Soil and Pulses: A Symbiosis for Life, Paper delivered to mark World Soil celebration day at ARCN , Abuja by PROF. LATEEF BAMIDELE TAIWO Institute of Agricultural Research & Training, Obafemi Awolowo University, Ibadan

Soil and Pulses

Introduction

·         Nigeria’s biggest economic sector is agriculture

·         It accounts for 24% of GDP

·         Over 70% of informal sector jobs in the economy are related to rural agriculture (CBN).

·         One of the groups of crop that is commonly cultivated in Nigeria is the Pulses.

·         Pulses are annual leguminous crops yielding between 1 and 12 grains or seeds of variable sizes, shapes and colors within a pod

They are used for both food and feed

·         Pulses are a vital source of plant protein and amino acids for people around the globe

·         It is recommended that they should be eaten as part of a healthy diet to address obesity as well as to prevent and help manage chronic diseases such as diabetes, coronary heart conditions and cancer

·         They are also an important source of plant protein for animals. 

·          

Production Constraints

·         Optimum yields of the Pulses are dependent on many factors which include rainfall pattern, sunlight, moisture and soil types.

·         The soil factor is critical in the production of pulses

·         Poor soil affects crop yield especially if proper soil types are not chosen for these crops

·         This can lead to crop failure and food insufficiency in the country.

 The failure of previous efforts to achieve self-sufficiency in pulse production in Nigeria may be partly due to the neglect of the soil factor. 

•      The major constraints  include

Ø  Low inherent fertility and nutritional imbalance

Ø   Soil compaction

Ø   Erosion

Ø   Crusting and surface seal

Ø   Low water-holding capacity and drought

Ø  Reduction of pore spaces and infiltration rate

Ø   Low water-holding capacity

Ø   Accelerated run-off resulting in severe erosion

Ø   Decline of soil organic matter (SOM)

Ø   Decrease in pH

Ø   Nutrient imbalance.

Ø   Leaching of essential plant nutrients out of the root zone which is very severe in eastern Nigeria.

•       This calls for a management strategy capable of sustaining the potential yields of crops under intensive use of the soil.

Institutional Efforts

•       The United Nations declared 2015 as International Year of Soil (IYS).

In the UN report, released on 4^th December, 2015,

•       It was claimed that the world's soils are rapidly deteriorating due to soil erosion, nutrient depletion, loss of soil organic carbon, soil sealing and other threats,

•       The UN believed this trend can be reversed provided countries take the lead in promoting sustainable management practices and the use of appropriate technologies,

Soil Resources of Nigeria

•       Nigeria is blessed with various soil resources

•        According to Nicholaides III et al. (1984); Ogunkunle, (2010); and Esu,  (2005) at least six (6) of the soil orders of the USDA Soil Taxonomy have been encountered in Nigeria.

•      They include:

v  Alfisol

v  Ultisol

v  Entisol

v  Inceptisol

v  Vertisol

v   Andisol

•       According to WAAPP Strategic Soil Fertility Document (Unpublished), Alfisols and Ultisols together constitute about 65% of the soils in Nigeria.

They are deep to fairly deep soils with loamy sand/sandy loam surface increasing in clay content with depth to sandy clay loam/sandy clay or clay.

The two soils occur both in the savanna and rainforest regions.

•       Entisols constitute about 15% and Inceptisols about 10% of the soils in Nigeria {Ofomata (1975); Esu (2005)}.

•        Entisols are less developed than Inceptisols. Both of them occur on all the parent materials and vegetation units particularly in sand dunes, coastal deposits and flood plains in lower slopes or valley bottom positions in the toposequence.

•       Most of these soil types are suitable for the cultivation of pulses

Soil as a complex resource

•       Soil makes up the outermost layer of our planet and is formed from rocks and decaying plants and Animals.

•       Soil has varying amounts of organic matter (living and dead organisms), minerals, and nutrients.

•        • An average soil sample is 45 percent minerals, 25 percent water, 25 percent air, and five percent organic matter.

•        Different-sized mineral particles, such as sand, silt, and clay, give soil its texture. • Topsoil is the most productive soil layer. •

•       Ten tonnes of topsoil spread evenly over a hectare is only as thick as a one coin. •

•        Natural processes can take more than 500 years to form 2 centimeters of topsoil.

•        In some cases, 5 tonnes of animal life can live in one hectare of soil.

•       Fungi and bacteria help break down organic matter in the soil.

•       • Earthworms digest organic matter, recycle nutrients, and make the surface soil richer.

•       • Roots loosen the soil, allowing oxygen to penetrate.

•       This benefits animals living in the soil. They also benefit roots which require oxygen themselves. They further hold soil together and help prevent erosion.

•       A fully functioning soil reduces the risk of floods and protects underground water supplies by neutralizing or filtering out potential pollutants and storing as much as 3750 tonnes of water per hectare.

•       • Scientists have identified several types of soil in Europe, United States   and Nigeria.

•       • Soil stores 10% of the world's carbon dioxide emissions.

Soil management strategies

• Some of the soil management strategies include

Ø   Fallow systems

Ø   Cover cropping

Ø   Farm yard manuring

Ø   Green manuring and

Ø   Use of nitrogen-fixing plants

Ø  Crop rotation is used to control pests and diseases that can become established in the soil over time.

Ø  The changing of crops in a sequence decreases the population level of pests by

Ø   (1) interrupting pest life cycles and

Ø   (2) Interrupting pest habitat.

•       Some of these soil management techniques lead to the replenishment of nutrient loss in soils especially nitrogen

Forms of nitrogen in soil

•      All plants are able to take up nitrogen from the soil in the form of ammonium (NH4) or nitrate (NO3-)

•       Together, these are known as available nitrogen (N).

•       In addition to taking up available N from the soil, legumes (clovers,  medics, peas and beans (Pulses)) are also able to acquire N from the abundant supply in the atmosphere via special soil bacteria (rhizobia) which are housed in nodules on their roots.

•      With fully functioning nodules, legumes can grow in soils that are deficient in available N.

•      These rhizobial ‘factories’ are subject to variation in establishment and performance and so a supportive environment must be provided to maximise N₂ fixation

•      Of all the essential nutrients, nitrogen is required by plants in the largest quantity and is most frequently the limiting factor in crop productivity

•      In plant tissue, the nitrogen content ranges from 1 to 6%.

•      Proper management of nitrogen is important because it is often the most limiting nutrient in crop production and easily lost from the soil system

Forms of nitrogen available for plant uptake and functions of nitrogen in plants

•      They are mainly ammonium and nitrate

•      Nitrogen is an essential element of all amino acids

•      Amino acids are the building blocks of proteins

•      Nitrogen is also a component of nucleic acids which form the DNA of all living things and holds the genetic code

•      Nitrogen is a component of chlorophyll which is the site of carbohydrate formation (photosynthesis)

•       Chlorophyll is also the substance that gives plants their green colour

•      Photosynthesis occurs at high rates when there is sufficient nitrogen

•      A plant receiving sufficient nitrogen will typically exhibit vigorous plant growth.

•      Leaves will also develop a dark green colour

Consumption of nitrogen by plants and other organisms (Nitrogen cycle)

•      Nitrogen is a very dynamic element

•      It not only exists on earth in many forms but also undergoes many transformations in and out of the soil

•      The sum of these transformations is known as the nitrogen cycle

•      Though complex, the nitrogen cycle helps us to understand the complex relationships that exist among the many forms of nitrogen

•       The nitrogen cycle also provides us with insight pertaining to the availability of ammonium and nitrate which are the only nitrogen forms useable by plants

Table 1: Various forms of nitrogen

Mineralization

•      Mineralization in soil science is decomposition or oxidation of the chemical compounds in organic matter into plant-accessible forms.

•       Whether nitrogen is mineralized or immobilized depends on the C/N ratio of the plant residues^.

•      In general plant residues entering the soil have too little nitrogen for the soil microbial population to convert all of the carbon into their cells.

Nitrogen fixation

•       Although atmospheric nitrogen gas (N₂) makes up approximately 78% of the air, it cannot be directly used by plants

•       Instead, atmospheric N₂ only becomes available to plants through three unique processes

•       The final product of each of these processes is ammonium which is then available for plant uptake

•       The three processes which convert atmospheric nitrogen to ammonium are :

•           biological nitrogen fixation

•           chemical nitrogen fixation

    atmospheric addition

Biological nitrogen fixation

•       Approximately 80% of the atmosphere is nitrogen gas (N₂)

•       Unfortunately, N₂ is unusable by most living organisms

•       Plants, animals and micro-organisms can die of nitrogen deficiency surrounded by N₂ they cannot use.

•       All organisms use the ammonia (NH₃) form of nitrogen to manufacture amino acids, proteins, nucleic acids and other nitrogen-containing components necessary for life.

•       Biological nitrogen fixation is the process that changes inert N₂ to biologically useful NH₃.

•       This process is mediated in nature only by bacteria.

•       Other plants benefit from nitrogen-fixing bacteria when the bacteria die and release nitrogen to the environment or when the bacteria live in close association with the plant.

•       In legumes and a few other plants, the bacteria live in small growths on the roots called nodules.

•       Within these nodules, nitrogen fixation is done by the bacteria and the NH₃ produced is absorbed by the plant.

•       Nitrogen fixation by legumes is a partnership between a bacterium and a plant.

•       In addition, certain soil organisms have the special ability to convert atmospheric nitrogen to ammonium

•       These organisms include several species of bacteria, actinomycetes, and cyanobacteria

•       In the soil, nitrogen-fixating organisms can form special relationships with plants called “symbiotic” associations

•       Symbiotic is a term that means “living together.”

•       Although a symbiotic relationship can be antagonistic, the symbiosis that occurs during biological nitrogen fixation is generally mutual and beneficial

The biochemical mechanism of N₂ fixation can be written in simplified form as follows:

Biological Nitrogen Fixation Management Programme

•       The occurrence of the symbiotic relationship is heavily dependent upon a variety of soil conditions

•        If a program incorporates nitrogen fixation, the following considerations can determine your success

•        First and foremost, the rhizobium must be compatible with the legume

•       If your crop is rhizobium-specific, you must use the correct rhizobium species

If the inoculum (which contains the rhizobium bacteria) is applied to seeds, the procedures must be properly follow

•       Nitrogen fixation takes place when total soil nitrogen is insufficient

•       When sufficiently present, the plant will instead rely on the nitrogen available from the soil

•       Rhizobia are sensitive to any growth factor that limits root development

•       Such conditions as aluminum and manganese toxicities will limit inoculation.

•        Rhizobia are influenced by mineral nutrient imbalances

•       Low levels of calcium, phosphate, molybdenum under acidic conditions will limit nitrogen fixation.

•       Under alkaline conditions, phosphate, cobalt, boron, iron and copper levels become a concern.

•        Any growth factor (such as light, water, temperature stresses or soil compaction)

•       Any management factor (such as nutrient management, salinity) that detrimentally affects growth of the legume will detrimentally impact nitrogen fixation

Table 2. A summary of biological nitrogen fixation measurements by different legumes.

Table 3: Nitrogen derived from atmosphere (%ndfa) by soyabean cultivars as influenced by Bradyrhizobium inoculation (Daramola and Taiwo 1999)

 Amount of nitrogen fixed by legumes

•      When nitrogen is converted to ammonium during biological nitrogen fixation, ammonium becomes available to the legumes and the microorganisms that fixed it. Typically, the bacteria can fix anywhere between 20 and 80% of the total legume N

•      Small amounts of ammonium can also be released by roots of the legumes into the rhizosphere or the surrounding soil

Free-Living Nitrogen Fixation

•      “Free-living” nitrogen fixating organisms are also capable of nitrogen fixation but they are not associated with any plant species.

•       Examples of these organisms are Azotobacteria, Azospirillum, Clostridium and Pseudomonas

•      However, free-living species do not contribute largely to agricultural production

How much N do legumes contribute to following crops?

•      At maturity, 30 – 40 % of the N in legume crops is in the seeds which are typically 25 – 30 % protein

•      When the grains are harvested, much of the N that has been fixed will be exported off of the property

•      The N remaining in the shoot and root residues means that legumes usually make a positive contribution to soil N reserves

•      Research shows that yields of non-legume crops can increase when following a legume rotation.

•      It is believed that legume rotation increases the N content of soil thus making it an effective nutrient management strategy

•      However, when the legume is incorporated into the soil, the major benefit of the legume rotation lasts only during the first year following the legume rotation.

•      A healthy and productive field pea crop could fix up to 200 kg N/ha.

•       Soyabean (Glycine max) fixes between 59 - 70% of its nitrogen nutrition (Daramola and Taiwo, 2006)

Some misconceptions on the concept of Nitrogen transfer

•      However, the amount of nitrogen returned to the soil during or after a legume crop can be misleading

•      Almost all of the nitrogen fixed goes directly into the plant

•      Little leaks into the soil for a neighbouring non-legume plant

•      However, nitrogen eventually returns to the soil for a neighbouring plant when vegetation (roots, leaves, fruits) of the legume dies and decomposes

•      When the grains from a grain legume crop are harvested, little nitrogen is returned for the following crop

•      Most of the nitrogen fixed during the season is removed from the field

•      The stalks, leaves, and roots of grain legumes such as soyabeans and beans contain about the same concentration of nitrogen as found in non-legume crop residues.

•      In fact, the residue from a corn crop contains more nitrogen than the residue from a bean crop simply because the corn crop has more residues

•      However, it has been proved that nodule senescence contributes a substantial amount of nitrogen to soil

Contributions to human nutrition

•      In many countries, human nutrition is highly dependent on grain legumes for protein

•      There is a marked consumer preference for various seed types, for instance, some groups prefer the black form of the common bean whereas others favour the navy or kidney bean

•      The nutritional differences among these are not great so preference is based on custom (as are cooking methods that reduce anti-digestive activity) and the local adaptation of specific legumes.

•      There are more than 13,000 described species of legumes

•       Of the approximately 3,000 species examined, more than 90 percent form root nodules (in which nitrogen fixation presumably occurs in symbiosis with rhizobia)

•      Because few have been exploited for food, there is the prospect that the utilisation of legumes could be expanded substantially

•      Examples of these legumes are listed as follows:

•      IAR&T has also bred improved varieties of cowpea such as the popular Ife-Brown, Ife BPC and ART 98-12.

•      Nigeria and Niger produce 850, 000 and 271,000tones, respectively on annual basis. Cowpea, is the most widely cultivated food legume in semi-arid West Africa.

•      Nigeria harvests 4.5 million hectares annually.

•      Similarly and in collaboration with IITA, a number of improved  Tropical Glycine max (TGX) varieties of Soybean were bred.

•      This has led to substantial increase in yield and qualities of these crops.

•      Nigeria presently produces about 500,000 MT of Soybean annually making it the largest producer of the product on the African continent.

•       Soybean is a legume which is produced in most the middle belt of the country with Benue state accounting for about 45% of the total production in country (IITA Bulletin)

•      Soybeans are an important source of high quality and inexpensive protein and oil.

•      With an average protein content of 40% and oil content of 20%, soybean has the highest protein content of all food crops and is second only to groundnut in terms of oil content amongst food legumes.

•      Soybeans are used in the production of milk, edible oil and animal feed.

•      It’s high protein content and price makes it the best option in terms of treating malnutrition and would continue to expand the international market for the product which currently is estimated at US$40 billion (Foraminerera Market Research Website 2016)

•      It is estimated that about 20% of food protein worldwide is derived from legumes.

•      The highest consumption occurs in

•      the former Soviet Union

•      South America

•      Central America

•      Mexico

•      India

•      Turkey

•      Greece.

•      The dietary use of legumes is quantitatively in the following order:

•      Dry bean (Phaseolus vulgaris)

•      Dry pea (Pisum sativum)

•      Chickpea (Cicer arietinum)

•      Broad bean (Vicia faba)

•      Pigeon pea (Cajanus cajan)

•      Cowpea (Vigna unguiculata)

•      Lentil (Lens culinaris) (Agostini and Khan, 1986)

•      Peanut (Arachis hypogaea) and soyabean (Glycine max) are dominant sources of cooking oil and protein

•      They are also major food sources in some regions

•      The amino acid components of leguminous seed proteins commonly show deficiency in cysteine and methionine but when consumed in combination with cereal proteins, offer a complete nutritional balance.

•      Thus the legume complements the amino acid deficiencies in cereal grains.

•      Because of concerns over coronary heart disease and certain types of cancers, Nigerians have been admonished to reduce fat intake and increase intake of plant products as stated in Diet and Health (National Research Council, 1989)

•      Diets high in plant foods i.e. fruits, vegetables, legumes and whole grain cereals are associated with a lower occurrence of coronary heart disease and cancers of the lung, colon, oesophagus and stomach.

•      By using plant products (e.g. cereals and legumes) instead of animal products as sources of protein, one can also reduce the amount of saturated fatty acids and cholesterol in the diet

•      Foods highest in dietary fibre include unrefined grains (and breads made from them) legumes, vegetables, fruits, nuts and seeds

Pulses in Livestock field formulation

•      The importance of legumes in animal feed should not be overlooked.

•      Alfalfa (Medicago sativa), clover (Trifolium spp.), stylosanthes (Stylosanthes spp.), desmodium (Desmodium spp.) and other forages are grown extensively for livestock

•      They are either grazed or fed as hay or silage

•      Alfalfa silage furnishes not only roughage and high-quality protein but also a variety of vitamins, minerals and other nutrients

•      The anaerobic ensiling process supports a rapid fermentative acidification of the plant material, serving to preserve nutritional quality

•      Soyabean is used for the production of oil and the residual meal is an excellent and relatively inexpensive source of protein for livestock  especially monogastric animals

•      Although a small percentage of the meal is incorporated into human foods, most of it is used for feeding livestock and pets.

Seed	DM	CP	EE	NDF	ADF	ADL	NFE
Lima bean	65.8c	21.4d	2.4c	44.2c	21.7b	4.3d	17.3a
African yam bean	70.3a	25.2b	3.1bc	48.3ab	23.29	6.0b	11.7c
Pigeon Pea	68.7ab	21.6d	2.4c	48.3ab	19.2c	5.8c	13.2bc
Sword bean	63.6d	22.7c	3.6b	49.5a	20.6bc	6.2b	12.0c
Jack bean	69.4a	18.8e	3.3b	49.8a	22.3a	6.8a	11.4c
Lablab	67.6b	22.5c	3.6b	50.1a	22.5a	75.8c	10.6c
Bambara groundnut	67.5b	19.4e	2.8c	46.3b	19.8c	6.1b	14.8b
Soybean	67.3b	33.5a	10.1a	45.2c	16.4d	4.5d	15.6b
SEM	1.01	0.74	0.55	0.86	0.89	0.22	1.20

DM  =  Dry mater, CP  =  Crude protein,  CF  =  Crude Fibre,   EE  =  Eater extract,  NDF  =  Neutral Detergent fibre,  ADF  =n  Acid detergent,  ADL  =  Acid detergent lignin, NFE  =  Nitrogen free 

extract.   SEM  =  Standard error of the mean

Ref: Ajayi et al (2010)

Challenges of Productivity

•      Inspite of its ability to fix substantial amounts of its nitrogen nutrition, pulses have been found to give optimum yields if other factors are favourable

•      These include water supply, good agronomic practices, crop protection and appropriate time of planting

•      In I. A. R. & T., studies are on-going to identify the minor legumes that are going into extinction

•      The purpose is to increase the productivity, improve on the processing methods and study those factors capable of influencing the storage

•      The Product Development Programme of the institute is also working on the seeds in order to identify and understand their nutritional profile after processing for the purpose of further research to upgrade the value chain

•      It is very important to transform the pulses into industrial products or products with higher value added

•      The success in this regard depends on increasing the capacity of entrepreneurs in Nigeria to supply global, regional and local value chains with products matching specific standards, volume and packaging requirements

•      Research Institutes can then key into this and work on the products for further improvement

Economic Benefits

•      There must be positive net economic or other benefits to induce the farmer to plant pulses

•      Farmers are most likely to cultivate this crop if there is a reduction in the production costs and/or increased yields and also when it reduces or at least does not increase risk

•      Reduced production costs or higher yields of food and feed lead to increased production and ultimately to lower food prices

•      Thus the development and adoption or incorporation of the pulses in our farming systems can become a real engine for economic growth with society as a whole the beneficiary

•      The major problem in evaluating the economic benefits in the cultivation of the pulses is in assigning prices to inputs and outputs (Heinz and Welsch, 1991)

•      For the farmer, actual costs and income are critical

•       In developed countries, prices of products may be supported above world market levels as a means of protecting farmers’ income

•      On the contrary, in developing countries like Nigeria, prices may be controlled below world market levels to benefit urban residents and the industrial sector at the expense of farmers’ income

•      Given these problems, the only way to estimate the economic advantage of adopting Legume-Cereal Farming System is by analysis of cropping systems that use it as a source of nitrogen and protein for human consumption

•       If livestock are involved, then the analysis should be based on the entire farm operation

•      A number of factors determine the benefits from the cultivation of pulses to the producer including conditions on the farm, regulations at the local level, access to market and technology, community and local infrastructure and cultural values

Conclusions and Recommendations

•      Many years ago, the spiraling costs of energy and, as a consequence, the costs of nitrogen fertilisers, resulted in a new momentum for research in the area of farming systems research that incudes pulses as a component part

•      Research support for the farming systems has expanded and the knowledge base has increased

•      Soyabean production in Nigeria has increased

•      However, production of cowpea faces the challenges of pests and diseases especially in the southern ecologies of Nigeria

•      Research support has also increased in the field of plant protection

•      However, the minor legumes are going into extinction

•      Research work must continue on this important legumes

•      Technologies on this and other grain legumes must be validated and adopted

•      Agronomic practices that can lead to improved productivity must be extended to farmers

•      Using these set of legumes in Nigeria will further enrich the soils and increase plant protein intake 

•      We must upgrade the various value chains generated and create/develop markets for the products

•      The private sector must also get involved in this programme while the financial houses should make available single digit interest loans for investors in this field of agriculture

•      Aside from providing plant protein for the benefit of Nigerians, jobs will be created for the resource-poor women and youths leading to reduction in poverty.

•      Consequently, this will boost Nigerias’ economy