STRATEGIES TO REDUCE USE OF CHEMICAL FERTILIZERS AND MINIMIZE THE ENVIRONMENTAL IMPACT

Rather than increasing the rate of fertilizer input, it is incumbent upon soil/plant researchers and fertilizer manufacturers to identify and implement strategies that enhance the use efficiency of fertilizers and decrease losses and their transfer into the environment. Such strategies can be grouped into three categories (Figure 14.4), which depend on site-specific conditions including soil type, climate, farming system, and socioeconomic and cultural factors (Figure 14.5).

Strategies to reduce the input of chemical fertilizers and minimize the environmental footprint

FIGURE 14.4 Strategies to reduce the input of chemical fertilizers and minimize the environmental footprint.

Controls of fertilizer management options

FIGURE 14.5 Controls of fertilizer management options.

STRATEGIES TO REDUCE DEPENDENCE ON CHEMICAL FERTILIZERS

It is important that nutrients harvested in farm produce are replaced in one form or another. Soils of agroecosystems must not have a negative nutrient budget. A large quantity of plant nutrients (both macro and micro) are removed in grains (Table 14.3), stover/straw (Table 14.4), and also in animal and forest products. The amount of nutrients removed is more in a high-productivity system compared with that of a low-productivity system. Since the 1960s, harvested nutrients have mostly been replaced by chemical/synthetic fertilizers such as highly reactive nitrogenous formulations. Leakage of reactive N along with that of phosphorus (P) into aquatic ecosystems has created hypoxia, algal bloom, and numerous other environmental hazards. Similarly, transfer of reactive N into the atmosphere as nitrous oxide (NzO) has exacerbated global warming. Thus, the strategy is to identify alternatives to chemical/synthetic fertilizers for replacing the harvested nutrients.

Three determinants of alternate strategies of replacing the harvested nutrients include those that (1) enhance use efficiency, (2) improve agronomic performance, and (3) use innovative formulations of fertilizers (Figure 14.4). All three strategies depend on soil quality and functionality. Specifically, the use efficiency of inherent and imported plant nutrients is governed by a range of factors that impact soil quality and functionality, such as SOC concentration and stock in the rooting depth. Restoration of soil quality and functionality through increase in SOC concentration to the critical threshold level (-2%) can minimize losses by accelerated erosion, surface runoff and leaching, and volatilization. Further, nutrient use efficiency can also be enhanced by a balanced application of fertilizers along with that of biomass-C (i.e., CNPK rather than NPK). Yield-based and soil-test-based application of fertilizers is needed to develop a strategy for the balanced application of fertilizers. The use efficiency of nutrients also depends on microbial activity, especially that of mycorrhiza and

TABLE 14.3

Estimates of Macronutrients Harvested in Grains

Grain

Nutrients Harvested (Kg/Mg)

N

p2o5

k2o

Ca

Mg

S

Total

I

Cereals

Bailey

18.2

7.8

5.2

0.5

1.0

1.6

34.3

Corn

13.8

7.5

5.5

0.2

1.4

1.2

29.6

Oats

19.5

7.8

5.9

0.8

1.2

2.0

37.2

Rye

20.9

6.0

6.0

1.2

1.8

4.2

40.1

Sorghum

14.9

7.4

4.5

1.2

1.5

1.5

31.0

Wheat

20.8

10.4

6.3

0.2

2.5

1.3

41.5

Average

18.0

7.8

5.6

0.7

1.6

2.0

35.6

II

Pulses

Chickpea

60.7

9.2

39.2

8.7

18.7

7.3

143.8

Lentil

57.0

14.9

21.6

3.5

7.0

2.0

106.0

Pigeon pea

70.8

15.3

16.0

7.5

19.2

12.5

141.3

Soybeans

70.7

30.9

57.7

6.7

14.0

7.6

187.6

Average

64.8

17.6

33.6

6.6

14.7

7.4

144.7

Source: FAO, Current World Fertilizer Trends and Outlook to 2016, FAO, Rome, Italy, 2012; Bender, R., Nutrient Uptake and Partitioning in High-Yielding Corn, University of Illinois at Urbana- Champaign, Urbana, IL, 2012.

TABLE 14.4

Nutrient Contents in Crop Residues

Crop Residue

Grain: Straw Ratio

Concentration on Dry Mass Basis (%)

N

p2o5

k2o

I

Cereals Corn stover

1: 1.5

0.59

0.31

1.31

Millet stock

1:2.0

0.65

0.75

2.50

Rice straw

1: 1.5

0.58

0.23

1.66

Sorghum stalk

1:2.0

0.40

0.23

2.17

Wheat straw

1: 1.5

0.49

0.25

1.28

II

Legumes

Chickpea

1: 1.0

1.19

1.25

Pigeon pea

1:2.5

1.10

0.58

1.28

Pulses (average)

1: 1.0

1.60

0.15

2.0

III

Sugarcane

Trash

1:0.2

0.35

0.04

0.50

Source: FAO, Sources of Plant Nutrients and Soil Amendments, in Plant Nutrition for Food Security: A Guide for Integrated Nutrient Management, FAO, Rome, Italy, pp. 9I-235,2006.

rhizobium (see Section 14.5.2). Maintaining an optimal soil moisture regime by minimizing the drought-flood syndrome is also critical to achieving the dual goal of enhancing use efficiency of both water and nutrients (e.g., N, P).

Management of soil quality requires adoption of improved practices of soil, crop, animal, and tree management through a judicious integration of crops with trees, livestock, forages, and cover crops. The strategy is to strengthen cycling of C and plant nutrients so that these elements are neither transported out of the ecosystem (by erosion, leaching, or volatilization) nor released into the environment where they can be pollutants.

Then, there is a possibility of improved formulations of fertilizers so that use efficiency is maximized and losses into the environment (water, atmosphere) are minimized. Examples of some such formulations include nanofertilizer (Liu and Lai 2015, 2017; Liu et al. 2016) and slow-release formulations of highly soluble nitrogenous fertilizers (Staufenbeil 2018; Silva 2011).

14.3.1 Factors Affecting the Choice of Site-Specific Fertilizer Options

Indiscriminate use of chemical fertilizers can have severe environmental consequences in relation to eutrophication of w'ater and pollution of air, among others. The dependence of fertilizers should be minimized, and these must be used as amendments following scientific guidelines (e.g., soil test, crop requirement). Factors affecting the choice of site-specific strategies for the use of fertilizers include biophysical, socioeconomic, cultural, and others related to the human dimensions. Important among biophysical parameters are soil type, climate, farming/cropping system, terrain, season, and weather patterns during the season. Pertinent issues of the human dimensions, especially in developing countries with predominantly small landholders, are infrastructure (e.g., roads, access to market, credit availability), institutional support (e.g., extension services, IT communication), and education and technical skills of the farming community (Figure 14.5). These factors vary among ecoregions and biome and have strong implications for the overall goal of judicious management of the environment and of human resources (Figure 14.5).

 
Source
< Prev   CONTENTS   Source   Next >