**Use of Organic Fertilizers to Enhance Soil Fertility, Plant Growth, and Yield in a Tropical Environment**

Amjad A. Ahmad, Theodore J.K. Radovich, Hue V. Nguyen, Jensen Uyeda, Alton Arakaki, Jeana Cadby, Robert Paull, Jari Sugano and Glenn Teves

Additional information is available at the end of the chapter

http://dx.doi.org/ 10.5772/62529

#### **Abstract**

[137] Cavichiolo S.B.V., Dedecek R.A., Gava J.L. Modificações nos atributos físicos de solos submetidos a dois sistemas de preparo em rebrota de *Eucalyptussaligna.* Revista Árvore.

[138] Reichert J.M., Suzuki L.E.A.S., Reinert D.J., Horn R., Hakansson I. Reference bulk density and critical degree‐of‐compactness for no‐till crop production in subtropical

[139] Epron D., Nouvellon Y., Deleporte P., Ifo S., Kazotti G., M'bou A.T., et al. Soil carbon balance in a clonal *Eucalyptus* plantation in Congo; effects of logging on carbon inputs

[140] Hernández J., DelPino A., Salvo L., Arrarte G. Nutrient export and harvest residue decomposition patterns of *Eucalyptus dunnii m*aiden plantation in temperature climate

[141] Jones H.E., Madeira M., Herraez L., Dighton J., Fabião A., González‐Rio F., et al. The effect of organic‐matter management on the productivity of *Eucalyptus globules* stands in Spain and Portugal: tree growth and harvest residue decomposition in relation to

[142] Zilda J.D., Bouillet J.P., Laclau J.P., Ranger J. The effects of slash management on nutrient cycling and tree growth in *Eucalyptus* plantations in the Congo. Forest Ecology

[143] Shammas K., O'Connell A.M., Grove T.S., Mcmurtrie R., Damon P., Rance S.J. Contri‐ bution of decomposition harvest residues to nutrient cycling in a second rotation *Eucalyptus globules* plantation in south‐western Australia. Biology and Fertility of Soils.

highly weathered soils. Soil and Tillage Research. 2009;242–254.

and soil CO2 efflux. Global Change Biology. 2006;12:1021–1031.

of Uruguay. Forest Ecology and Management. 2009;258:92–99.

and Management. 2002;171:209–221.

2003;38:228–235.

site and treatment. Forest Ecology and Management. 1999;122:73–86.

2005;29:571–577.

84 Organic Fertilizers - From Basic Concepts to Applied Outcomes

Soils rarely have sufficient nutrient for crops to reach their potential yield. Applying organic fertilizers without prior knowledge of their properties may cause yield decline under low application or pollute the environment with excessive application. Under‐ standing the nutrient variability and release pattern of organic fertilizers is crucial to supply plants with sufficient nutrients to achieve optimum productivity, while also rebuilding soil fertility and ensuring protection of environmental and natural resour‐ ces. This chapter presents the authors' experiences with different organic amend‐ ments under Hawaii's tropical conditions, rather than an intensive literature review. For meat and bone meal by‐products (tankage), batch‐to‐batch variability, nutrient content/ release pattern and quality, and plant growth response to the liquid fertilizer pro‐ duced from tankage were evaluated. For animal livestock, dairy manure (DM) and chicken manure (CM) quality, changes in soil properties, and crop biomass produc‐ tion and root distributions were evaluated. For seaweed, an established bio‐security protocol, nutrient, especially potassium (K) variability, and plant growth and yield response were evaluated in different tropical soils.

**Keywords:** organic fertilizers, tropical soils, nutrient variability, mineralization, plant growth, yield

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

### **1. Introduction**

Sustainable and organic agriculture practices apply management ideals that include a diverse assembly of farming methods, usually with a reduced reliance on purchased inputs [1], this is especially for new farmers with limited resources [2]. As commercial fertilizer/shipping costs increase, a wide range of food producers in the Hawaii and the Pacific region have realized the need for locally available fertilizers from organic sources to improve soil fertility, crop health, and productivity. In addition to concerns surrounding availability of affordable soil amend‐ ments, interest in sustainability and organically produced crops has risen among American consumers in the past few decades. Increased tourism has further amplified the need for fresh local fruits and vegetables, especially "locally grown" labeled goods. Shifting from conven‐ tional farming to organic farming has many benefits to the human's well‐being, protecting the environment (soil, water, and air), rebuilding soil fertility through improving its physical, chemical, and biological characteristics, and improving the quality of produced crops [3]. However,producingcropsorganicallymaycomewithhigherproductioncosts (i.e.,loweryield and higher labor costs). Recycling, composting, and using local inputs may decrease the production cost [4]. In general, soils rarely have sufficient nutrients available for crops to reach their potential yield. Therefore, farmers tend to apply soil amendments (synthetic or organic amendments) that are rich in nutrient, i.e., N, P, and K to enhance soil fertility and increase crop productivity [5]. However, most growers apply fertilizers based on the general recommenda‐ tions for each crop [6], without prior knowledge of the soil fertility status and nutrient miner‐ alization and release pattern from the fertilizers [7]. In addition, Hawaii farmers face the continuous challengeofdecliningsoilorganicmatter(SOM) andfertility[8]due totheoptimum environmental condition (e.g., temperature and rainfall) for SOM decomposition [9]. These lossesaremorecriticalwiththeuseoforganicamendments,wherenutrientshavetobeconverted from organic to inorganic forms in order to be available for plant uptake [10]. Also, rebuilding/ restoring soil fertility and improving the physical, chemical, and biological function of soils are critical to support optimal plant growth, yield, and quality [11]. Sustainable health of the soil relies on carbon‐rich amendments that will feed the biological processes that are the core foundation of a healthy soil [12]. Short‐term needs must also be met with fertilizers that rapidly become available to plants, so that nutrients are available in synchrony with plant needs [13]. In Hawaii, there are many locally available resources to meet both long‐ and short‐term crop nutrient and soil function needs when used properly [14]. Improving farmers' knowledge and their capacity to determine the quality of different fertilizers and soil and crop's needs are essential elements in organic agriculture [15]. This chapter focuses on the authors' experien‐ ces with certain organic fertilizers that are available in Hawaii rather than being an extensive review of them.

#### **2. Meat and bone meal by‐products (tankage)**

Tankage is the solid by‐product of animal waste rendering (**Figure 1**). The nutrient content of tankage varies with feedstock and storage time, but the product available in Hawaii has been fairly consistent on average 9.5, 2.5, and 0.75% of N, P, and K, respectively, With a Carbon/ Nitrogen (C/N) ratio of 5:1 [16, 17]. The Hawaii material is derived from fish scraps (∼50%), waste meat, carcasses, and other mixed materials (∼45%) and offal (∼5%). The current and only running plant in Hawaii is producing about 25 tons/month. Often called meat and bone meal, tankage is a valuable agricultural input used as fertilizer in Hawaii for at least 20 years [18, 19]. The material is National Organic Program (NOP) compliant and listed as an approved generic material by OMRI. The primary agricultural use of tankage is as a supplemental N source [20], especially for, but not limited to, certified organic growers. Nitrogen (N) miner‐ alization rates for tankage have always been assumed to be high given its low C/N ratio and high N content, but actual mineralization rates in Hawaii soils have not been readily available. Other gaps in our knowledge of this material include batch‐to‐batch variability in the material and N loss during storage.

**Figure 1.** Meat and bone meal by‐products (tankage).

**1. Introduction**

86 Organic Fertilizers - From Basic Concepts to Applied Outcomes

review of them.

**2. Meat and bone meal by‐products (tankage)**

Tankage is the solid by‐product of animal waste rendering (**Figure 1**). The nutrient content of tankage varies with feedstock and storage time, but the product available in Hawaii has been

Sustainable and organic agriculture practices apply management ideals that include a diverse assembly of farming methods, usually with a reduced reliance on purchased inputs [1], this is especially for new farmers with limited resources [2]. As commercial fertilizer/shipping costs increase, a wide range of food producers in the Hawaii and the Pacific region have realized the need for locally available fertilizers from organic sources to improve soil fertility, crop health, and productivity. In addition to concerns surrounding availability of affordable soil amend‐ ments, interest in sustainability and organically produced crops has risen among American consumers in the past few decades. Increased tourism has further amplified the need for fresh local fruits and vegetables, especially "locally grown" labeled goods. Shifting from conven‐ tional farming to organic farming has many benefits to the human's well‐being, protecting the environment (soil, water, and air), rebuilding soil fertility through improving its physical, chemical, and biological characteristics, and improving the quality of produced crops [3]. However,producingcropsorganicallymaycomewithhigherproductioncosts (i.e.,loweryield and higher labor costs). Recycling, composting, and using local inputs may decrease the production cost [4]. In general, soils rarely have sufficient nutrients available for crops to reach their potential yield. Therefore, farmers tend to apply soil amendments (synthetic or organic amendments) that are rich in nutrient, i.e., N, P, and K to enhance soil fertility and increase crop productivity [5]. However, most growers apply fertilizers based on the general recommenda‐ tions for each crop [6], without prior knowledge of the soil fertility status and nutrient miner‐ alization and release pattern from the fertilizers [7]. In addition, Hawaii farmers face the continuous challengeofdecliningsoilorganicmatter(SOM) andfertility[8]due totheoptimum environmental condition (e.g., temperature and rainfall) for SOM decomposition [9]. These lossesaremorecriticalwiththeuseoforganicamendments,wherenutrientshavetobeconverted from organic to inorganic forms in order to be available for plant uptake [10]. Also, rebuilding/ restoring soil fertility and improving the physical, chemical, and biological function of soils are critical to support optimal plant growth, yield, and quality [11]. Sustainable health of the soil relies on carbon‐rich amendments that will feed the biological processes that are the core foundation of a healthy soil [12]. Short‐term needs must also be met with fertilizers that rapidly become available to plants, so that nutrients are available in synchrony with plant needs [13]. In Hawaii, there are many locally available resources to meet both long‐ and short‐term crop nutrient and soil function needs when used properly [14]. Improving farmers' knowledge and their capacity to determine the quality of different fertilizers and soil and crop's needs are essential elements in organic agriculture [15]. This chapter focuses on the authors' experien‐ ces with certain organic fertilizers that are available in Hawaii rather than being an extensive

#### **2.1. Nutrient content and nitrogen release pattern**

#### *2.1.1. Nutrient content variability among tankage batches*

Batch‐to‐batch evaluation was carried out for 2 years by collecting tankage samples (every 3 months) from Island Commodities Co., on Oahu. Initial subsamples were submitted to the University of Hawaii's Agricultural Diagnostic Services Center (ADSC) for total nutrient content analysis. The results showed that tankage can provide fairly good amount of the macro‐ and micro‐nutrient, except potassium (K), which was fairly low. N content in tankage initial samples varied between 8.7% and 12.1% with an average of 9.8%, and C/N ratio varied between 3.5 and 5.3:1 with an average of 4.7:1 (**Table 1**). Periodical analysis of N content in the stored initial tankage samples under lab condition showed a significant continuous decline in N content from 10% to 30% of the initial N (date not presented). N volatilization in the form of ammonia (NH3) is a major source of N loss to the atmosphere. Soil acidification is caused by an increase in H+ resulting from the deposition of the NH3 into the soil. Under field/farm condition (higher temperature, humidity, rainfall, etc.), N loss is expected to be higher and faster because climate is the major factor leading to increased N loss [21].


\* Each value is a mean of three replicates.

**Table 1.** Tankage macro‐ and micro‐nutrient content (μg/g), C/N ratio, standard deviation, and CV of samples collected over a 2‐year period.

#### *2.1.2. Nitrogen release pattern*

To determine the N release pattern from tankage, a leachate column incubation experiment was conducted using tankage applied at four application rates (0, 100, 200, and 400 kg N/ha) with two soils [Wahiawa series (Oxisol) and Waialua series (Mollisol)] with three replicates for each application rate. A total of 24 PVC leachate columns (30 cm long and 10 cm diameter) were used. The columns were set up from top to bottom with 10 cm soil and tankage mixed layer, 15 cm soil layer, 2 cm gravel layer, and plastic fine mesh to prevent soil passing through. Incubation started with adding half‐pore volume of deionized water for each column. At each collection time (weekly), half‐pore volume of deionized water was added, and leachate subsamples were collected with glass beaker up to 3 months. Leachate subsamples were analyzed for nitrate (NO3‐N) and ammonium (NH4‐N) using a Vernier meter and electrodes. Results showed that NO3‐N concentration in the leachate solutions followed the application rate (**Figure 2A** and **2B**), and NH4‐N concentration in the leachate samples was very negligible (0.1–2.7 ppm). The mineralization rate in a 3‐month period was between 50% and 75%. Under field conditions, actual mineralization is expected to be at or above the higher end of this range. The N release pattern under the two soils was the same. However, the NO3‐N values were higher under the Oxisol soil (Wahiawa series), which might be related to the fertility level and structural differences between the two soil types [22].

between 3.5 and 5.3:1 with an average of 4.7:1 (**Table 1**). Periodical analysis of N content in the stored initial tankage samples under lab condition showed a significant continuous decline in N content from 10% to 30% of the initial N (date not presented). N volatilization in the form of ammonia (NH3) is a major source of N loss to the atmosphere. Soil acidification is caused by an increase in H+ resulting from the deposition of the NH3 into the soil. Under field/farm condition (higher temperature, humidity, rainfall, etc.), N loss is expected to be higher and

May 2012 10.6 45.57 4.3 3.21 0.92 6.06 0.18 0.78 1069 12 97 4 5 Aug 2012 10.3 45.50 4.4 3.54 0.83 6.22 0.17 0.77 788 9 96 4 2 Nov 2012 12.1 42.26 3.5 3.22 1.07 5.81 0.19 0.92 662 12 106 4 4 Feb 2013 9.8 47.10 4.7 3.50 0.73 6.18 0.17 0.72 730 8 91 5 3 May 2013 8.7 45.93 5.1 3.16 0.74 5.70 0.17 0.65 745 10 85 1 3 Aug 2013 8.9 46.81 5.3 3.23 0.83 5.88 0.18 0.83 728 8 91 3 4 Nov 2013 8.8 46.13 5.3 3.07 0.81 5.55 0.17 0.72 738 10 85 1 3 Feb 2014 9.3 45.81 4.9 3.09 0.81 5.43 0.17 0.69 667 9 75 2 3 May 2014 9.4 45.93 4.9 3.48 0.85 6.05 0.17 0.72 725 9 88 4 3 **Mean 9.8 45.6 4.7 3.27 0.84 5.87 0.17 0.75 761 9.7 90 3.1 3.3 SD 1.09 1.38 0.58 0.18 0.10 0.28 0.01 0.08 121 1.5 8.8 1.5 0.8 CV 0.11 0.03 0.12 0.06 0.12 0.05 0.04 0.11 0.16 0.16 0.1 0.5 0.2**

**Table 1.** Tankage macro‐ and micro‐nutrient content (μg/g), C/N ratio, standard deviation, and CV of samples

To determine the N release pattern from tankage, a leachate column incubation experiment was conducted using tankage applied at four application rates (0, 100, 200, and 400 kg N/ha) with two soils [Wahiawa series (Oxisol) and Waialua series (Mollisol)] with three replicates for each application rate. A total of 24 PVC leachate columns (30 cm long and 10 cm diameter) were used. The columns were set up from top to bottom with 10 cm soil and tankage mixed layer, 15 cm soil layer, 2 cm gravel layer, and plastic fine mesh to prevent soil passing through. Incubation started with adding half‐pore volume of deionized water for each column. At each collection time (weekly), half‐pore volume of deionized water was added, and leachate subsamples were collected with glass beaker up to 3 months. Leachate subsamples were analyzed for nitrate (NO3‐N) and ammonium (NH4‐N) using a Vernier meter and electrodes. Results showed that NO3‐N concentration in the leachate solutions followed the application

**N C C/N P K Ca Mg Na Fe Mn Zn Cu B**

faster because climate is the major factor leading to increased N loss [21].

88 Organic Fertilizers - From Basic Concepts to Applied Outcomes

**Collection date % μg/g**

\* Each value is a mean of three replicates.

collected over a 2‐year period.

*2.1.2. Nitrogen release pattern*

**Figure 2.** NO3‐N (ppm) release in a leachate column study from tankage applied at 0, 100, 200, and 400 lbs N/acre over 90‐day periods under Mollisol (A) and Oxisol (B) soils.

#### **2.2. Liquid fertilizer from tankage for fertigation purposes**

Fertigation (fertilizer + irrigation) is a practice when both water and nutrient are supplied together through drip irrigation [23]. The practice is very beneficial for long‐term crops, to meet the demand of crops for nutrient, integrated with the use of mulching, and to reduce nutrient losses [24]. Through a Western Sustainable Agriculture Research and Education grant, producing liquid fertilizer with high‐N content from tankage was carried out at the University of Hawaii at Manoa (**Figure 3**).

**Figure 3.** Flask contains 1 g tankage and 50 ml water. Each treatment was replicated three times.

#### *2.2.1. Factors studied and final recipe*


On the basis of the results from the previous study (**Figure 4**), different factors in various combinations were evaluated for the N release from tankage. Based on these results, a suggested recipe was developed for greenhouse and on‐farm trials:


Use of Organic Fertilizers to Enhance Soil Fertility, Plant Growth, and Yield in a Tropical Environment http://dx.doi.org/ 10.5772/62529 91

**Figure 4.** Nitrate release (ppm) from tankage under the effect of time (hours); temperature (°C); open or covered condi‐ tions, and chemical and biological agents. Bars with different letters, within each factor, are significantly different un‐ der 5% probability.

We found that the use of fresh tankage and vermicompost resulted in a higher N concentration in the liquid fertilizer. In addition, the use of thick cotton un‐dyed bag to mix the tankage and vermicompost prior to brewing helped significantly reduce the need to strain the liquid fertilizer before fertigation.

#### *2.2.2. On‐farm and field trials*

**2.2. Liquid fertilizer from tankage for fertigation purposes**

90 Organic Fertilizers - From Basic Concepts to Applied Outcomes

**Figure 3.** Flask contains 1 g tankage and 50 ml water. Each treatment was replicated three times.

of Hawaii at Manoa (**Figure 3**).

*2.2.1. Factors studied and final recipe*

**Treatment factor Level**

Incubation time 0, 4, 8, 24, and 48 hours

Incubation temperature 24°C and 35°C (75°F and 95°F) Cover/lid Covered and open/uncovered

Inoculants/accelerators Baking soda, soil, sugar, and vermicompost

suggested recipe was developed for greenhouse and on‐farm trials:

**•** Add 1 kg (2.2 lbs) of tankage into 60 l (∼15 gallon) water.

**•** Add about 40 g (1.5 oz) of vermicompost.

**•** Strain and apply with drip irrigation (fertigation).

**•** Air (brew) for 12–24 hours.

On the basis of the results from the previous study (**Figure 4**), different factors in various combinations were evaluated for the N release from tankage. Based on these results, a

Fertigation (fertilizer + irrigation) is a practice when both water and nutrient are supplied together through drip irrigation [23]. The practice is very beneficial for long‐term crops, to meet the demand of crops for nutrient, integrated with the use of mulching, and to reduce nutrient losses [24]. Through a Western Sustainable Agriculture Research and Education grant, producing liquid fertilizer with high‐N content from tankage was carried out at the University

> The above recipe was provided to a local farmer in Hawaii. The farmer used the recipe to grow watermelon on a 1‐acre field with a Oxisol soil (Molokai series). The liquid fertilizer recipe was

applied weekly till 2 weeks prior to harvest. The experiment was not fully replicated, but the results were consistent throughout the field. Randomly selected watermelon subsamples were taken, and the average weight and total soluble solid (TSS) contents were taken (**Table 2**). The TSS values were within the excellent range (10.2–13.0) for watermelon [25]. Also, the average weight and watermelon flesh color were representative of the overall crop quality. The yield and high TSS value suggested that the liquid fertilizer provided good amount of nutrient to the watermelon to grow well and accumulate the high‐sugar content. As the on‐farm field trial was not fully replicated, we conducted a field trial on Oahu Island at Poamoho Research Station on an Oxisol (Wahiawa series) soil. The objectives of the trial were to evaluate the effect of two liquid fertilizers (organic and synthetic) on the yield of different vegetable crops. The experi‐ ment was conducted on a 21 × 18 m area for three consecutive harvests of lettuce (*Lactuca sativa*), pak‐choi (*Brassica rapa*, Chinensis Group), and daikon (*Raphanus sativus*) in a random‐ ized complete block design (RCBD) with three replicates. Lettuce and pak‐choi seedlings were transplanted after 2 weeks of seeding into trays in the greenhouse. Daikon was directly seeded into the field. The liquid fertilizers (tankage‐ and synthetic‐based) were injected into the drip irrigation weekly. To ensure a uniform distribution of the liquid fertilizer, the irrigation water was applied till the drip pipes were completely filled, and then the liquid fertilizers were injected. Lettuce, pak‐choi, and daikon were harvested at 4, 5, and 9 weeks, respectively. Leaf chlorophyll content of five randomly selected plants from each replicate was measured weekly using SPAD Minolta 502 m. At harvest, five random plants from each replicate were measured for fresh weight and dry weight (samples were dried at 70°C for 72 hours). The analysis of variance results were consistent throughout the three consecutive harvests, where the results showed a significant effect of the liquid fertilizer treatments on the fresh and dry weights of the harvested crops and leaf chlorophyll content. The fresh and dry weight means from tankage‐based liquid fertilizer treatments were significantly higher (*P* < 0.01) than the syn‐ thetic‐based liquid fertilizer (**Figure 5A** and **5B**). Also, the leaf chlorophyll content values were significantly higher under tankage‐based liquid fertilizer than synthetic‐based liquid fertilizer (**Figure 6**).


Data were taken from different locations in each watermelon fruit.

Data were collected by Alton Arakaki, an Extension Agent on Molokai Island.

**Table 2.** Average weight (lbs) and TSS of three watermelon fruit harvested randomly from the Molokai on‐farm trial.

Use of Organic Fertilizers to Enhance Soil Fertility, Plant Growth, and Yield in a Tropical Environment http://dx.doi.org/ 10.5772/62529 93

applied weekly till 2 weeks prior to harvest. The experiment was not fully replicated, but the results were consistent throughout the field. Randomly selected watermelon subsamples were taken, and the average weight and total soluble solid (TSS) contents were taken (**Table 2**). The TSS values were within the excellent range (10.2–13.0) for watermelon [25]. Also, the average weight and watermelon flesh color were representative of the overall crop quality. The yield and high TSS value suggested that the liquid fertilizer provided good amount of nutrient to the watermelon to grow well and accumulate the high‐sugar content. As the on‐farm field trial was not fully replicated, we conducted a field trial on Oahu Island at Poamoho Research Station on an Oxisol (Wahiawa series) soil. The objectives of the trial were to evaluate the effect of two liquid fertilizers (organic and synthetic) on the yield of different vegetable crops. The experi‐ ment was conducted on a 21 × 18 m area for three consecutive harvests of lettuce (*Lactuca sativa*), pak‐choi (*Brassica rapa*, Chinensis Group), and daikon (*Raphanus sativus*) in a random‐ ized complete block design (RCBD) with three replicates. Lettuce and pak‐choi seedlings were transplanted after 2 weeks of seeding into trays in the greenhouse. Daikon was directly seeded into the field. The liquid fertilizers (tankage‐ and synthetic‐based) were injected into the drip irrigation weekly. To ensure a uniform distribution of the liquid fertilizer, the irrigation water was applied till the drip pipes were completely filled, and then the liquid fertilizers were injected. Lettuce, pak‐choi, and daikon were harvested at 4, 5, and 9 weeks, respectively. Leaf chlorophyll content of five randomly selected plants from each replicate was measured weekly using SPAD Minolta 502 m. At harvest, five random plants from each replicate were measured for fresh weight and dry weight (samples were dried at 70°C for 72 hours). The analysis of variance results were consistent throughout the three consecutive harvests, where the results showed a significant effect of the liquid fertilizer treatments on the fresh and dry weights of the harvested crops and leaf chlorophyll content. The fresh and dry weight means from tankage‐based liquid fertilizer treatments were significantly higher (*P* < 0.01) than the syn‐ thetic‐based liquid fertilizer (**Figure 5A** and **5B**). Also, the leaf chlorophyll content values were significantly higher under tankage‐based liquid fertilizer than synthetic‐based liquid fertilizer

(**Figure 6**).

**Melon Weight (lbs) TSS/sample location BRIX mean 1 2 3 4 5**

Data were taken from different locations in each watermelon fruit.

Data were collected by Alton Arakaki, an Extension Agent on Molokai Island.

**Table 2.** Average weight (lbs) and TSS of three watermelon fruit harvested randomly from the Molokai on‐farm trial.

1 24 10.2 12.0 12.2 12.3 12.1 **11.8** 2 19 10.8 12.0 12.2 11.8 10.8 **11.5** 3 18 11.2 13.0 13.0 13.0 12.0 **12.4**

92 Organic Fertilizers - From Basic Concepts to Applied Outcomes

**Mean 20.3 10.7 12.3 12.5 12.4 11.6**

**Figure 5.** Fresh weight (A) and dry weight (B) for lettuce, pak‐choi, and daikon under organic (tankage) and synthetic (30–10–10) liquid fertilizer application.

**Figure 6.** Weekly changes in leaf chlorophyll content under liquid‐tankage and liquid‐synthetic treatments for lettuce, pak‐choi, and daikon crops, respectively, using Minolta Chlorophyll Meter.

#### **3. Livestock manure**

Using livestock on small‐scale farms is beneficial for supplying small family needs for milk, eggs, meat, and other goods/products. Also, it can be a good source of organic fertilizer [26]. For example, on average, a 1000‐pound cow may produce about 15 tons of manure annually. This 15‐ton may contain about: 200 lbs of N, 190 lbs of phosphorus (P2O5), and 250 lbs of potassium (K2O). Also, dairy manure (DM) contains the essential micro‐nutrients [calcium (Ca), magnesium, sulfur, manganese, copper, zinc, chlorine, boron, iron, and molybdenum] [27]. Another example is chicken manure (CM), which contains all of the essential nutrients needed for healthy plant growth [28]. These include N, phosphorous, K, Ca, magnesium, sulfur, manganese, copper, zinc, chlorine, boron, iron, and molybdenum. Nutrient content and percentages vary based on the feed, supplement, medications, and water consumed by the animals. CM is known to provide a good portion, if not all of the nutrients required by plants [29]. Livestock manure is commonly applied in irrigated agriculture to improve soil fertility and crop yields [30, 31] and to improve the soil biology [32]. Soil physical properties, for example, bulk density and total soil porosity may change with agricultural management practices [33]. Manure amendments increase SOM, which may decrease soil bulk density and increase porosity of the amended soil [34]. Animal manures need to be well composted before application to benefit both soil and plants [6]. However, NO3‐N leaching can be a problem in organic and conventional farming. Under aerobic soil condition and with heavy application of manure, organically bound N is rapidly converted biologically into NO3‐N and that is highly leachable in soils or runoff and can lead to environmental and health issues. In a field study, we used CM applied to a Mollisol soil (Waialua series) under sweet corn crop, at a high‐ application rate (30 ton/ha); the NO3‐N concentration in soil water leached below the root zone

**Figure 7.** Nitrate (ppm) below the root zone of sweet corn under different application rates (ton/ha) of chicken manure (CM) applied to Mollisol soil (Waialua series) in Hawaii.

of corn was very high and could lead to potential groundwater contamination (**Figure 7**). Moderate applications (7.5 and 15 ton/ha) and timing of manure application to meet plant needs may reduce the environmental pollution risks [35].

#### **3.1. Livestock manure effects on soil physical properties and root distribution**

#### *3.1.1. Soil physical properties*

**3. Livestock manure**

94 Organic Fertilizers - From Basic Concepts to Applied Outcomes

Using livestock on small‐scale farms is beneficial for supplying small family needs for milk, eggs, meat, and other goods/products. Also, it can be a good source of organic fertilizer [26]. For example, on average, a 1000‐pound cow may produce about 15 tons of manure annually. This 15‐ton may contain about: 200 lbs of N, 190 lbs of phosphorus (P2O5), and 250 lbs of potassium (K2O). Also, dairy manure (DM) contains the essential micro‐nutrients [calcium (Ca), magnesium, sulfur, manganese, copper, zinc, chlorine, boron, iron, and molybdenum] [27]. Another example is chicken manure (CM), which contains all of the essential nutrients needed for healthy plant growth [28]. These include N, phosphorous, K, Ca, magnesium, sulfur, manganese, copper, zinc, chlorine, boron, iron, and molybdenum. Nutrient content and percentages vary based on the feed, supplement, medications, and water consumed by the animals. CM is known to provide a good portion, if not all of the nutrients required by plants [29]. Livestock manure is commonly applied in irrigated agriculture to improve soil fertility and crop yields [30, 31] and to improve the soil biology [32]. Soil physical properties, for example, bulk density and total soil porosity may change with agricultural management practices [33]. Manure amendments increase SOM, which may decrease soil bulk density and increase porosity of the amended soil [34]. Animal manures need to be well composted before application to benefit both soil and plants [6]. However, NO3‐N leaching can be a problem in organic and conventional farming. Under aerobic soil condition and with heavy application of manure, organically bound N is rapidly converted biologically into NO3‐N and that is highly leachable in soils or runoff and can lead to environmental and health issues. In a field study, we used CM applied to a Mollisol soil (Waialua series) under sweet corn crop, at a high‐ application rate (30 ton/ha); the NO3‐N concentration in soil water leached below the root zone

**Figure 7.** Nitrate (ppm) below the root zone of sweet corn under different application rates (ton/ha) of chicken manure

(CM) applied to Mollisol soil (Waialua series) in Hawaii.

Most commonly available animal manures in Hawaii are CM and DM. Macro‐ and micro‐ nutrient content and C/N ratio for the CM and DM used for field trials on Oahu, Hawaii, are presented in **Table 3**. Under the Wahiawa series soil using CM and DM applied at four application rates (0, 165, 335, and 670 kg N/ha), soil bulk density (*ρ*b) and total porosity (*θ*<sup>t</sup> ) were measured using soil core samples. Soil bulk density significantly decreased with increased manure type (*P* < 0.01) and application rate (*P* < 0.05). Soil bulk density values for manure type and application rate were significantly different from the control treatment (**Figure 8A**). The soil bulk density was lowest under CM/high‐application rate (670 kg N/ha) as compared to all other treatments. Bulk density decreased by 4%, 8%, and 9% for the low, medium, and high application rates, respectively, compared to control. Total soil porosity significantly (*P* < 0.05) increased with manure type and application rate. Soil porosity increased by 3%, 5%, and 10% for low, medium, and high application rates, respectively, compared to control. However, there was no significant difference between manure type and application rate (**Figure 8B**). The changes in soil physical properties could be related to the increase in SOM depending upon the animal manure type and application rate, and as Ref. [36] suggested the organic matter (animal manure) application can have different effects on soil properties by adding "less dense" material or by changing soil aggregate.


**Table 3.** Macro‐ and micro‐nutrient and C/N ratio in chicken and dairy manure used in the field trials on Oahu, Hawaii.

Changes in soil bulk density and total porosity under chicken manure (CM) and dairy manure (DM) applied at 0 (Con), 165 (L), 335 (M), and 670 (H) kg N/ha. Means followed with different letters are significantly different at 5% probability based on Duncan's multiple test.

**Figure 8.** Changes in soil bulk density and total porosity under chicken manure (CM) and dairy manure (DM) applied at 0 (Con), 165 (L), 335 (M), and 670 (H) kg N/ha. Means followed with different letters are significantly different at 5% probability based on Duncan's multiple test.

#### *3.1.2. Sweet corn root distribution*

In the same field study above, sweet corn (*Zea mays* L. subsp. *mays*) percent roots at three depths (0–15, 15–30, and 30–45 cm depth) were evaluated for same animal manure types and appli‐ cation rates. The study included collecting soil cores from three locations, total of nine soil cores/plant, around the plant stem of five randomly selected plants in plots that measured 2 × 9 m each. The roots were collected from each soil core manually. As no visible roots were found in the cores collected from 30 to 45 cm depth, the results were considered for the top two depths (0–15 and 15–30 cm) only. The root percentage at the 0–15 cm depth under the CM and DM treatments was significantly (*P* < 0.05) higher than the control treatment (**Figure 9A**). However, the root percentage at the 15–30 cm depth showed the opposite pattern and root percentage under the CM and DM treatments was significantly (*P* < 0.05) lower than the control treatment (**Figure 10B**). The animal manure application rate increased significantly (*P* < 0.05) the root percentage at the top (0–15 cm depth) layer as compared to control treatment. The highest root percentage was for 670 kg N/ha (high) application rate, and the lowest mean was the control treatment. However, the reversed results were obtained from the lower (15–30 cm depth) layer, where the highest root percentage was the control treatment (**Figure 9B**). The increase in root biomass at 15–30 cm depth under the control treatment might be related to the expansion of roots' seeking water and nutrients beyond the top 15 cm (plowing layer) of soil as compared to the availability of nutrient (animal manure) within the top 15 cm soil layer under CM and DM treatments [37] or due to changes in soil bulk density as previously mentioned by Celik et al. [38].

**Figure 8.** Changes in soil bulk density and total porosity under chicken manure (CM) and dairy manure (DM) applied at 0 (Con), 165 (L), 335 (M), and 670 (H) kg N/ha. Means followed with different letters are significantly different at 5%

In the same field study above, sweet corn (*Zea mays* L. subsp. *mays*) percent roots at three depths (0–15, 15–30, and 30–45 cm depth) were evaluated for same animal manure types and appli‐ cation rates. The study included collecting soil cores from three locations, total of nine soil cores/plant, around the plant stem of five randomly selected plants in plots that measured 2 × 9 m each. The roots were collected from each soil core manually. As no visible roots were found in the cores collected from 30 to 45 cm depth, the results were considered for the top two depths (0–15 and 15–30 cm) only. The root percentage at the 0–15 cm depth under the CM and DM treatments was significantly (*P* < 0.05) higher than the control treatment (**Figure 9A**). However, the root percentage at the 15–30 cm depth showed the opposite pattern and root percentage under the CM and DM treatments was significantly (*P* < 0.05) lower than the control

probability based on Duncan's multiple test.

96 Organic Fertilizers - From Basic Concepts to Applied Outcomes

*3.1.2. Sweet corn root distribution*

**Figure 9.** Sweet corn root distribution (%) at two depths (0–15 and 15–30 cm) under manure type (A) and application rate (B). Means followed with different letters are significantly different at 5% probability based on Duncan's multiple test.

**Figure 10.** Sweet corn root and shoot dry weight (g/plant) under manure type (A) and application rate (B). Means fol‐ lowed with different letters are significantly different at 5% probability based on Duncan's multiple test.

#### **3.2. Livestock manure effects on sweet corn biomass**

In a field trial for two consecutive growing seasons, root and shoot biomass of sweet corn were evaluated under the application of CM and DM applied at 0 (Con), 165 (L), 335 (M), and 670 (H) kg N/ha. The analysis of variance showed a highly significant (*P* < 0.01) effect of both manure type and application rate on sweet corn root and shoot biomass. Sweet corn root biomass increased by 57% and 42% for the CM and DM treatments, respectively, compared to the control. Also, root biomass under CM was higher (10%) than DM treatment (**Figure 10A**). The shoot biomass increased by 54% and 32% for CM and DM treatments, respectively, compared to the control treatment. The shoot biomass under CM treatment was higher (17%) than DM treatment. Sweet corn root biomass increased by 42%, 20%, and 11% under high, med, and low application rates, respectively, compared to the control. Shoot biomass increased by 47%, 29%, and 13% under high, med, and low treatments, respectively, compared to the control (**Figure 10B**). The significant increase in root and shoot biomass might be related to increased nutrient availability and improved soil structure and SOM content [39]. The second‐ growing season data showed a similar pattern with higher means and no significant effect for the season on the studied parameters. The significant increase in sweet corn root and shoot biomass with the animal manure (type and rate) application is a good indicator of improved growth of sweet corn and forage produced under organic manure application, resulting in more feed for livestock and consequently more food for human consumption [28].
