Abstract:
This greenhouse study investigated the effects of the addition of vesicular-arbuscular mycorrhizal (VAM) inoculum (Glomus mosseae [Nicol. & Gerd.] Gerdemann & Trappe and Glomus etunicatum Becker & Gerdemann) on capsicum (Capsicum annuum L. cv. Target), sweet corn (Zea mays L. cv. Snosweet), and tomato (Lycopersicon esculentum Mill. cv. Floradade) grown in a low P sandy loam (6 mg NaHCO3-extractable P/kg) with 5 rates of P (0, 10.3, 30.9, 92.7, or 278 mg P/kg oven-dry soil; P1, P2, P3, P4, or P5, respectively) and 2 rates of N (50 or 200 mg N/L in irrigation solution; N1 or N2, respectively). The growth periods (from sowing to harvest) for the 3 crops were as follows: 27 August-22 November 1993 for capsicum, 26 August-29 October 1993 for sweet corn, 31 August-22 October 1993 for tomato. For VAM-inoculated capsicum at PI, the dry weight (10.03 g/plant) and mean P concentration in the 5 youngest mature leaves (0.14%) were greater (P < 0.05) than those for uninoculated plants (0.28 g/plant; 0.09% P); a high coefficient of variation necessitated the use of log, transformed data to show differences. At low P rates, dry weight of sweet corn (P1, P2) and tomato (P1) plants colonised with VAM did not differ (P > 0.05) from uncolonised plants, despite inoculated plants having higher P concentrations in index tissues. At intermediate P rates, dry weights of inoculated plants were lower (P < 0.05) than those of uninoculated plants of sweet corn at P3 (81.1 and 102.2 g/plant, respectively) and of tomato at both P2 (11.7 and 34.5 g/plant, respectively) and P3 (39.6 and 52.1 g/plant, respectively). For all 3 crops, a lack of VAM response at high P ( >P4) was related to a lower (P < 0.05) VAM colonisation. The percentage root length colonised by VAM at P5 was only 6.8, 19.6, and 2.4% of that measured at P1 in the case of capsicum, sweet corn, and tomato roots, respectively. Increasing N concentration in the irrigation solution from 50 to 200 mg/L increased (P < 0.05) VAM colonisation of sweet corn (from 28 8 to 36 2%), but had no effect on capsicum and tomato.