Yield and Uptake of Phosphorus by Wheat and Canola Grown after Two Years of Forage Legume and Annual Crops

Rehemuti Miheguli,Paul G. Jefferson,Jeff J. Schoenau

doi:10.4236/ajps.2018.99132

Abstract

Annual legumes have been shown to enhance the growth and phosphorus (P) uptake by following rotational crops. However, there is lack of information on the effect of perennial forage legumes included in rotation for a short duration on yield and P uptake of crops like wheat (Triticum aestivum L.) and canola (Brassica napus L.) grown after the forage legume. A field study was conducted in four soil zones of Saskatchewan, Canada to assess: 1) the effect of two years of forage legume versus annual cereal, oilseed and grain legume on yield and P uptake of wheat and canola grown in the two subsequent years and 2) the effect of the complete four-year rotation on soil P dynamics and P balance. Four different crop sequences (alfalfa-alfalfa, red clover-red clover, barley-pea and barley-flax) employed over the first two years of crop rotation were compared as treatments followed by wheat and canola. Wheat grain yield was improved 32% - 60% by alfalfa (Medicago sativa L.) and red clover (Trifolium pretense L.) rotations at three of the four sites (P = 0.008, P = 0.001, P - 43% by red clover and alfalfa rotation at two sites (P = 0.013, P = 0.033). In the following year, positive yield benefits (55% - 64%) of having two years of alfalfa and red clover were observed at three sites. Four years of continuous cropping with a limited addition of fertilizer P resulted in a negative soil P balance and significant depletion of soil P fertility at all locations.

Highlights

A field study was conducted in four soil zones of Saskatchewan, Canada to assess: 1) the effect of two years of forage legume versus annual cereal, oilseed and grain legume on yield and P uptake of wheat and canola grown in the two subsequent years and 2) the effect of the complete four-year rotation on soil P dynamics and P balance
At Swift Current, yield depression occurred in wheat following two years of alfalfa rotation compared to the other crop rotations (P = 0.025), likely due to less precipitation at the Swift Current site over the course of the study compared to the other sites
The improved wheat and canola grain yields following two years of alfalfa and red clover are attributed to the well-known impacts on enhanced soil N supply and improved soil physical conditions, and likely reflect a positive effect on P availability in the short-term

Summary

Introduction

P deficiency is a major nutritional constraint for primary crop production in many N fertilized agricultural soils. Continuous annual application of P fertilizer is a common practice for correcting P deficiency and sustaining higher crop yield in many P-limited soils. Complete reliance on chemical fertilizers, in the long-run, is not considered to be an economically feasible and environmentally sustainable practice. Phosphorus fertilization increases the investments in crop production and enhances the risk of environmental pollution such as eutrophication and ground water contamination in some environments [5] [6]. The identification and incorporation of suitable crop species that are efficient in P mobilization is considered to be one of the promising agronomic approaches to access insoluble native soil P reserves and to capitalize on the use of accumulated residual soil P reserves [7] [8]

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