Rate and Placement Effects of Phosporus and Potassium Fertilizer on Irrigated Pea

Introduction

Pea is an important crop under irrigation, from both an economic and rotational perspective. Optimal production requires suitable cultural practices including proper fertility management. Early seeding increases yield and improves quality. Cool soil temperatures associated with early seeding can reduce the availability of phosphorus and potassium. A study was conducted in the Outlook irrigation district in 1992 and 1993 to examine the effects of phosphorus and potassium fertilization on irrigated pea production.

Methodology

The test was conducted on a bradwell very fine sandy loam soil. Radley peas was seeded at 20 cm row spacing and a density of approximately 60 plants/m². Soil tests indicated sufficient potassium and recommended 30 to 40 kg P₂O₅/ha in 1992 and 25 to 35 kg P₂O₅/ha in 1993. The fertilizer was either side-banded or seed-placed.

The fertilizer treatments consisted of 0, 17, and 34 kg K20/ha in the form of potassium chloride (0-0-60) and 0, 22, 44, 66 and 88 kgp2o5/ha in the form of monoammonium phosphate (11-51-0).

Irrigation and other cultural practice were performed according to standard recommendations. The total precipitation and irrigation in 1992 and 1993 was 278 mm and 400 nim, respectively. The peas were direct harvested, cleaned and yields adjusted to 16% moisture.

Results

Plant Stand

Potassium application had no effect on plant stand. In both years increasing phosphorus rates tended to reduce plant stand and the effects were significant in 1993 where the fertilizer was seedplaced compared to side-banded (Table 1). For example, there was a 17% reduction in plant stand when seed-placing 66 and 88 kg P₂O₅,/ha compared to 0 or 22 kg P₂O₅/ha application.

LSD at P < 0.05 for Placement X P interaction = 6.0
*Average potassium rate.

Yield

In 1992, analysis of variance showed significant phosphorus rate main effect and potassium rate X placement interaction and in 1993, the various treatments showed no significant effects on seed yield. Phosphorus application produced significantly higher yields than the check treatment. Application of 44 kg/ha of P₂O₅ produced the highest seed yield which was 12% higher than 0 phosphorus (Table 2). Phosphorus rates higher than 44 kg/ha P20, tended to reduce yield. There was no distinct phosphorus placement effect.

LSD for phosphorus main effect at P < 0. 05=303 kg/ha.
* Average of placement and potassium rates.

Yield response to increased potassium application were different for the two placement treatments. Seed yield decreased with increasing rate of seed-placed potassium and responses were significant in 1992 (Table 3). On an average, seedplacement of potassium reduced seed yield by 3.0% in 1992 and 1.0% in 1993 compared to side-banding.

LSD at P <0.05 for Placement X K interaction=307 kg/ ha.
*Average of phosphorus rates.

Seed Weight

Potassium fertilization has been suggested to improve seed quality through increase weight. No significant increase in seed weight to any fertilizer treatments were observed in this study.

Summary

Irrigated pea responded differently to phosphorus and potassium fertilization in both years in this study. Side banding of fertilizer produced yields than seed placed fertilizer. Generally, high rates of seed placed fertilizer that high salt index can reduce seedling emergence resulting in lower stands. Increased rates placed potassium and phosphorus resulted in lower plant stands which may result reduction in seed yields. However in reduction in plant stand did not affect seed yield. The 1993 growing season was cool and moist resulting in high disease levels which may have masked the effects of the fertilizer treatments. Seed weight was not affected by phosphorus, potassium fertilizer rates or placement.

Recommendations

* Side band potassium and phosphorus fertilizer instead of placing it with the seed