ALBERT

Description: Soil N supply is an important contributor of N to crop production; however, there is a lack of practical methods for routine estimation of soil N supply under field conditions. This study evaluated sampling just prior to topkill of whole potato plants that received no fertilizer N as a field bioassay of soil N supply. Three experiments were performed. In exp. 1, field trials were conducted to test if P and K fertilization, with no N fertilization, influenced plant biomass and N accumulation at topkill. In exp. 2, plant N accumulation at topkill in unfertilized plots was compared with mineral N accumulation in vegetation-free plots. In exp. 3, estimates of soil N supply were obtained from 56 sites from 1999 to 2003 using a survey approach where plant N accumulation at topkill, and soil mineral N content to 30-cm depth at planting and at tuber harvest were measured. Application of P and K fertilizer had no significant effect on plant N accumulation in two trials, and resulted in a small increase in plant N accumulation in a third trial. Zero fertilizer plots, which can be more readily established in commercial potato fields, can therefore be used instead of zero fertilizer N plots to estimate soil N supply. In exp. 2, estimates of soil N supply were generally comparable between plant N accumulation at topkill and maximum soil NO3-N accumulation in vegetation-free plots; therefore, the plant bioassay approach is a valid means of estimation of plant available soil N supply. Plant N accumulation at topkill in exp. 3 averaged 86 kg N ha-1, and ranged from 26 to 162 kg N ha-1. Plant N accumulation was higher for sites with a preceding forage crop compared with a preceding cereal or potato crop. Plant N accumulation was generally higher in years with warmer growing season temperatures. Soil NO3-N content at harvest in exp. 3 was less than 20 kg N ha-1, indicating that residual soil mineral N content was low at the time of plant N accumulation measurement. Soil NO3-N content at planting was generally small relative to plant N accumulation, indicating that soil N supply in this region is controlled primarily by growing season soil N mineralization. Use of a plant bioassay approach provides a practical means to quantify climate, soil and management effects on plant available soil N supply in potato production. Key words: Solanum tuberosum, nitrate, ammonium, N mineralization, plant N accumulation

Description: Field experiments were conducted at various locations in Prince Edward Island to determine the effect of applied Zn and B on tobacco (Nicotiana tabacum L.) yield, grade index, and tissue B and Zn concentrations. Addition of B at 1.1 kg ha−1 did not increase tobacco yield. Rates of B at 8.8 kg ha−1 and higher proved toxic and resulted in yield reductions. At these higher rates there was more than 3 μg g−1 hot-water-soluble (HWS) B in the soil and 113–169 μg B g−1 in the various primings. Tissue B levels as low as 31 μg g−1 in the third priming and the HWS B as low as 0.3 μg g−1 soil did not give B deficiency symptoms. Additions of Zn tended to increase yields but not significantly. Tissue Zn levels as low as 17 μg g−1 in the 3rd priming did not result in Zn deficiency symptoms. No yield reductions occurred when the tissue Zn levels were as high as 115 in the first and 57 μg g−1 in the fourth priming. The grade index of tobacco was not affected by Zn applications but B applications of 8.8 kg ha−1 significantly decreased the index. Tissue Zn and B were higher in the 1st and 2nd than in the 3rd, 4th, or 5th primings. Key words: Tobacco yields, tissue boron, tissue zinc, boron toxicity