 1) the time when Instinct becomes an effective nitrification inhibitor after co-application with N fertilizer, 2) the effect of soil type on the effectiveness of Instinct, and 3) the effect of soil moisture on the effectiveness of Instinct. The effect of time and soil type on the effectiveness of Instinct was examined in two experiments conducted at high and low N application rates [868 and 44 mg N kg-1 added as (NH4)2SO 4] in three soil series. Instinct was applied at the recommended rate of 2.6 L ha-1 and was pre-incubated for 7, 14, 21, 28, 35, and 42 days, followed by an application of N fertilizer. Samples were then returned to the incubator for a three week post-incubation period to allow nitrification of the N fertilizer to occur. All samples were incubated at 25°C and maintained at 0.03 MPa moisture content for the duration of the experiment. A second experiment was conducted to compare the effects of dicyandiamide (DCD), another commercially available nitrification inhibitor, and Instinct on nitrification in an Avonburg silt loam soil. Instinct and DCD were applied at their respective recommended rates and (NH4)2SO 4 was applied simultaneously at a rate of 87 mg N kg-1, as well as at delayed time periods of 7, 14, 42, and 49 days after inhibitor application. A three week and two week post-incubation period of N application in the first and second runs of this experiment, respectively, allowed nitrification of the N fertilizer to occur. All samples were incubated at 25°C and maintained at 0.03 MPa moisture content for the duration of the experiment. A final set of experiments examined the effect of moisture on the effectiveness of Instinct. Instinct was applied to a Tracy sandy loam soil series at the recommended rate of 2.6 L ha-1 and maintained at 0.18 g g -1 (0.03 MPa), 0.14 g g-1, 0.10 g g-1, or 0.04 g g-1 gravimetric water content for a pre-incubation period of 10 days. Application of (NH4)2SO4 was at a rate of 87 mg N kg -1, 10 days following Instinct application, and all samples were then brought to 0.18 g g-1 gravimetric water content and incubated to allow nitrification to occur. All samples were incubated at 21°C. After each experiment, soil was analyzed for NH4-N and NO3-N following incubation to determine effects of the treatments on Instinct effectiveness. Time, moisture, and soil type had no effect on the effectiveness of Instinct within the incubation period tested. Instinct did not affect the nitrification process in any experiments. When DCD was used as a comparison in one experiment, DCD increased soil NH4-N 3-fold when added with N fertilizer when compared to added N with and without Instinct.

Degree

M.S.

Advisors

Camberato, Purdue University.

Subject Area

Agronomy

COinS