Green Manure and Rice: Get Higher Rice Yields with Green Manure Crops

Backgrounder

Every farmer must think about how to get good yields, not only this season but year after year.  As rice grows, it takes nutrients out of the soil.  The crop uses about 20 kg nitrogen, 5 kg phosphorus, and 44 kg potassium to produce one ton of rice grain!  When no fertilizer is added and the rice yield is high, the soil is left poorer.  Rice yields will get lower and lower, unless you put these nutrients back into the soil.

One way to return nutrients to the soil is to use readymade chemical fertilizer.  But this is expensive and you may not always be able to get it when you need it.  What’s more, too much chemical fertilizer may harm the soil or pollute underground water.  You can also enrich the soil by using farmyard manure and compost made from kitchen and farm wastes.

These types of fertilizers improve the soil.  When they are added heavy clay soil will be less sticky and sandy soil will absorb more water and nutrients.

Another good low-cost way to keep the soil rich is to grow a green manure.  A green manure is a crop you grow and plough into the soil while still green especially to give nitrogen to the main rice crop.  Green manures also add other nutrients and organic matter to the soil.  You can plant the green manure before or after rice, when the land is vacant.  Let it grow until it is time to prepare the land for the next rice crops.  At this time, plough the green manure crop into the soil.  If you do this regularly, you will get free nitrogen for your rice crop, improve the soil by adding organic matter, and save money on fertilizer.

If you use green manure along with farmyard manure and compost, your soil will stay healthy and your rice yields will remain high.

Legumes are preferred green manure crops.  And if you grow food legumes such as cowpeas, kidney beans, mung beans, or soybeans – you can also use the seed as nutritious protein-rich food for your family.  Or you can plant a forage crop like clover or siratro to feed your animals.  After cutting three or four times for fodder, you can plough it under for green manure.  Forage legumes also keep the soil from being blown or washed away by wind and rain.

Certain stem nodulating legumes like Sesbania and Aeschynomene that can be grown either under dry or flooded soil conditions may also work well as a green manure for rice.

Such green manure crops can add about 55 to 60 kg of nitrogen per hectare to the soil.  This is like getting 55 to 60 kilograms of nitrogen fertilizer almost free of cost.  Some legumes add much more.  Because legume roots grow deep, they also bring up other nutrients from deep down in the soil where rice roots cannot reach.  These nutrients will feed the next rice crop.

Insect pests and diseases that attack legumes usually do not attack rice.  So you will get a healthier rice crop, with fewer diseases and pests, when you grow it after a legume crop.

If you cannot plant a green manure crop in the field for any reason, you can cut leaves and small twigs from trees or shrubs for green manure.  You can grow these trees or shrubs on field bunds.  On steep slopes plant hedgerows of trees such as leucaena or gliricidia across the slope.  These hedgerows keep the topsoil from washing away and they can give you fuelwood too.

Choosing the right green manure crop: Choosing the right crop is important when you grow green manure.  You should be able to grow it easily and without spending extra money on water, fertilizer, or pesticide.  Remember that a green manure crop should suit the soil, climate, and rainfall in your area.  It should be easy to sow, with readily available seed.  A green manure crop should grow fast and build up nitrogen quickly.  It should fit the time available between main crops so it does not delay the sowing of rice.  Also, it should resist pests and diseases, and be easy to plough into the soil.  When possible, choose a green manure crop that will also give you food, fodder, or fuel.

Summary: A green manure crop is a crop grown especially to provide nitrogen and other nutrients for the rice crop.  It also adds organic matter to the soil.  It is planted before or after rice, when the land is vacant.  Then it is ploughed into the soil as fertilizer for the rice.  Legumes make good green manure.  Many legumes can also give you food for your family and fodder for your animals.  Leaves and small twigs cut from hedgerows or perennial trees can also be used for green manure.  Although it can be a lot of work, it is usually worth the effort.  Growing a green manure crop can enrich your soil and keep rice yields high year after year.