**4. Crop responses to organic fertilizers**

Conventional farming has evoked fears of pesticide residues in food and declining energy resources [38] and organic fertilizers such as poultry litter and fish emulsions improve crop vigor and yields, increase disease and insect resistance, extend shelf life of produce and enhance microbial activity and soil nutrients [39]. Organic nutrients such as manure or cover crops provide balanced nutrient combinations over a longer period because they are slowly released based on microbial transformation in the soil [40]. Studies on the influence of poultry litter and hydrolyzed fish fertilizer on various vegetable crops to determine impact on yield and quality, phytochemical contents and on soil microbial community, and chemical proper‐ ties in the rhizospheres were conducted. These crops included Vegetable Amaranth (*Amaran‐ thus hybridus*), a leafy vegetable similar to spinach [41], Celosia (*Celosia argentea*) commonly known as lagos spinach, quail grass, soko, celosia, or feather [42], and Gboma eggplant (*Solanum macrocarpon*) is grown for its fruit production as well as its leaves [43]. West African Okra (*Abelmoschus caillei*), a multipurpose herb grown either as an annual [44], Long Bean (*Vigna unguiculata*) popular in Asian countries, African Eggplant (*Solanum aethiopicum*) is high yielding, adaptable and can be grown and harvested in a wide range of climates [44], and sweetpotato [Ipomoea batatas (L.) Lam.]. (45, 46).

#### **4.1. Materials and methods**

**Figure 7.** Distribution of Bray 1-P in poultry littered (open circle) and nonlittered (open triangle) soils. Adapted from

The USEPA required Concentrated Animal Feeding Operations (CAFO) to develop and implement Best Management Practices that minimize phosphorus and nitrogen transport from fields to surface waters. The standard requires soil phosphorus not to exceed 200 ppm by 2018 and soil with greater than 400 ppm not to receive any poultry litter applications. It is in light of these requirements of the CAFO regulations that emerged the need to develop a chemical method that would reduce phosphorus content of poultry litter before its application to agricultural land in order to avoid a long-term builds up of phosphorus in soil. An extraction procedure was developed at Tuskegee University and includes steps of equilibrating an amount of chicken litter with an extracting solution [37]. After a contact time, the solution removes a significant amount of the phosphorus from the chicken litter. The chicken litter is

Dotson, 2000.

38 Organic Fertilizers - From Basic Concepts to Applied Outcomes

Experiments were conducted on the Small Model Research Farm at the George Washington Carver Agricultural Experiment Station, Tuskegee University, on Norfolk sandy loam (fine, siliceous, thermic Typic, Paleudults) with a pH of 5.9 and organic matter content of less than 1%. The field was prepared conventionally and soil samples were collected for elemental analysis according to the method of [47] at 15 cm depths in a zig-zag pattern using an auger. The cores were composited and analyzed by the Plant and Soil Testing Laboratory at Auburn University, Alabama, USA, for mineral constituents (Ca, Mg, P, K, and pH).

Seeds for all species (or 15 cm long stem cuttings for sweetpotato) were sown in polystyrene trays filled with moistened Jiffy mix (Ferry Morse Fulton, Kentucky, USA) in a greenhouse. One seed was placed into each cell and covered with approximately 0.6 cm of medium. Trays were watered as needed and fertilized once per week with Peters 20–20–20 at the rate of 15 g per 3.78 L of water. Temperature in the greenhouse averaged about 36°C, and relative humidity and photosynthetic photon flux (PPF) were 40% and 1159 μmol/m2 s, respectively.

#### **4.2. Treatment calculations and planting**

Treatment rates for each of the six species were based on soil test recommendations. Sources of nutrients were ammonium nitrate (34% N), triple superphosphate (46% P), muriate of potash (60% K), poultry litter (54% N), and Megabloom (2% N), a fish protein fertilizer. Organic amendments were calculated based on the total N content.

Poultry litter, unlike commercial fertilizers, is quite variable and according to ref. [48] can vary up to 50% based on animal sources. The available values of litter nutrients using data from Fulhage and Pfost [47] were total N of 54 lb/ton, comprised of 48 lb/ton organic⋅N and 6 lb/ton NH4N, 59 lb/ton P2O5, and 38 lb/ton K2O. In addition, the amount of organic N available was based on days from collection to incorporation, which is 20% beyond 7 days. The calcu‐ lations were based on the following equation:

> 4 crop N - residual N available NH N + available organic N

Ten plants from each species were transplanted into three-row plots 1.2 m × 6 m at the recommended within- and between-row spacing for each species and drip irrigation applied. Fertilizer treatments for each species were based on soil test recommendations and were applied in single bands approximately 15–20 cm away from the plants. Six plants of each species from the middle row only were harvested. Physiological measurements were per‐ formed once per week, starting approximately one week after planting. These included stem diameter, plant height, and leaf area. Plant height and stem diameter were measured on each species starting at 2 cm above the soil stem interface to the terminals (for the former) and at the widest section for the latter, and recorded as cumulative growth over time. Leaf area was determined from leaf samples collected at each harvest every two weeks, using a LICOR-1800 leaf area meter (LI-COR, Lincoln, Nebraska, USA). All species were harvested periodically throughout the growing season (succulent stems of Amaranth and Celosia of approximately 15 cm length were harvested every two weeks) and once over at the end of the season. Fresh weights of harvested samples were recorded and subsamples collected for nutritional analysis. Samples were dried in ovens at 65°C for 72 h and the dry weights recorded. These data were used to estimate fresh and dry biomass yield per unit area.

The sweetpotato study was conducted as a randomized complete block design with a 4 × 4 factorial treatment arrangement in three replications. The treatment factors were conventional NPK fertilizer, poultry litter, Megabloom (fish fertilizer; FSH), and an untreated check (O). The sweetpotato cultivars were J6/66, NCC-58, TU Purple, and Whatley-Loretan. Treatments were split-applied at the rate of 134–67–67 kg/ha NPK equivalent based on soil tests recommenda‐ tions one and four weeks after planting as single bands 15 cm from the plants.

Triplicate rhizosphere soil samples from each plot were taken at harvest, composited and analyzed for pH, organic carbon (SOC), and enzyme activity. pH was determined using 1:2.5 soil/water and SOC using the wet oxidation method [49]. Phosphomonoesterases activity was determined by the method of ref. [50]; β-glucosidase and *N*-acetyl-β-glucosaminidase activity by assay [51, 52]; and whole DNA by Power Soil Extraction Kit and quantified using spectro‐ photometer. Pooled DNA samples were tested for PCR optimization and pyrosequencing analysis (Research and Testing Labs, Lubbock, TX, USA).
