Her Majesty the Queen in Right of Canada as represented by the Minister of Agriculture and Agri-Food Canada. No part of this periodical may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. aBstractStrategies to improve sustainability are important in intensively managed potato (Solanum tuberosum L.) systems. Th is study has assessed rotation systems and N sources to mitigate potato yield and soil organic matter decline in Prince Edward Island (PEI), Canada. Th ree-year potato rotation systems were initiated in 2006: continuous potato (CP); potato-barley (Hordeum vulgare L.) underseeded with red clover (Trifolium pratense L.)-red clover (PBR); and potato-barley-sorghum sudan grass ([Sorghum bicolor L.) used as green manure])/winter rape (Brassica napus subsp. rapifera) (PBSW); and potato-barley-canola ([Brassica napus susbsp. napus] used as green manure)/winter rape (PBCW). Th ree diff erent N sources (mineral N fertilizer, liquid hog manure, and lobster fl ake) were applied in a split-plot fashion during the potato phase. Potatoes were grown in 2006, 2009, 2012, and again in 2013 to evaluate residual eff ects. In 2012, total N or total C in the whole soil, in particulate organic matter or in the slurry fractions were not aff ected by N sources or rotation systems. Th e PBSW and PBCW rotations generated signifi cantly higher potato yields in 2009 and 2013, whereas the CP rotation produced signifi cantly lower potato yields in 2 of 4 yr. Th e addition of lobster fl ake suppressed yield compared with other N sources in 3 of 4 yr. Th e PBR rotation, which is common in PEI can increase nitrate losses over winter. Alternatively, the PBSW and PBCW rotations may represent a good substitute to the PBR rotation as they can increase potato yield while minimizing nitrate losses.Agriculture and Agri-Food Canada, Crops and Livestock Research Centre,

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Potato production is critical to economy of Prince Edward Island (PEI), but has been linked to increasing groundwater nitrate contamination and anoxic events in estuaries. Given that PEI is entirely groundwater-dependent for potable water, this has resulted in considerable pressure to find solutions to protect water quality. However, our understanding of the controls on nitrate loading to groundwater, and the consequent potential to mitigate nitrate loading through beneficial management practices (BMPs), is limited. In PEI, flow and nitrate transport in the vadose zone are controlled by the matrix porosity of the till and sandstone, while flow and transport in the saturated zone are controlled by a conductive fracture network with limited storage capacity. Diffusion of nitrate stored in the matrix may introduce a significant time lag between reduced nitrate loading from implementation of BMPs and measureable improvement in groundwater quality. BMPs with potential to mitigate nitrate loading to groundwater through improved nitrogen fertilizer practices in producing potato crops have been identified, but implementa

High levels of nitrate leaching losses from potato rotation systems have caused concerns for both drinking water quality and aquatic ecosystem protection in Prince Edward Island (PEI). Paired-field experiments were carried out in commercial fields to evaluate the potential of delayed plowing forages within potato rotation from fall to spring on reducing nitrate leaching at two separate sites in PEI during 2010 and 2013. Monitoring showed that fall plowing resulted in elevated tile-drain nitrate concentrations compared to spring plowing, probably mainly due to crop residue mineralization during fall which was hastened by earlier herbicidal termination of forage (i.e., herbicidal killing) at Site 1. A similar trend was also observed regarding nitrate concentrations of shallow groundwater at Site 2 during the forage phase. The practice of delaying the plowing of forages and/or associated earlier herbicidal termination of forage until spring reduces forage-phase nitrate leaching loss by 20 to 61%, and should therefore be encouraged for nitrate mitigation. The study also demonstrated that only a small fraction (9.6 to 22%) of the fall plow-down forages decayed during the forage phase and a large portion was retained in the soil into the next season. Growers should consider accounting for some of the carried-over N for the subsequent crops regardless implementing fall or spring plowing.

A growth chamber study was conducted to evaluate the effect of application of phosphate fertilizer on soil solution dynamics of cadmium (Cd) and Cd accumulation in durum wheat (Triticum turgidum L. var. durum). Treatments consisted of three phosphate fertilizer sources containing 3.4, 75.2, and 232 mg Cd kg −1 applied at three rates (20, 40 and 80 mg P kg −1 ) plus a no fertilization control. An unplanted treatment at 40 mg P kg −1 was included to separate the effects on soil solution Cd dynamics of the crop from that of the fertilizer. Soil solution samples were obtained using soil moisture samplers every 10 days after germination. The experimental results indicated that plant biomass significantly increased with P application rates and decreased with increased Cd concentration in the phosphate fertilizers. Total cadmium concentration in soil solution was not consistently affected by phosphate fertilization rate and fertilizer sources, and therefore Cd concentration in the fertilizer. Application of phosphate fertilizer, however, increased the concentration and accumulation of Cd and shoot Cd/Zn ratio, and decreased shoot Zn concentration in durum wheat. Phosphate sources had a marginally significant effect (P=0.05) on shoot Cd concentration and did not affect Cd accumulation in durum wheat. Concentration of Cd in soil solution was unrelated to Cd concentration in durum wheat. These results suggest that the immediate increase in Cd concentration and Cd accumulation in durum wheat with phosphate application is due more to competition between Zn and Cd for absorption into plants, enhanced root to shoot translocation and enhanced root development, than to a direct addition effect from Cd contained in phosphate fertilizer. In the short term, application of phosphate fertilizers can increase Cd concentration in the crops, regardless of the Cd concentration of the fertilizer. An optimal P fertilization, possibly in combination with Zn application, may offer an important strategy for decreasing Cd concentration and accumulation in crops.