**4. Algae species**

**Figure 10.** Sweet corn root and shoot dry weight (g/plant) under manure type (A) and application rate (B). Means fol‐

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,

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**

98 Organic Fertilizers - From Basic Concepts to Applied Outcomes

Hawaii imports about 85% of the food consumed in the state, leaving it extremely vulnerable in terms of food safety and global events [40]. High level of goods imported and distributed throughout the state also poses a threat of introduced invasive plants (**Figure 11**) and animals [41, 42]. Marine non‐native invasive seaweed has proven to be very costly to control in addition to developing a threat to the marine native ecosystem [43, 44]. The non‐native seaweed species that have settled along the reefs of Hawaii grow and propagate more readily than the native seaweeds in Hawaii [45]. This is most likely because these seaweeds have less natural predators and herbivorous grazers since they are non‐native to the area. Below is a description of the most common seaweed species found in Hawaii.

**Figure 11.** *Eucheuma* spp. sample collected on Oahu Island.

*Gracilaria salicornia*, also known as the Giant Ogo, is one of the most successful invasive seaweed species in Hawaii and is found mostly on Oahu and Hawaii Island. *G. salicornia* was first discovered in Hilo Bay on Hawaii Island and is believed to have originated somewhere throughout the Indian and Pacific Oceans [46]. This seaweed is much fitter than the native seaweeds and is more tolerant to light adjustments. It forms a thick mat that inhibits the growth of native seaweed species. This seaweed propagates both sexually and asexually by cloning through the fragmentation process [47].

*Kappaphycus* spp. (*K. striatum* and *K. alvarezii*) are coarse, spiny, and invasive seaweed and are usually dark green in color but may appear red if shaded. It was first introduced in Kaneohe Bay, Oahu, in 1979 for experimental aquaculture. This seaweed mostly resides in shallow subtidal reef flats in Kaneohe Bay on Oahu. Its fast vegetative growth increases with the environmental temperatures, allowing it to reproduce very rapidly [46] (http:// www.botany.hawaii.edu/invasive).

*Eucheuma* spp. (*E. dentriculatum* and *E.* spp.) are much like *K.* spp. characteristics that make them difficult to distinguish between species. Rather, the term (clades) has been used to describe the physically different *E.* spp. without the use of molecular markers to distinguish between types. These types are commonly found on the east shores of Oahu Island as well as in the Waikiki area in Honolulu [48].

*Avrainvillea amadelpha*, also known as the mud weed, consists of wedge‐shaped blades that are thin, diaphanous, 1–3 cm tall, and 1–4 cm wide. It has a dense cluster shape from attaching the blades by stalk to a compact basal holdfast. Blades are green to green‐gray in color with smooth to lacerated edges. Clumps are muddy brown from being covered with silty sand. In Hawaii, *A. amadelpha* can be found in abundance on the shallow reef flats of Oahu's south shores, where it has disturbed and replaced native seaweed beds. It is expected to be a natural component of the deep‐water community in Hawaii (http://www.botany.hawaii.edu/invasive).

*Acanthophora spicifera* seaweeds are abundantly found on calm, shallow reef flats, tide pools, and rocky intertidal benches. Often free floating, much of the success of these seaweeds is credited toward its brittle nature, allowing more widespread asexual distribution. The success of these seaweeds has contributed to the displacement of the native species of seaweeds. Evidence of its success in Hawaii is found in Maui, Molokai, Lanai, Kohoolawe, Oahu, and Kauai Islands (http://www.botany.hawaii.edu/invasive).

*Hypnea musciformis* is mostly recognized by its broad curls at the ends of some branches, allowing it to twine around other seaweeds. *H. musciformis* seaweeds are usually red in color but can also be yellow to brown in high‐light environments or nutrient poor waters. During the bloom stage, it may be found free floating but is otherwise found on intertidal and shallow subtidal reef flats, tidepools, and rocky benches. It tends to grow on other large seaweeds and reproduces by fragmentation. These invasive seaweeds are destructive because they grow much faster than the native seaweed and shade out coral (http://www.botany.hawaii.edu/ invasive).

The species that are currently targeted by cleanup efforts on Oahu Island are *G. salicornia*, *K*. spp., and *E.* spp. [49]. These species are predominantly found in Kaneohe Bay, reproduce asexually, and have not been observed to reproduce sexually in Hawaii. However, they are very capable of dominating the reefs with fragments of 0.5 cm and bigger [46, 50]. Some species of invasive seaweed have shown potential for use as an agricultural amendment due to its


high K (13.5–18%) content (**Table 4**) and provide an opportunity to utilize an otherwise ecologically disruptive species.

Washing was by soaking each sample in a bucket of tap water for 3 minutes. Each value is a mean of three values.

**Table 4.** Seaweed species macro‐ and micro‐nutrient content (with and without washing).

#### **4.1. Nutrient variability and bio‐security protocol for algae**

#### *4.1.1. Nutrient variability among algae species*

seaweeds and is more tolerant to light adjustments. It forms a thick mat that inhibits the growth of native seaweed species. This seaweed propagates both sexually and asexually by cloning

*Kappaphycus* spp. (*K. striatum* and *K. alvarezii*) are coarse, spiny, and invasive seaweed and are usually dark green in color but may appear red if shaded. It was first introduced in Kaneohe Bay, Oahu, in 1979 for experimental aquaculture. This seaweed mostly resides in shallow subtidal reef flats in Kaneohe Bay on Oahu. Its fast vegetative growth increases with the environmental temperatures, allowing it to reproduce very rapidly [46] (http://

*Eucheuma* spp. (*E. dentriculatum* and *E.* spp.) are much like *K.* spp. characteristics that make them difficult to distinguish between species. Rather, the term (clades) has been used to describe the physically different *E.* spp. without the use of molecular markers to distinguish between types. These types are commonly found on the east shores of Oahu Island as well as

*Avrainvillea amadelpha*, also known as the mud weed, consists of wedge‐shaped blades that are thin, diaphanous, 1–3 cm tall, and 1–4 cm wide. It has a dense cluster shape from attaching the blades by stalk to a compact basal holdfast. Blades are green to green‐gray in color with smooth to lacerated edges. Clumps are muddy brown from being covered with silty sand. In Hawaii, *A. amadelpha* can be found in abundance on the shallow reef flats of Oahu's south shores, where it has disturbed and replaced native seaweed beds. It is expected to be a natural component

*Acanthophora spicifera* seaweeds are abundantly found on calm, shallow reef flats, tide pools, and rocky intertidal benches. Often free floating, much of the success of these seaweeds is credited toward its brittle nature, allowing more widespread asexual distribution. The success of these seaweeds has contributed to the displacement of the native species of seaweeds. Evidence of its success in Hawaii is found in Maui, Molokai, Lanai, Kohoolawe, Oahu, and

*Hypnea musciformis* is mostly recognized by its broad curls at the ends of some branches, allowing it to twine around other seaweeds. *H. musciformis* seaweeds are usually red in color but can also be yellow to brown in high‐light environments or nutrient poor waters. During the bloom stage, it may be found free floating but is otherwise found on intertidal and shallow subtidal reef flats, tidepools, and rocky benches. It tends to grow on other large seaweeds and reproduces by fragmentation. These invasive seaweeds are destructive because they grow much faster than the native seaweed and shade out coral (http://www.botany.hawaii.edu/

The species that are currently targeted by cleanup efforts on Oahu Island are *G. salicornia*, *K*. spp., and *E.* spp. [49]. These species are predominantly found in Kaneohe Bay, reproduce asexually, and have not been observed to reproduce sexually in Hawaii. However, they are very capable of dominating the reefs with fragments of 0.5 cm and bigger [46, 50]. Some species of invasive seaweed have shown potential for use as an agricultural amendment due to its

of the deep‐water community in Hawaii (http://www.botany.hawaii.edu/invasive).

Kauai Islands (http://www.botany.hawaii.edu/invasive).

through the fragmentation process [47].

100 Organic Fertilizers - From Basic Concepts to Applied Outcomes

www.botany.hawaii.edu/invasive).

in the Waikiki area in Honolulu [48].

invasive).

Different batches of the four main species (*G. salicornia*, *Kappaphycus* spp., *Eucheuma* spp., and *A. amadelpha*) were collected from the Department of Land and Natural Resources (DLNR) "SuperSucker" team on Oahu at Kaneohe Bay. To reduce the salt content from the seaweeds and to evaluate the washing effect on nutrient content, the samples were split into two portions. One portion was washed with tap water, by soaking the sample in a bucket for 3 minutes. The other half was not washed. The two portions were dried at 95°C for 96 hours, and three subsamples of washed and not washed species of nutrient contents were determined. The results (**Table 4**) showed a high content of K in the *E.* spp. (18.02%), *K*. spp. (14.81%), and *G. salicornia* (12.4%). However, *A. amadelpha* was found to contain 0.36% K only, but a high content of Ca was 30.13%. Also, all species had a relatively good amount of N and other macro‐ and micro‐nutrients beneficial for plant growth, yield, and rebuilding soil fertility [51]. Washing decreased the content of all macro‐ and micro‐nutrients of all four species. However, the nutrient loss did not reach a significant level, and it is believed to significantly reduce the sodium content.

#### *4.1.2. Viability and bio‐security protocol*

Viability and the spread of alien algae species into new shores and beaches across the Hawaiian Islands is a major concern and limitations to the use of these species as a major organic source of K fertilizer in agriculture, especially for direct application (without composting). A lab experiment was conducted to evaluate the effect of time and temperature on four seaweed species (*K.* spp., *E.* spp., *G. salicornia*, and *A. amadelpha*). The samples were dried in a conven‐ tional oven at ∼90°C for 3 or 4 days (72 and 96 hours). Viability of dried samples was tested in a lab experiment with fresh (tap) and salt (ocean) water. Three random samples of 10 g from each species were placed in a 200 ml beaker with 100 ml of fresh or salt water. The lab experi‐ ment was repeated twice for 2 weeks each time. Monitoring changes on the seaweed species was performed over the 2‐week test duration by taking pictures for each subsample. The results were identical for the repeated experiment. In both trials, the four seaweed species show no signs of growth or changes in volume, as a sign of water absorption during the first week. In the second week, the species showed decomposition signs (**Figure 12**). No differences were found between drying the samples for 72 or 96 hours and soaking the subsamples in fresh or salt water.

**Figure 12.** The four algae species showing signs of decomposition at the end of the second test experiment.

#### **4.2. Direct application as organic source of potassium**

Two field trials were conducted to evaluate the effect of different application rates of K on sweet potato growth and yield. K was applied at four application rates (0, 55, 110, and 220 kg  K/ha) under two soil series (Wahiawa and Waialua). The experiment was under RCBD with three replicates. At harvest, the tuber fresh weight was recorded. Harvested tubers were cut down to pieces and dried at 75°C for 72 hours and then dry weight was recorded. The analysis of variance showed a highly (*P* < 0.01) significant effect of K application rates on the fresh and dry weights of sweet potato tubers. The highest means were at 220 kg K/ha, and the lowest was in the control (**Figure 13A** and **B**). The results were similar in pattern for both soils. However, the fresh and dry weights of tubers were higher in the Oxisol (Wahiawa series) soil than the Mollisol (Waialua series) soil, although the Mollisol is thought to have higher fertility than the Oxisol soil that might be related to the differences in structure between the two soils [22]. The initial K content in the two soils was higher than 300 ppm. However, the application showed a significant effect on the sweet potato growth and yield. This suggested that the soil K might not be available to the plant [52], and/or that the seaweed application improved the SOM, and/or the improvement in soil physical properties [53], allowing good tuber growth.

Use of Organic Fertilizers to Enhance Soil Fertility, Plant Growth, and Yield in a Tropical Environment http://dx.doi.org/ 10.5772/62529 103

experiment was conducted to evaluate the effect of time and temperature on four seaweed species (*K.* spp., *E.* spp., *G. salicornia*, and *A. amadelpha*). The samples were dried in a conven‐ tional oven at ∼90°C for 3 or 4 days (72 and 96 hours). Viability of dried samples was tested in a lab experiment with fresh (tap) and salt (ocean) water. Three random samples of 10 g from each species were placed in a 200 ml beaker with 100 ml of fresh or salt water. The lab experi‐ ment was repeated twice for 2 weeks each time. Monitoring changes on the seaweed species was performed over the 2‐week test duration by taking pictures for each subsample. The results were identical for the repeated experiment. In both trials, the four seaweed species show no signs of growth or changes in volume, as a sign of water absorption during the first week. In the second week, the species showed decomposition signs (**Figure 12**). No differences were found between drying the samples for 72 or 96 hours and soaking the subsamples in fresh or

**Figure 12.** The four algae species showing signs of decomposition at the end of the second test experiment.

Two field trials were conducted to evaluate the effect of different application rates of K on sweet potato growth and yield. K was applied at four application rates (0, 55, 110, and 220 kg  K/ha) under two soil series (Wahiawa and Waialua). The experiment was under RCBD with three replicates. At harvest, the tuber fresh weight was recorded. Harvested tubers were cut down to pieces and dried at 75°C for 72 hours and then dry weight was recorded. The analysis of variance showed a highly (*P* < 0.01) significant effect of K application rates on the fresh and dry weights of sweet potato tubers. The highest means were at 220 kg K/ha, and the lowest was in the control (**Figure 13A** and **B**). The results were similar in pattern for both soils. However, the fresh and dry weights of tubers were higher in the Oxisol (Wahiawa series) soil than the Mollisol (Waialua series) soil, although the Mollisol is thought to have higher fertility than the Oxisol soil that might be related to the differences in structure between the two soils [22]. The initial K content in the two soils was higher than 300 ppm. However, the application showed a significant effect on the sweet potato growth and yield. This suggested that the soil K might not be available to the plant [52], and/or that the seaweed application improved the SOM, and/or the improvement in soil physical properties [53], allowing good tuber growth.

**4.2. Direct application as organic source of potassium**

102 Organic Fertilizers - From Basic Concepts to Applied Outcomes

salt water.

**Figure 13.** The effect of different potassium (K) application rates (kg K/ha) on average sweet potato tuber fresh (A) and dry (B) weight under Oxisol and Mollisol soils.
