Understanding CA Module 3 Soil Cover

Soil cover A good farmer gives her soil some cover to keep it healthy. Only a healthy soil can produce a good crop

The soil should always be covered

Types of soil cover There are two main types of soil cover Living plant material Crops and cover crops Mulch or dead plant material Crop residues and prunings from trees and shrubs

Cover crops These are crops grown to cover the area between rows of commercial crops or to cover the whole field when no commercial crop is growing. While commercial crops have a market value, cover crops are mainly grown for their effect on soil fertility or as livestock fodder.

Benefits and challenges of the use of cover crops Protects the soil Maintain N in organic form (less leaching) Control weeds Add OM to the soil Can solve compaction problems Increase porosity and internal drainage Challenges Some may require higher level of management Decomposition of CC can lead to deficit of N at the beginning of the growing season

‘Green manure crops’ vs ‘Cover crops’ Mainly legumes Mainly for N addition to the soil Incorporated into the soil at certain growth stages Cover crops Species from different plant families eg grasses, legumes etc Grown for specific plant attribute Grown to cover soil and feed soil organisms Mostly no market value like commercial crops

Some common cover crops Cajanus cajan – Pigeon pea Canavalia ensiformis – Jack bean -Dolichos lablab – Lablab bean Mucuna pruriens – Velvet bean Vigna unguiculata – Cowpea List local ones

Considerations before choosing a CC Multiple benefits Compatibility with cropping system Time of sowing and growth cycle Ease of management Water requirement – drought resistance Possibility of becoming a weed

Residue management Properly managed Badly managed Adds OM to the soil Retains C in the soil Buffers soil pH & facilitates availability of nutrients Captures rainfall Reduces evaporation & increase soil moisture content Badly managed Provokes uneven drying of soil Interferes with seeding &fertilizing activities Hinders the emergence of crop seedlings Allows weed species to emerge

Time of management of the CC Important to know because Most species can regenerate when interrupted prematurely Mature seeds can germinate and cause problems as weeds Most CC species at full flower = maximum accumulation of biomass Legumes – 1st pod formed but not yet matured Grains – milky stage Woody species (eg. Cajanus) – just before flowering because of wood development

How to manage the CC For long term soil cover from dead mulch Knife roller Chain Herbicide For immediate decomposition to release nutrients Slashing Mowing

Time of sowing the commercial crop Period between slashing/management of the CC and seeding of the commercial crop defines the production level of the crop. Related to allelopathy & N immobilization. For direct seeding over the CC, allow 8 to 12 days for CC with low to medium C/N ratio (C/N of 12-22) eg. legumes 12 to 20 days for CC with high C/N ratio (C/N of >24) eg. grasses

Cover crop seed production Initial source Research institute, extension service, other farmers or from the wild Produce just above 12-20% of the quantity needed. Reserve a specific site on-farm for seed production only. Produce more than one specie to spread risk

Challenges for maintaining soil cover Semi-arid areas Little rain so crops, shrubs,& trees produce less residue. Farmers also need them for feed, fuel wood or building. May be impossible to maintain soil cover for the whole year. Best to depend on crop residue, and prunings from trees and shrubs as the main source of soil cover. Diseases and pests May attack the CC and may therefore require special attention. Farmers often use fire to destroy pests and diseases. Rotate crops rather than burning to control pests and diseases. Consider using pesticides if necessary.

Challenges for maintaining soil cover Rats A dense CC may encourage rats which may attack the crop Slash the live CC as close to the ground as possible before planting. Baits/traps can be used Rotate crops to interrupt their food supply and disturb their living conditions Termites Many farmers report of soil cover attracting termites Termites are important. They break plant material on the surface and carry it into the soil to add to soil OM. By so doing, they aerate the soil and improve infiltration Most termites are beneficial. Only a few attack crops. They may eat the stem or damage the grain. This normally happens towards harvest time. Leave plant materials (mulch) on the surface so the termites attack this rather than the crop itself.

Challenges for maintaining soil cover Fire Bushfires or uncontrolled fires can spread into a CA field and destroy its soil cover. Leave a buffer zone around the field. Once many farmers in the area begin to practice CA, burning will be minimized. Education and bylaws are needed to reduce damage by uncontrolled fires. Livestock Uncontrolled grazing destroys soil cover Prevent animals by planting living fences, spraying field boundaries with cattle urine or planting CC not eaten by cattle around the farm. Fodder production and community agreed grazing area.

The value of mulch Understanding CA = understanding the value of mulch

Understanding the CA system Farmers that have not yet understood the importance of an adequate mulch cover have not yet understood the CA system