K. 2015. Nutrient status and crop productivity following a 14-year irrigated potato rotation study. Can. J. Plant Sci. 95: 351Á360. Well-managed crop rotations contribute to high productivity and quality in subsequent crops, and neither excessively deplete nor increase soil nutrient levels. A field experiment was conducted in the year following completion of a 14-yr irrigated potato (Solanum tuberosum L.) rotation study to assess the impact of preceding rotation on soil P, K and micronutrient concentrations, and on soybean (Glycine max) productivity, yield and seed nutrient levels. Soybean was grown on six established rotations [potato with canola (PC), wheat (PW), canolaÁwheat (PCW), oat-wheat (POW), wheatÁcanolaÁwheat (PWCW), and canola underseeded to alfalfaÁalfalfaÁalfalfa (PCAA)] arranged in a randomized complete block design (RCBD) with four replicates. Soil nutrient levels fell within ranges typical of the region, as did soybean yield and quality. Lower P and K concentrations in spring soil samples, and in soybean seeds, were typically associated with PCAA, suggesting that fertilizer additions did not account for high rates of P and K removal by alfalfa hay in this rotation. While preceding rotation had minimal effects on soil Cu and Zn, soybean established after PCAA or after potato contained comparatively higher seed Cu and Zn concentrations suggesting that including mycorrhizal crops such as potato and alfalfa in rotation may have contributed to enhanced micronutrient availability. Soybean yield was 4Á6% higher following potato than canola or cereals, and 6% higher following POW than PCW. Seed protein increased and oil concentration decreased where preceding rotations included alfalfa. The limited yield differences observed may have been due, in part, to the selection of soybean as an indicator crop, which likely minimized differences among rotations arising from disease, weeds and nitrogen. These findings suggest that, with careful management of irrigated potato systems over the longer term, crop productivity and nutrient availability may be maintained within acceptable levels for agricultural production. Bien ge´re´s, les assolements concourent a`une productivite´et aù ne qualite´e´leve´es des cultures subse´quentes; ils n'appauvrissent et n'enrichissent pas davantage excessivement le sol. Les auteurs ont proce´de´a`une expe´rience sur le terrain l'anne´e suivant l'ache`vement d'une e´tude de 14 ans sur un assolement de pomme de terre (Solanum tuberosum L.) avec irrigation. L'objectif consistait a`e´valuer l'impact de l'assolement ante´rieur sur la concentration de P, de K et d'oligoe´le´ments dans le sol ainsi que sur la productivite´du soja (Glycine max), son rendement et la concentration de nutriments dans la graine. Le soja a e´te´cultive´sur six assolements [pomme de terre avec canola (PC), ble´(PB), canola-ble´(PCB), avoine-ble´(PAB), ble´-canola-ble´(PBCB) et canola avec semis sous couverture de luzerne-luzerne-luzerne (PCLL)] dans un dispositif en blocs ale´atoires complets avec quatre re´pe...

Khakbazan, M., Henry, R., Haung, J., Mohr, R., Peters, R., Fillmore, S., Rodd, V. and Mills, A. 2015. Economics of organically managed and conventional potato production systems in Atlantic Canada. Can. J. Plant Sci. 95: 161–174. A rotation study was initiated in 2007 in Prince Edward Island (PEI), Canada, to determine the economic effects of converting from conventional potato production to organically managed systems. Seven organically managed rotations, which used various crop combinations to help control pests and soil-borne diseases as well as maintain nutrient levels, were assessed for 2 yr before and 2 yr after organic certification requirements were met in 2009. Each rotation included potato as the main cash crop and at least one other cash crop in a 4-yr rotation and these rotations were compared to a 4-yr conventional rotation. Results indicated that without an organic price premium, significant net revenue losses are expected for most of the seven rotations because of lower yields and high costs. The rotation that included carrots (potato, carrots and mixed peas–oats grain as the cash crops) produced the highest net revenue amongst all rotations studied; however, carrot yield and the net revenue associated with it also showed the greatest variability among all the crops. Organically managed cash crops generated higher net revenues than the conventional potato system only if the average PEI organic price premium was applied. Conventional potato systems produced economic benefits similar to most of the organic rotations when a traditional potato–cereal–green manure rotation was evaluated. The comparison of seven possible rotations provides producers with options if growing organic potatoes.