Strategies to build sustainable P levels and optimize water use efficiencies on low P soil
Term: 4 years, beginning in 2023
Status: Ongoing
Researcher(s): Gursahib Singh, Irrigation Crop Diversification Corporation
SaskCanola Investment: $152,231
Total Project Cost: $509,010
Funding Partners: TBC
Objectives
Identify appropriate phosphorus (P) fertilization strategies on an irrigated field with low soil available P.
Investigate if P fertilizer additions influence plant Zn uptake.
Evaluate water productivity performance over a range of P fertilization strategies and provide produce with water productivity.
Project Description
Saskatchewan soils are among the lowest in North America with respect to available P levels. Reasons for this observation includes uncontrollable factors such as soil parent material, however, present agricultural practices have also contributed to low soil P values. These factors can include cultural practices, such as unwillingness to invest fertilizer dollars on rented land and risk aversion (short or long term) in terms of input investment, markets, or yield limiting growing season precipitation.
Implementing appropriate P fertilization strategies can potentially increase yields and reduce input costs and improve profitability. By providing knowledge and recommendations related to P fertilizer rate and application method, producers can make informed long-term P management decisions. Combined with water productivity data, current and future irrigated producers can improve water use efficiency and adopt environmentally and economically sustainable practices. This project offers a unique opportunity to investigate the importance of P fertilization to Saskatchewan producers and provide recommendations on the placement and amount of P fertilizer required to build soil P levels for long-term sustainability.
More than 80% of Saskatchewan soils are low in available phosphorus (P) and about 85% of annual cropland does receive P fertilization. In western Canadian soils, critical soil test available P levels have been reported from 15 to >30 ppm. Most Saskatchewan soils do not contain these critical levels, and many fall far below thresholds. Soils remain low because typical P fertilizer application rates are less than the amount of P exported in harvested grain. Typical annual application rates range from 10 – 30 kg P2O5/ha as the preferred placement is within the seed-row and higher rates can result in low germination or increased seedling mortality. These application rates are unlikely to exceed crop removal rates and therefore, soil P reserves decline. Broadcasting and incorporating large one-time applications of P fertilizer has been shown to build residual soil P levels. A six-year continuous cropping study in Saskatchewan compared 5 rates from 0 to 40 lb P2O5/ac of annual seed-placed P to 5 rates from 0 to 320 lb P2O5/ac of single broadcast and incorporated P. Over the first five years, the annual seed-placed P applications of 5, 10, 20 and 40 lb P2O5/ac increased grain yield by 10, 15, 24 and 29%, respectively. Broadcast P applications of 40, 80, 160 and 320 lb P2O5/ac increased average grain yield by 9, 24, 33 and 35% respectively. The 80 lb P2O5/ac increased yields to year 5 and had total yield and P uptake comparable to the annual seed-placed applications of 20 and 40 lb P2O5/ac. After the final 6th year of the study, the two highest broadcast applications, 160 and 320 lb P2O5/ac, had continuing grain yield responses and soil testing indicated yield responses would continue due to residual soil P levels. Smaller annual applications of P fertilizer benefit crop yield on most soils and may be enough to optimize grain yield for a single year. However, these applications will only build soil P if the difference between P applications and P removal is positive. A gradual build of soil extractable P has been observed in numerous trials in western Canada. On very low available P soils, small fertilizer P applications can have an agronomically important residual effect. The average wheat yield response to 20, 40 and 60 kg P2O5/ha was significantly increased at each incremental P rate addition. When re-cropped to canola without additional P fertilizer additions, residual P from previous applications continued to significantly elevate seed yield. Zinc (Zn) phosphorus interactions have been studied in a wide variety of crops and notably, high P applications can induce Zn deficiency. Zn deficiency is more prevalent in soils that are light textured, well drained (i.e. irrigated), low in organic matter, high in pH, calcareous, and low in available Zn. The proposed study location contains available Zn levels of 0.45 to 0.76 ppm (considered low to medium), therefore, it is important to monitor the influence of the proposed P fertilizer treatments on Zn uptake. Zinc sensitivity is crop specific dry bean, one of the highest valued and most widely grown annual pulse crop under irrigation, is sensitive to minor Zn deficiency while cereal crops like wheat and oats are less sensitive. Dry bean is included within the intended crop rotation, thus, will serve as the indicator crop within this study. Recent support by the provincial and federal governments to expand Saskatchewan’s irrigated acreage highlights the importance of irrigation and water resilience to the agricultural sector. Climate change preparedness and sustainable water management have been identified as factors that can provide the foundation for advancing the irrigation and water infrastructure projects. Although Saskatchewan agriculture is not currently limited by the availability of water, it is important to consider future needs (i.e., climate change, increased demand on water resources) and to implement practices that promote long term water sustainability. Water use efficiency, or water productivity, is linked to fertilization and is expected to vary based on P fertilizer rate and placement. Combined with fertilizer use efficiency results, water productivity can be used to identify efficient and effective irrigated production practices. This study hopes to balance long-term soil productivity with short-term crop P requirements while optimizing water productivity under irrigated production.