The effects of foliar and soil nutrient application strategies for improving fruit quality of Zesy 002 kiwifruit

Introduction

Fruit calcium deficiency may cause considerable economic losses in horticultural fruit crops. Although soil calcium deficiency is rare in nature, fruit calcium deficiency may develop even in orchard soils with sufficient calcium status.

There are many factors affecting calcium nutrition in fruit crops in the soil-root-fruit pathway including;

• Antagonism where ions such as potassium compete with and reduce the uptake of ions such as calcium at the root surface

• Low soil pH

• High rates of nitrogen and potassium fertilisation leading to excessive vegetative vigour and reduced rates of fruit transpiration (a major driving force for fruit calcium accumulation).

In addition, due to current practice, growers may experience limitations regarding calcium availability and uptake due to:

• The competitive effect of potassium fertilisation

• Comparatively low calcium fertiliser application rate

• Calcium displacement from the exchange sites due to high nitrogen fertilisation

• Calcium loss due to leaching by high rainfall events and the free draining profile of sandy loam orchard soils.

Kiwifruit firmness was significantly co-related with fruit calcium and leaf calcium concentration at harvest.  Increasing calcium nutrition may increase the cell wall integrity and improve fruit firmness. Other studies have also reported that increasing calcium nutrition enhanced fruit firmness in kiwifruit.

Spatial separation of soil-applied calcium and potassium fertilisers

Trials carried out in kiwifruit vines, using cultivar Zesy 002 grafted onto Bruno and Bounty rootstock, to ascertain the best way to apply calcium and potassium fertiliser to reduce antagonism and increase nutrient uptake.

Trial blocks included spatial separation for calcium and potassium fertilisers, where one fertiliser is applied to one side of the kiwifruit row and the other fertiliser is applied to the opposite side of the row, compared with no spatial separation of fertilisers (fertilisers applied together) and true control.

The fertiliser nutrient formulations used in the trials to supply nitrogen, calcium and potassium included; calcium ammonium nitrate, gypsum and sulphate of potassium.

Results from the spatial separation trials included a marked increase in the uptake of calcium in leaf tissues, vine and fruit as well as positively influencing fruit firmness at harvest when compared to the other trial blocks.

The uptake of potassium in root, leaf and fruit tissues was not affected by the spatial separation of fertilisers. It was noted there was no significant effect on the uptake of nitrogen and potassium and no uneven translocation or distribution of calcium and potassium in the kiwifruit leaf canopy. Also, regardless of which side of the canopy the nutrients are taken up by the roots, the subsequent translocation was integrated evenly throughout the vines.

This indicates that spatial separation of calcium and potassium fertilisers significantly avoided the antagonistic effect of potassium on the uptake of calcium ions in root tissue, increasing the translocation from root to leaf tissues.  

This suggests spatial separation of calcium and potassium fertilisers is an effective strategy in increasing calcium nutrition of horticultural crops, without reducing potassium supply, as kiwifruit vines have high potassium demand during the growing season.

These findings offer a simple technique that can easily be adopted by the kiwifruit industry to improve fruit post-harvest quality.

References

Effects of soil & foliar nutrient application strategies for improving fruit quality for 'Zesy002' kiwifruit (massey.ac.nz)