P. Adams

Diurnal variations in the oxygen content and acid requirement of recirculating nutrient solutions and in the uptake of water and potassium by cucumber and tomato plants

Abstract The oxygen content of recirculating nutrient solutions was measured in July and August, together with the amounts of acid required to maintain a constant pH in the solution and the rates of uptake of water and potassium. The oxygen content of the solutions declined to a minimum during the brightest part of the day. The oxygen deficit was highly correlated with both the temperature and the amount of acid required to maintain the pH of the nutrient solution. Under similar environmental conditions, the oxygen content of the solution was reduced to lower concentrations by cucumber (2.7 mg l−1; 34% saturation) than by tomato plants (6.7 mg l−1; 84% saturation), reflecting the thicker root mat formed by cucumber.

Tomato yields in relation to the nitrogen, potassium and magnesium status of the plants and of the peat substrate

SummaryThe effects of 96 combinations of nitrogen, potassium and magnesium were studied in four tomato crops grown in peat. Yield responses were found to each of these nutrients. In a late-planted crop, nitrogen also increased the early yield.The nutrient contents of the leaves corresponding to maximum yield were 4.5–5.1% N, 4.4–5.6% K and 0.31–0.40% Mg.Yields increased with applied nitrogen until the peat contained 45–65 mg N/l and decreased at concentrations above 70 mg N/l. Maximum yields were achieved in two of the crops when the peat contained 330–430 mt K/l; in the other two crops 100 mg K/l sufficed, though this was insufficient for high quality fruit. A magnesium content of 250 mg Mg/l was fully adequate.A high proportion (>90%) of the extractable potassium in the peat was water-soluble, thus making a major contribution to the overall salinity.

Some Responses of Lettuce, Grown in Beds of Peat, to Nitrogen, Potassium, Magnesium and Molybdenum

SummaryThe effects of 96 combinations of N, K and Mg were studied in three crops of lettuce grown in peat; there were two sources of N, Nitrochalk (26% N) and sulphur-coated urea (32% N), and molybdenum was included as an extra factor in one crop. The yield and proportion of hearted lettuce increased with applied N until the peat contained 60 mg N I-1. In two crops higher N concentrations were unfavourable, due to increased acidity in the peat which resulted in greater uptake of Mn by the plants. The yield and the proportions of both hearted and of marketable lettuce declined as the Mn content of the leaves increased. In the third crop, which was not affected by Mn toxicity, there was little response to N over the range 60–250 mg N I-1. The yield and quality of the produce improved with increasing K until the peat contained 200 mg K I-1, but concentrations of up to 600 mg K I-1 had little further effect. The N and K contents of the leaves corresponding to maximum yield were 5% N and 8% K. There was no res...

Some effects of micronutrients and liming on the yield, quality and micronutrient status of tomatoes grown in peat

SummaryThe effects of a fritted micronutrient mixture on the growth and yield of tomatoes were studied in relation to the pH of the peat substrate. The treatments consisted of three rates of application of the fritted micronutrient mixture (0, 200, 500 g/m3 F 253A) in factorial combination with four rates of liming (average pH values 4.5, 5.1, 5.8 and 6.7).Three crops were grown to maturity, and in each case the total yield of fruit decreased (18–24%) when the peat was limed to pH>6.0 (P<0.001). Omission of the micronutrient mixture reduced the yield by 20–65% (P<0.001). The combination of heavy liming and omission of micronutrients was particularly detrimental, and depressed the yield by 40–87% as compared with the most favourable treatment. The incidence of ripening disorders was also increased by heavy liming and by omission of micronutrients. The boron, copper, iron, manganese and zinc contents of the leaves are tabulated. Multiple regression analyses suggested that the yield was consistently depressed by deficiencies of boron and copper, and responses to iron and manganese were also found.

Some responses of cucumber, grown in beds of peat, to N, K and Mg

Two levels of N and four levels of K, applied to beds of sphagnum peat before planting (Experiment A), were tested in factorial combination with three concentrations of N (50, 175 and 300 mg 1-1) and two of K (50 and 250 mg T1) in the liquid feed. In three cucumber crops grown, Mg was supplied or omitted before planting as a split plot factor (96 subplots). In two further crops (Experiment B), grown in fresh peat, six concentrations of N (20-320 mg 1-1) were tested in the liquid feed, all other nutrient levels being constant. In Experiment A, the early yield was reduced by low and high levels of N. The main effect of N on the final yield was not significant, but maximum yield was achieved with 175-300 mg 1-1 N in the liquid feed where the peat received a small amount of ureaformaldehyde (15 g m“2) and Mg fertilizer. The N x Mg interaction became increasingly marked with successive crops; the loss in yield due to Mg deficiency (<31%) increased with the amount of N applied. K deficiency reduced the yield by...

Effects of copper deficiency and liming on the yield, quality and copper status of tomatoes, lettuce and cucumbers grown in peat

Abstract Tomatoes, lettuce and cucumbers, grown in beds of peat, received 3 levels of copper sulphate (0, 0.5 and 5 g/m2) in factorial combination with 2 rates of liming (average pH values 6.5 and 6.9). Omission of copper resulted in copper deficiency and decreased the yield of tomatoes, lettuce and cucumbers by 11% (P 7 μg/g).

Some effects of micronutrients and liming on the yield, quality and micronutrient status of lettuce grown in beds of peat

SummaryThe effects of a fritted micronutrient mixture on the growth, yield and quality of winter lettuce were studied in relation to the pH of the peat substrate. The plants were grown under glass and the atmosphere was enriched with CO2 to 1000 vpm. The treatments consisted of three levels of the micronutrient mixture (0, 200 and 500 g m−3 F 253A) in factorial combination with four rates of liming (average pH values 5.cv 1, 5.6, 6.5 and 7.2). Responses to the omission of individual micronutrients (B, Cu, Fe, Mn, Mo or Zn) at pH 6.7 and the interaction between molybdenum level and pH (4.9 and 6.9) were also studied. The omission of the micronutrients caused a marked depression in the yield; few of the lettuce hearted and the leaves had low Cu contents (2 μg g−1) irrespective of pH. At pH 5.0 the Mo content was very low (0.15 μg g−1) and pH > 7.0 reduced the Mn content to 18–22 (μg g−1. The yield and proportion of hearted lettuce were also reduced at pH 5.0–5.2 by the application of micronutrients at 200 a...

Some responses of cucumber, grown in beds of peat, to micronutrients and pH

SummaryThe effects of omitting individual micronutrients on the growth, yield and quality of cucumbers were studied. In the first experiment, omission of Cu and B reduced the yield by 93% and 70% respectively in new peat, and by 56−100% and 0−23% respectively in subsequent crops. Omission of Fe reduced the yield only in new peat (18%) and there was no response to omission of Mn, Mo or Zn. In the second and third experiments, omission of Cu reduced the yield by 80−95% irrespective of pH (5.2 and 6.2). Omission of B reduced the yield by 59% at pH 6.2 but had little effect at pH 5.2. In the third experiment, there was no response to omission of B at pH 6.1. The proportion of Class 1 fruit was always reduced by omission of Cu and, to a lesser extent, by omission of B. Severe deficiencies of Cu and B were associated with 2 µg g−1 Cu and 7−16 µg g−1 B in the leaves.

Some effects of micronutrients and liming on the production and quality of glasshouse carnations grown in a peat-sand substrate.

Responses to three levels of a fritted micronutrient mixture (0, 200 and 500 g m-3), applied in factorial combination with four rates of liming (average pH values 4.3, 5.1, 6.5 and 7.0), were studi...