Availability of phosphorus in greenhouse cropping systems with tomatoes – influence of soil and citric acid

Abstract

Analyses of plant sap from organic greenhouse tomato crops show that the levels of phosphorus (P) are frequently low, despite the fact that soil analyses indicate P status in the soil to be good. In the present study, two soils (A and B) with a pH just over 6 and a high total content of N and P were investigated with respect to release of P and uptake in a tomato crop. The fertilisers primarily used on soil A was silage and bloodmeal, and on soil B Vinasse and blood meal. An incubation experiment showed that the release of P per unit time was greater from soil A than soil B. This difference between the two soils may be due to lower soil organic matter concentration, with less P sorbed by Al and Fe on soil A, and a fertiliser regime which favours a high concentration of dissolved organic carbon in this soil. Tomato plants grown for 10 weeks in the soils had greater DW production, total uptake of P and concentration of P in the leaves on soil A than on soil B. Addition of citric acid to the soils in order to mobilise P increased plant yield and uptake of N and P on soil A. Despite the increased growth, the concentration of P in plant leaves increased and the N concentration was unchanged. On soil B addition of citric acid decreased Zn uptake in the tomato plants despite good availability, resulting in a lower concentration of this micronutrient in the leaves. The plants on soil A maintained their concentrations of all micronutrients analysed, but the ratio of P to micronutrients increased. Thus for commercial organic tomato growers, adding citric acid with the irrigation water offers a possibility to increase P availability.

Assessment of the Effect of Glycine, Oxalic Acid and Nitrogen-Phosphorus-Potassium (NPK) Fertilizer as Nutrient Supplement Using Phosphate and Oxalic Acid as Indices

“…This study evaluated the nutrient availability in soils treated with low molecular weight organic acid and amino acid -glycine and oxalic in comparison with standard fertilizer -NPK using oxalic acid and phosphate as indices. Several studies have established that plants excrete organic acids as adaptive response in nutrient deficient environment [1][2][3]5,7,16,17].…”

“…The increase in phosphate release by glycine and oxalic acid may also be due to the dissolution and desorption powers of low molecular weight organic acids [12]. The higher release of phosphate in oxalic acid can be attributed to its lower pH in solutions due to the presence of two carboxylic groups and its potential to enhance phosphorus availability in ecosystems while the lesser release of phosphate in glycine may be due to the fact that it is neutral in solutions [2,17,18]. NPK which released the least amount of phosphate can be attributed to the alkalinity of the soil which have must caused the conversion of phosphate in the fertilizer to tricalcium phosphate a form which is unavailable to the soil [19].…”

An insight into the role of the organic acids produced by Enterobacter sp. strain 15S in solubilizing tricalcium phosphate: in situ study on cucumber

“…These effects are produced by an increased P uptake at root level, that indeed results from OAs secretion by microbes and the P solubilizing property of such carboxylates [ 45 ]. Accordingly, citric acid (2.5 mM) supplementation in soil has already been shown to enhance P uptake and the yield of tomato plants [ 31 ]. On the contrary, the supply of OAs mixture severely inhibited the cucumber plant growth, suggesting a possible toxic effect maybe ascribable to the final OAs concentration.…”

“…However, stimulating effects on the metals acquisition have been usually reported at low concentrations of OAs, whereas, at high concentrations, OAs may cause phytotoxic effects [ 63 ]. For instance, the addition of citric acid with the irrigation water increased the concentration of Ni, Zn, Co, Cr, Mn, and Fe in leaves of Noccaea caerulescens [ 64 ], whereas the same OA decreased the concentration of Zn and Mn in tomato leaves [ 31 ]. Overall, these observations suggest that the modulations of plant ionomic signature in response to OAs application are dependent on concentration, strength, and type of OA type, as well as on plant species.…”