By Sjef Lamers of Sustainable Nutrition
B. For. Sc., Dip. H.L.S. Dordrecht, MNZSSS
HGA newsletter, February 2009
Introduction
There are 16 essential nutrients required for plant growth: carbon (C), hydrogen (H), oxygen (O), nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), sulfur (S), iron (Fe), manganese (Mn), zinc (Zn), copper (Cu), boron (B), molybdenum (Mo), and chlorine (Cl). Of these 16 nutrients most are derived from the soil except carbon, hydrogen and oxygen.
Nature has provided the soil with a form of nutrient storage (a nutrient cupboard): very small clay and organic particles called colloids. These colloids have electrical charges: they are positively or negatively charged. The amount of these colloids in a soil determines the total amount of charges in a soil. Nutrients are electrically charged ions in the soil. A positively charged ion (called cations e.g. potassium or calcium) will attach itself to a negatively charged colloid. A soil with a small amount of negatively charged colloids will have a very limited capacity to store elements like potassium and calcium. A soil with a high amount of negatively charged colloids is able to store a large amount of cations. The amount of fertilizer to use depends on the storage capacity of the soil. There is no general fertilizer application which will be valid for all soils. Every property will require its own fertilizer program.
Important aspects to monitor in the soil are:
- pH and Buffer pH: soil acidity determines the growth and health of roots
- organic matter: plays an important role in soil structure, water and nutrient holding capacity, reservoir of organic nitrogen and other nutrients
- the major elements phosphorus, sulfur, calcium, magnesium, potassium
- the trace (or micro) elements boron, zinc, copper, manganese, aluminium and iron.
Soil analysis takes the guesswork out of making fertiliser recommendations and leads to more efficient nutrient management.
Nutrient content and pH vary with soil depth. We suggest to take soil samples from the main soil horizons. Sub soil samples tend to be taken while investigating the suitability of land for hazelnut growing. The analyses results of the sub soil will give information about any chemical imbalances.
Soil analyses of New Zealand top soils (0150 mm depth) frequently indicate low levels of potassium, boron, magnesium, zinc, relatively low pH levels and high aluminium levels.
Soil pH
Excessive soil acidity can reduce growth and yield of hazelnut trees. A large amount of New Zealand soils are naturally acidic with a pH generally in the range of 5 to 6. Soil pH can decline over time due to the acidifying effects of rain, plant growth, fertilization (nitrogen and phosphate fertilizers). Lime (or dolomite if magnesium is required) can be used to improve the pH of the topsoil. Some laboratories conduct a buffer pH or lime requirement test. This test determines how much lime should be applied to adjust the pH to a target level.
Potassium
Young hazels require potassium (K) for shoot and root growth. Mature hazels have a need for potassium for nut production. Soils with a low K level or a high Mg level require extra potassium. The amounts of available potassium, magnesium and calcium in the soil are interrelated; an excess of any one of them can cause deficiencies of the others.
Phosphorus
Phosphorus (P) deficiency has not been a problem in general in hazelnuts despite the low content of P in some soils. Several factors contribute to this: hazelnuts have a good ability to extract P from the soil, P is mobile in the hazel and crop removal of P is relatively small. Generally P fertilisation is not necessary, but if soil analyses indicate very low P levels you may consider a P application before planting. If the pH is very low or very high then the phosphate fertiliser should be applied close to the plant rather than broad spread. Lock up of phosphate can occur within 48 hours in these soils.
Nutrient functions
The functions different nutrients perform in the hazel are:
- phosphorus: root growth and flowering
- sulfur: quality aspects like aromatic properties
- calcium: soil structure, cell division
- magnesium: chlorophyll
- potassium: root, shoot and nut growth
- boron: bud development and nut quality
- zinc: leaf size, height growth
- copper: enzyme systems; please monitor build-up in the soil from fungicide sprays
- aluminium: toxic element for roots, interferes with phosphorus and magnesium uptake, antagonistic to calcium
- manganese: chlorophyll, flowering.
Sustainable Nutrition gives independent advice on soil and plant nutrition. We endeavour to help hazelnut growers to achieve optimal production of hazelnuts.
Sustainable Nutrition: PO Box 54, Wakefield 7052.
http://www.sustainablenutrition.co.nz/about-us/