New iron-based fertilizer proves a good supplement to iron fertilization

Prayon,a manufacturer of phosphate fertilizers, has developed a new iron-based fertilizer that has performed well in trials and offers the added benefit of being able to boost calcium absorption. Wim Voogt, a researcher in plant nutrition, soil and water at Wageningen UR Greenhouse Horticulture, has trialled the new iron-based fertilizer in a series of tests.

In the first test, he compared three forms of the new fertilizer against the standard iron chelate DTPA at a dose of 25μ mol of iron per litre. He then tested at a concentration of 15μ mol of iron per litre. The testing was conducted on hydroponic cucumbers, some with a low pH (5.2–5.8) and some with a high pH (6.4–6.8); in both cases, the trial ran from sowing to first crop (approximately six weeks).

In the first test involving the high dose, no difference in growth or yield was observed in the low-pH plants when using either the new or the standard iron products. In the case of the high-pH plants, those fed with standard DTPA showed a slight increase in growth and biomass. In the low-dose tests, growth in the high-pH plants was lower than in the low-pH ones with both fertilizers.

"The effect of the pH level and a lower iron concentration are characteristic of hydroponic cultivation in which higher levels of iron are required than with mineral wool", says Voogt of the apparently negative results. As expected, in both tests an analysis of the dry matter revealed that iron absorption in low-pH plants was higher than in those with a high pH level.

What was striking was that the iron absorption with the new fertilizer was greater than with DTPA. In the case of the low-pH plants, this difference was statistically reliable but with the high-pH ones it was little more than a trend. In Voogt's view, this could indicate that iron-based fertilizers deliver iron more efficiently than DTPA.

In both tests, some chlorosis was initially observed with all three of the iron-based fertilizers: small yellow flecks appearing on the leaves while the veins remain green. Chlorosis is a sign of iron deficiency. The effect was more pronounced in the second test and primarily in the high-pH plants. Plants treated with the iron-based fertilizers were more chlorotic than those fed with DTPA.

These first two tests would seem to prove that while the iron-based fertilizer works well, high pH values should be avoided.

In both tests, the researcher observed symptoms of leaf curl: The edge of the leaf dies back while the inside of it continues to grow, forming a sort of umbrella.

"Based on documentation and our own experience, we know that this condition is related to climate and is symptomatic of a form of calcium deficiency," said Voogt. "There are indications that the iron-based fertilizer promotes calcium absorption, which is beneficial."

Absorption and transport of calcium are a concern with all main crops. More and more growers are now switching to semi-covered cultivation.

Problems as regards transport of calcium to plants are generally due to climate and energy-saving measures.
"The main problem in plants which are deficient in calcium is resistance to evaporation, which destroys cells. This causes symptoms such as blossom-end rot, tip burn and leaf spot," Voogt said.

Voogt considers the new iron-based fertilizer a good supplement, not least in view of its positive impact on calcium absorption.

The first semi-field trials with substrate cultivation were conducted in Bleiswijk in autumn 2012. The results confirm those of the two initial tests. The pH of the drip water was kept at between 5.5 and 6.

A field trial with tomatoes will soon be commencing in the Netherlands, while a trial is already under way in Belgium, with the first fruits due to be harvested shortly.

The new fertilizer will be introduced midway through the year.