Crop rotation is the procedure of growing different crops successively on the same plot of land instead of growing the same crop on the same land year after year . This results in a number of benefits :-
A) As each crop takes or returns different nutrients to the soil it prevents or minimises the drain of nutrients on the soil so maintaining soil fertility . By crop rotation , mulching and adding compost regularly to the soil artificial fertilizers become unnecessary . B) It prevents a build-up of pests and diseases which will attack a crop when it is grown year after year in the same ground .
A good plan for crop rotation is as follows :-
I. Root crops to start - eg potatoes , carrots , parsnips , turnips or onions . Root crops break up the soil and bring deeper soil nutrients to the surface .
II. A legume crop , eg beans (in summer) or peas (in winter) . Legume crops fix their own nitrogen ( an essential plant nutrient ) from the air so when the root system decays the nitrogen remains for the next crop .
III. A leaf crop , eg lettuce , silver beet , spinach or cabbage . Leaf crops require a lot of nitrogen to produce a good yield of edible leaves so they make use of the nitrogen left behind by the legumes .
IV. Other crops such as capsicum , tomatoes , cucumber , broccoli or any others which do not fit into groups I. to III. above . Alternatively the fourth part of the rotation can be to leave the ground fallow to grow volunteer weeds which can then be dug under ( BEFORE flowering and setting seed ) to provide organic matter for the next crop .
THE ROTATION THEN STARTS AGAIN .
Mulching is the practice of forming an organic layer on top of the soil around the plants , even over the entire vegie patch. This organic layer has a number of effects on the soil and plants in the surrounding area :
1. It keeps the soil surface cool in summer allowing micro-organisms to function at the soil surface and continue to breakdown organic matter and release nutrients . 2. It conserves moisture - A very important point in times when water may be in very limited supply . A mulch as well as reducing evaporation from the soil surface also increases the proportion of the soil water present in the plant root zone , where it counts . 3. Weeds are suppressed - This reduces or eliminates the need for cultivation or worse yet , pulling out the little buggers by hand . This is an important point because weeds will compete with your crop for light , nutrients , water and space and in so doing can seriously reduce crop yields . 4. Nutrients are released by the breakdown of the mulch so that the vegies are have a built in , time release food source . The organic matter when incorporated into the soil will also improve soil structure an therefore fertility . 5. The surface of the soil under the mulch is not compacted by rain drops so water runoff is reduced and infiltration of rain correspondingly increases . By the same token if rainfall is high and drainage not what it should be , mulching can contribute to waterlogging of the soil so keep an eye out for this.
Some materials used for mulching -
a) Compost - Ideal . b) Hay or straw - Ideal . c) Grass Clippings - Can tend to form a water impermeable layer so they should be mixed with sawdust of compost prior to use . d) Dry leaves - Can also form an impermeable layer so should be shredded or mixed with other material prior to use . e) Sawdust and wood shavings - Radiata pine material is not suitable as a mulch . f) Animal manures - should be old and well rotted down before use or they can burn the plants .
This is the process of growing a crop on your vegie patch and then digging it in to provide organic matter. This is a good idea when you are opening up a new area or as part of a crop rotation. The most value is obtained by using a legume eg peas, beans, clover, or lucerne which fixes nitrogen at the same time, releasing it to the plants as it breaks down. At least two weeks should be allowed between turning in the green manure and planting vegies to allow the green manure some time to break down. The green manure should also be turned in before it flowers so it is at a succulent stage of growth and will break down earlier and no seed is set to come up as a "weed" later.