Iris Publishers - World Journal of Agriculture and Soil Science (WJASS)
Increase in The Use of Organic Fertilizers as Complements to Inorganic Fertilizers in Maintenance of Soil Fertility and Environmental Sustainability
Authored by Joseph Xorse Kugbe
Introduction
Soil
is taken for granted by most farmers, who often think of it as an inert support
for plants. In reality, it is a dynamic, living resource whose condition is
vital for food production and for the function of the ecosystem as a whole. The
fertility of soil can be considered in different ways, depending on land use.
In intensively managed agricultural and horticultural systems, and even in
forestry, soil fertility can be defined in terms of the value of products
produced relevant to inputs used (including economic aspects of nutrient
budgeting). Alternatively, the emphasis may be on quality or productivity.
Soil
fertility maintenance is a major concern in tropical Africa [1], particularly
with the rapid population increase, which has occurred in the past few decades.
In traditional farming systems, farmers use bush fallow, plant residues,
household refuse, animal manures and other organic nutrient sources to maintain
soil fertility, organic matter and general soil productivity. Although this
reliance on biological nutrient sources for soil fertility regeneration is
adequate for cropping systems with low cropping intensities, it becomes
unsustainable with more intensive cropping unless fertilizers are applied [2].
Thus,
the concept of soil fertility and the choice of fertility management is
specific to a given context. However, in all contexts, soil fertility depends
on physical, chemical and biological characteristics [3]. When soil fertility
is considered in terms of the highest practical level of productivity, the
focus is mostly on physical and chemical aspects of the soil. It is important
to note that some aspects of the biological component of soil fertility can be
overridden by addition of fertilizers, but this is not a simple phenomenon,
because increase in plant growth that is associated with addition of
fertilizers can increase other aspects of the biological activity in soil [4].
In a
sustainable agricultural or horticultural system, soil fertility can be
considered in terms of the amount of input relative to the amount of output
over a long period, using a budgeting approach [2]. This definition is
different from the one that defines fertility in relation to a maximum level of
productivity in the short-term or at a given point in time [5]. A definition
that focuses on shortterm productivity is based on the capacity of soil to
immediately provide plant nutrients [6]. When sustainability of the soil
resource is emphasized in the context of soil fertility, biological components
Citation: Joseph Xorse Kugbe, Wuni Mawiya, Alhassan Mohammed Hafiz, Charles
Maganoba. Increase in The Use of Organic Fertilizers as Complements to
Inorganic Fertilizers in Maintenance of Soil Fertility and Environmental
Sustainability. World J Agri & Soil Sci. 4(1): 2019. WJASS.MS.ID.000577.
DOI: 10.33552/WJASS.2019.04.000577. Page 2 of 4 may become more relevant
because of its long-term impact on productivity that has been variously
reported [7]. A change in focus from the highest practical level of
productivity to a lower, profitable and persistent level of production;
temporally depend on soil biological processes. In that sense, the physical,
chemical and biological components of soil are essential for sustained soil
productivity.
Environmental
Sustainability Essential for Today’s Soil Productivity
Sustainable
agriculture refers to a farming system that seeks to achieve maximum
productivity of crops and livestock that will satisfy human needs for food and
fibre whiles maintaining the integrity of the ecology. A productive soil needs
to be looked after. There is the need to make the most efficient use of all
non-renewable resources in the soil to sustain economic viability and enhance
the quality of life [8]. Sustainable agriculture adopts a holistic approach
with an ultimate goal of achieving continuity in health of the soil and the
people to which the system affects [9]. In that sense, all systems, processes
and interactions that eventually impact the soil health must be identified for
a given geographic location before long lasting impacts due to soil usage are
implemented. Often, and most especially across resource-poor zones like sub
Saharan Africa, knowledge of such location-specific soil interactions and
processes are limited in practice. The knowledge limitation hinders the efficient
and sustainable usage of soil resources for the benefit of the environment, and
for the production of food for the everincreasing human population [10].
Declining
Soil Fertility in the Guinea Savanna Zone of Africa Should be a Call for
Concern
Over
the years, enhancing and maintaining the fertility of soils across the Guinea
savanna zone of Africa have become very critical issues that need to be
addressed to meet the food security of these developing countries [1]. Soil
fertility has been impaired by continuous cropping; with low inputs of mineral
nutrients. This has been identified as a major threat, not only to food
production but also to ecosystem viability [11]. Generally, improving the
nutritional status of plants through the application of mineral fertilizers,
and the persistence maintenance of soil health and fertility has resulted into
the production of double the quantity of food produced in both developed and
developing countries since the beginning of the ‘Green Revolution’ [12]. Across
the Guinea Savanna zone, increases in cereal production in the past 40 years
are associated with corresponding increases in fertilizer consumption [13].
According
to Tillman [11] the doubling of food production during the past 40 years has
been associated with about 6.9-fold increases in N fertilization, 3.5-fold
increase in P fertilization and only 1.1-fold increase in cultivated land area.
Similar observations have been reported in Asia [14]. As human population
continues to increase however, this increase in fertilizer consumption is not
enough to sustain food security and would have to be increased to over 250 kg
ha-1 of NPK [12,14].
Nearly
all increases in projected food requirements in the next decades will be the
result of enhancements in yield per unit area and intensive use of agricultural
land [2]. To increase yield capacity of crop plants and to ensure global food
demand in 2020, fertilizer use should increase from 144 million tons in 1990 to
208 million tons in 2020 [13,15]. Possibly, this projected increase in
fertilizer consumption by 2020 will not be adequate to meet both food
production requirements and nutrient depletions that are due to nutrient
removal by harvesting crops from soils. This portion of the un-estimated
nutrient depletion should be of grave concern to soil scientists, as the value
of its estimate can help predict the temporal health of a given soil. Byrnes
and Bumb [16] estimate that by 2020, global fertilizer consumption should
increase up to 300 million tons to match required demands for food production
and nutrient removal from soils. In view of this estimates, there is the need
for countries in the Guinea savanna zone of Africa to develop and adopt
fertilizer accessible policies and take new measures to provide more support to
the resource-poor farmers regarding the supply of fertilizers.
Major
Challenges Facing Soil Fertility and Environmental Sustainability
Inadequate
use of fertilizers raises concerns due to its adverse effects on the
environment. The eutrophication of surface waters, pollution of drinking waters
and fertilizer-associated greenhouse gaseous emissions that causes global
warming are some environmental concerns [17-19]. There is a very close
relationship between application rates of N fertilizers and the emission of
nitrous oxide (N2O) [20]. Nitrous oxide is one of the most important greenhouse
gases that impacts the global climate [17]. About 0.5-1.5 of fertilizer N
applied is lost from soil as gaseous emissions [18,19]. Several management
strategies have been developed to control and minimize N losses. These include
use of N fertilizers with enzyme inhibitors like urease and nitrification
inhibitors, controlled-release N fertilizers, accurate timing and placement of
fertilizers, and soil and plant analysis to define rates of N application
[21-23].
In
these senses, nutrient use efficiency and improved soil management has become
an important challenge, particularly for N and P fertilizers [23]. When the
application of N fertilizers is not properly managed and is realized at
excessive levels, losses of N from agricultural lands can occur through the
leaching of NO3, volatilization of NH3 or emission of N oxides [17,20]. The
leaching and runoff of NO3 into ground water and surface waters is a major
environmental problem in developed countries, particularly in Europe [24]. It
is gaining increasing attention in fast growing economies like China and should
be avoided at all cost in Africa. Pollution of ground water with NO3 impairs
the quality of drinking water and causes various harmful effects on human
health [25]. Contamination of lakes and rivers with NO3 stimulates algal growth
and depletion of respiration-required oxygen, resulting in an increasing risk
of fish deaths on a large scale [25,26]. Adequate knowledge and use of both
organic and inorganic sources of fertilizers, in terms of time of application,
rate of application, method of application, and storage aid to reduce the
impact of fertilizer application and losses on the environment.
Combined
use of Organic and Inorganic Fertilizers Essential for Sustained Soil
Productivity
Several
studies have shown that the application of fertilizers, both from organic and
inorganic sources significantly improves the growth and yield of most crops
[27,28]. Thus, an integral use of both organic and inorganic fertilizer to
ensure adequate supply of plant nutrients and sustain maximum crop yield and
profitability has been advocated [4]. However, inorganic fertilizer is
expensive and may be largely unaffordable, hence not readily available to
resource-poor farmers across sub-Saharan Africa. Some findings show that the
intensive continuous application of inorganic fertilizers, solely, cannot
sustain the high yield of vegetable production [28]. On the other hand, organic
manure such as poultry droppings is comparatively available as a cheap source
of nutrients for sustainable crop production [15]. Besides the supply of
essential macro and micro nutrient elements to plants, organic fertilizers
improve soil physico-chemical conditions, enhance soil productivity, increase
the soil organic carbon content, soil flora and fauna, soil crumb structure and
the nutrient status of the soil towards attaining sustainably high yields [27].
Organic
inputs contain nutrients that are released at a rate determined in part by
their chemical characteristics or organic resource quality. For this reason,
organic inputs applied at realistic levels seldom release sufficient nutrients
for acceptable crop yield.
It has
been suggested that methods involved in the current agricultural production
should rather be geared towards strategies that are compatible with the
principles of sustainable intensification under the agricultural production
systems [14] and which are promising to the fulfilment of the needs of the
present and posterity. These are the ones that involve the mobilization and use
of all nutrient resources that are available to the farmer.
Combine
use of organic and mineral inputs has been advocated for smallholder farming in
the tropics because neither input is usually available in sufficient quantities
to maximize yields and also because both are needed in the long-term to sustain
soil fertility and crop production. An important question arises within the
context of integrated soil fertility management: Can organic resources be used
to rehabilitate less-responsive soils and make these responsive to fertilizer?
In Zimbabwe, applying farmyard manure to sandy soils at relatively high rates
for 3 years resulted in a clear response to fertilizer where there was no such
response before rehabilitation [29].
Conclusion
An integral use of both organic and
inorganic fertilizer to ensure adequate supply of plant nutrients and sustain
maximum crop yield and profitability is advocated. However, inorganic
fertilizer is expensive and may be largely unaffordable and not available to
the resource-poor farmers found mostly across sub sahara Africa. On the other
hand, organic manure, such as poultry droppings is readily available as a cheap
source of nutrients for sustainable crop production. Organic fertilizer
supplies the essential macro- and micro-nutrient elements to plants, as well as
improves soil physicochemical conditions for better crop growth and yield.
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