ARABLE FARMING IN NEW ZEALAND OCCUPIES A LAND AREA OF JUST OVER 200,000 HA. THE MAJOR CROPS ARE THE CEREALS: BARLEY (56,000), WHEAT (53,000), MAIZE (20,000) AND OATS (10,000), AND THE VEGETABLES: POTATO (12,000), SQUASH (7,000) ONION (7,000), PEAS AND BEANS (8,000).
Gypsum to improve soil-structure
Arable land comprises many different soil types including some heavier soils that suffer structural problems that would benefit from applications of gypsum. However, as with pastoral agriculture, there is an economic barrier to the extensive use of gypsum to remedy these problems. The gross income obtainable with most arable crops is about NZ$2,000 /ha. After taking into account input costs of perhaps NZ$1,300 there is insufficient margin left to allow for the application of gypsum at rates sufficient to remedy soil problems (2-4,000 kg/ha @ NZ$300-600 /ha). This argument does not preclude the use of local high-rate applications of gypsum to help restructure the soil in problem areas such as around gateways.
Gypsum as a fertiliser
New Zealand soils are commonly sulphur deficient. There are situations where it is desirable to increase the sulphur content of a soil without increasing its phosphorous content (e.g. with superphosphate). In these circumstances a good case can be made for applications of gypsum as a sulphur (and calcium) fertiliser at rates of up to 1,000 kg/ha. Organic crops are a small but very fast-growing sector where superphosphate is not permitted. Here again, gypsum can be used as a calcium and sulphur fertiliser and should be applied at rates up to 1,000 kg/ha (at these low rates gypsum brings only a marginal soil-structure benefit).