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This 2-yr (2013 and 2014) study evaluated the variation in tuber yield and selected indices of phosphorus (P) use efficiency of two new potato cultivars [AAC Alta Cloud (AC) and AAC Alta Strong (AS)] versus Russet Burbank (RB), the french fry industry standard. Initial P levels and P saturation index [(P/Al) × 100] ranged from 85 to 89.5 mg P kg −1 and from 4.6% to 5.6%, respectively. A complete randomized block design for each variety was laid out in three adjacent plots with six P fertilization rates. The average tuber yield ranged from 29.06 to 36.81 Mg ha −1 for AC, from 27.56 to 41.50 Mg ha −1 for AS, and from 38.15 to 42.02 Mg ha −1 for RB, with the highest yield observed in 2014. Tuber yield response to P application was described by the quadratic-plus-plateau model for AC and linear-plus-plateau model for AS with a mean critical (above which the yield response to P applications is unlikely) P rate of 40 kg P ha −1. Russet Burbank did not respond to P application. The trends of P uptake efficiency (PUE) for AC and AS mirrored that of tuber yield, while RB had a linear increase in PUE with P rate. The study highlights that current P recommendations for potatoes can be reduced without affecting yield, thus increasing farmers' economic returns. It also reveals the need to test optimal fertilization levels for new cultivars.

This study evaluated the effects of pre-plant treatments: deep ripping (DR), fumigation (F), deep ripping plus fumigation (DRF), deep ripping plus hog manure compost (DRC), and deep ripping plus fumigation plus hog manure compost (DRFC) in comparison with a non-treated control (NTC) on shoot and root performance of ‘Honeycrisp’ apple trees on M.4 rootstocks in an old orchard site with apple replant disease (ARD). Cylindrocarpon spp., Pythium spp., and Pratylenchus penetrans Cobb, all potential agents of ARD, were present in the orchard soil. Fine-root numbers (1 to 2.9 mm diameter) were significantly greater in the DRC and DRFC treatments than the DR treatment. After 6 years, trunk cross-sectional area (TCSA) and yield were largest for the DRFC treatment followed closely by F. The DR treatment had no effect on TCSA, yield, or yield efficiency when applied alone compared with the NTC. Contrast analysis demonstrated that F was significantly better than non-F for yield in all years and TCSA and yield efficiency in 2007. Also, there was a significant interaction between DR and F treatment in 2005 that significantly reduced yield in the DRF treatment. Contrast analysis showed that compost had a significant positive effect on yield in all three production years and TCSA and yield efficiency in 2007. Yield efficiency in the third production year was largest for F, DRC, and the DRFC treatments. Nutrient analysis revealed that soil phosphorus concentrations in compost-treated plots were double those in other treatments. High phosphorus content of compost may have contributed to the amelioration of ARD symptoms. This study found that in 2007, soil fumigation alone, as conventionally used for ARD control, and composted hog manure were equally effective in increasing yield and yield efficiency of apple trees planted in an ARD soil. The DRFC treatment was the overall best treatment in all years.

Core Ideas Data from 42 field trials were used to develop an agro‐environmental P model for potato based on soil P saturation index. A critical agronomic PSI (P/Al)M3 of 10% was identified, which corresponded to 85% of relative yield. Seven agro‐environmental P risk classes were identified with rates ranging from 21 to 105 kg P ha−1. Phosphorus is essential for potato (Solanum tuberosum L.), an economically important crop for the Canadian Maritime provinces. Nutrient loss, including P, into waterways and estuaries has contributed to reduced water quality such as algae blooms. The objective of this study was to develop an agro‐environmental model for potato based on the phosphorus saturation indicator (PSI) expressed as the ratio between Mehlich‐III extractable P and Al (P/Al)M3. A total of 42 field trials (6 conducted from 2000 to 2002 and 36 from 2013 to 2015) were conducted in Prince Edward Island (PEI), New Brunswick (NB), and Nova Scotia (NS) with six increasing P rates. A critical agronomic PSI of 10% was identified, which corresponded to 85% of relative yield. The P recommendation model was subdivided into seven P fertility and environmental risk classes with P rates ranging from 21 to 105 kg P ha−1, i.e., on average from one to five times the level of P removal by the potato crop, corresponding to the highest ([P/Al]M3 ≥ 14) and lowest ([P/Al]M3 ≤ 2.5) PSI levels, respectively. Only one site was in the very low fertility class. Additional trials are needed within this class to build a more robust and representative model. This is the first agro‐environmental P model for sustainable potato production that reduces the risk of P loss to watercourses in the region. The new P rates were developed at plot scale and need to be validated at larger scale.