Nutrient removal with harvest

Optimising fertiliser inputs to improve grower resource efficiency and reduce environmental risk requires an understanding of what nutrients are being removed from the orchard. Nutrient removal can be in the form of leaching, volatilisation, runoff and removal of fruit from the orchard. This study quantifies nutrients removed with fruit at harvest for a certain fresh weight of fruit allowing calculation of nutrient removal from orchards with different yields. Per 10 tonnes of fruit removed at an average 32% flesh dry mater an average of 32.7 kg of nitrogen (N), 4.8 kg of phosphorous (P), 51.1 kg potassium (K), 3.8 kg sulphur (S), 0.9 kg calcium (Ca), 2.6 kg of magnesium (Mg), 265 g boron (B), 71.6 g iron (Fe), 58.7 g zinc (Zn), 17.3 g manganese (Mn) and 24.4 g copper (Cu) was removed.

Regional differences in the nutrient removal for phosphorus, potassium, magnesium, iron and sodium were statistically significant, but small.

On orchards with higher tree nutrient status as measured by leaf sampling, fruit nutrient content tended to be higher for all nutrients except calcium.

The influence of fruit flesh dry matter on nutrient content could not be assessed as originally intended due to an error with the sample analysis. No strong influence of dry matter was observed across the range of fruit flesh dry matter in this study, which was 27.5 – 37.0%. Nutrient removal is expected to increase with increasing dry matter as seen in other studies.

No significant influence of rootstock was observed on fruit nutrient status but only one Astro (SR1) and three Dusa samples were assessed. Other studies have demonstrated that rootstock can influence nutrient uptake and so rootstock effect should be considered in any future fertiliser research.

This study presents a nutrient removal table that can be used to estimate nutrient removal at harvest from orchards in the main growing regions of New Zealand. It is recommended that future work to optimise fertiliser application should focus on nutrients lost to leaching, understanding the influence of fertiliser application volume and timing on utilisation and nitrogen mineralisation from organic matter vegetation in the orchard. Also, a check should be done to understand if early versus late harvest makes a material difference in nutrient removal to influence fertiliser planning.