Crop Rotation: Which Crop After Which, and Which to Never Repeat

This is the rule that matters most, and the one most often broken without realising it. The pathogens that do the worst damage — wilts, root rots, nematodes — live in the soil and are host-specific. They build up under a crop and collapse without it. Plant the same family again and you are feeding the population you are trying to fight; plant something unrelated and it starves.

The trap is that family is not obvious from the plate. Tomato, potato, brinjal and chilli are all nightshades and share bacterial wilt and early blight, so brinjal after tomato is very nearly tomato after tomato. Cotton and bhindi are both mallows. Mustard, cabbage, cauliflower and radish are all crucifers. Learn the families and half the rotation problem solves itself.

Crops differ in how hard they draw on the soil. Cotton, maize, wheat, sugarcane and cabbage are heavy feeders, particularly of nitrogen. Root crops such as onion, garlic, carrot and radish are lighter. Legumes are the only group that gives back: with the right Rhizobium bacteria on their roots they fix nitrogen from the air, and a good share of it stays in the soil for the crop that follows.

So the pattern that works almost everywhere is heavy feeder, then light feeder or legume, then back. Chana after cotton, wheat after moong, maize after groundnut — each of those hands the next crop nitrogen you did not have to buy. The saving is real and it compounds, because soil that is not being mined every season holds structure and organic matter better.

Two cautions, because this is where enthusiasm overshoots. A legume does not replace your whole nitrogen requirement — it reduces it, and by how much depends on the crop, the nodulation and whether you removed the residue. And a legume still counts as a family: groundnut after chana is a legume following a legume, which breaks Rule 1 even though both are 'good for soil'.

Crops draw water and nutrients from the depth their roots reach. Cotton, castor, tur and sugarcane go deep; onion, wheat, most vegetables and the millets stay shallower. Run the same rooting depth season after season and you exhaust one layer while another sits unused, and you encourage a compacted pan at plough depth.

Alternating fixes both. A deep-rooted crop opens channels the following shallow crop uses, brings up nutrients that had leached below reach, and helps break compaction without machinery. This is a slower benefit than the nitrogen one, and it is the reason a long rotation beats a two-crop cycle even when both crops are from different families.

Rotation choices narrow by soil, and pretending otherwise wastes a season. The three broad situations most Indian farmers are in are below. If you do not know your soil's texture and organic carbon, a soil test costs little against a season of the wrong crop — reading a Soil Health Card explains the figures.

Chemical-free growing fails most often for a simple reason: the farmer removes the spray but keeps the rotation that made the spray necessary. Rotation is not a nice extra alongside organic practice — it is the mechanism that makes it work. Break the host cycle and the disease pressure falls before any input decision is made.

The same is true of fertility. A legume in the rotation, residue returned rather than burned, and green manure in a fallow gap will together carry a large part of the nitrogen requirement. That is not a claim that you can drop all inputs; it is the reason organic systems that rotate seriously succeed while ones that simply stop spraying do not. Improving soil health naturally covers the organic matter side, and integrated pest management covers what to do about the pressure that remains.

One honest caveat, because it decides whether the plan survives contact with the year: the best agronomic rotation is worthless if you cannot sell the crop. Check that a buyer or a procurement centre exists for the break crop before you commit the field to it, not after.

A rotation is a multi-season plan, and the reason most rotations fail is that nobody wrote down what was in which plot two seasons ago. Recording crop, plot, sowing date and inputs as you go is what makes the family rule enforceable — keeping a farm record covers the habit, and the app does the same job with the dates filled in automatically.

The cost and profit calculator is worth running before you switch: a break crop often shows a lower gross return and a better net one once the saved fertiliser and spray are counted, and that comparison is the argument for rotating. It needs no account.

What we will not do is tell you the dose or the variety. Those come from your state package of practices or your KVK, because they change by region and season. And nothing here replaces knowing your own field — the rules above are the frame, not the answer.