Amjad A. Ahmad

Nutrient concentrations within and below root zones from applied chicken manure in selected Hawaiian soils

The objective of this study was to evaluate the effects of chicken manure (CM) application rates on nutrient concentrations within and below the root zone of sweet corn (Zea mays L. subsp. mays) under Hawaiian conditions. The research was conducted in leeward (Poamoho) and windward (Waimanalo) areas of Oahu, Hawaii, where contrasts exist in both climatic and soil conditions. Suction cup were used to collect soil solutions from 30 and 60 cm depths. Soil solutions were collected six times during the growing season at each location and analyzed for different nutrients (N, P, K, Ca, Mg, Na, Fe, Mn, Zn, and Cu), nitrate-nitrogen (NO3–N), ammonium-nitrogen (NH4–N), electrical conductivity (EC), and pH. Analysis showed that CM rates significantly affected the concentration of macro-nutrients below the root zone at Poamoho and within the root zone at Waimanalo. In general, nutrient concentration increased with the increasing rates of CM application. There was a significant effect of CM on micro-nutrients except below the root zone at Poamoho. CM significantly affected NO3–N concentration within the root zone for 15, 60 days after planting (DAP) at Poamoho, and 16, 28 DAP at Waimanalo. The effect was also significant on total nitrogen (N) concentration in the root zone across the two growing seasons at Waimanalo. There was a highly significant correlation between total N and NO3–N, and EC within and below the root zone.

Nitrogen Release Patterns of Some Locally Made Composts and Their Effects on the Growth of Chinese Cabbage (Brassica Rapa, Chinensis Group) When Used as Soil Amendments

ABSTRACT. Due to strong demands from organic farmers, landscapers, and home-gardeners, production and utilization of composts have rapidly increased. So, there is the need for their characterization (compost quality evaluations, particularly their nutrient releasing characteristics). In this study, three vermi-composts, six thermo-composts, and a green manure were incubated at 10 g/kg with a Mollisol and an Oxisol at room temperature. Unamended soils served as controls. Nitrate (NO3-N) was extracted and measured at 3, 7, 14, 21, 28, 42, and 56 days during the incubation. The results showed that the potentially mineralizable N (referred to as N0) varied widely among the composts, but the mineralization rate (k) remained nearly constant, ranging from 0.02 to 0.03/day, suggesting that approximately 2 to 3% of N0 was transformed into NO3-N per day. Cumulative NO3-N release was linearly related to the square root of the total N in the composts. Relative absorbance at 260 nm of a 0.01M NaHCO3 extract failed to predict N0, but could clearly separate vermi-composts (low absorbance readings) from thermo-composts (high absorbance). A subsequent greenhouse experiment using pak choi (Brassica rapa, Chinensis group, cv. Bonzai) as the test plant grown on the same two soils amended with 10 g/kg composts or green manure demonstrated the beneficial effects of the organic inputs when compared with the control (soil alone) or a complete mineral fertilizer treatment (providing 80 mg N/kg as 16-16-16 commercial fertilizer with 0.5% micronutrients). Organic amendments provided more benefits to cabbage growth in the infertile yet better drained Oxisol than in the fertile but poorly drained Mollisol.

Nitrate Dynamic in a Tropical Mollisol Amended with Organic Manures, Planted with Sweet Corn, and Monitored with SPAD Readings

Two field experiments were conducted to evaluate the use of relative chlorophyll content (RCC) in sweet corn leaves as an indicator of nitrate concentration in soil. Study objectives were (1) to evaluate the effect of manure types (chicken and dairy), rates (0, 168, 336, and 672 kg ha−1 equivalent N), and application frequency (one and two applications) of organic amendments on (a) nitrate nitrogen (NO3-N) concentration within and below the crop root zone and (b) the RCC of sweet corn leaves and (2) to quantify the relationship between RCC and NO3-N concentrations. The results showed a significant increase in NO3-N concentrations within and below the root zone and plant leaf RCC under chicken manure treatments. Manure application rates and frequency had a significant effect on both NO3-N concentration within and below the root zone and leaf RCC. It appears that leaf RCC can be used as an indicator of NO3-N availability for sweet corn cultivated under the study conditions.

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

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 Hawaiis 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.

A Correlation of Rapid Cardy Meter Sap Test and ICP Spectrometry of Dry Tissue for Measuring Potassium (K+) Concentrations in Pak Choi (Brassica Rapa Chinensis Group)

ABSTRACT Nutritional status of vegetable crops is often monitored by analysis of dried plant tissues, which is costly and often time consuming. Two greenhouse trials were conducted, at the University of Hawaii at Manoa, Magoon facilities, to evaluate the portable cardy ion meter (CIM) in determining potassium (K+) status in fresh petiole sap of pak choi as compared with standard laboratory methods. In the first greenhouse trial, three algae species (Gracilaria salicornia, Kappaphycus alvarezii, and Eucheuma denticulatum) were used to apply five rates of K+ (0, 84, 168,252, and 336 kg.ha−1). The pak choi was directly seeded into 4 L pots and was grown in peat moss. In the second greenhouse trial, K+ was provided through Eucheuma denticulatum and potassium nitrate (KNO3) at five rates (0,112, 168, 224, 280, and 336 kg.ha−1) in peat moss and soil media. At harvest, K+ concentrations in fresh petiole sap were analyzed immediately with CIM and the dried samples were analyzed by inductively coupled plasma spectroscopy (ICP) measurement. The results showed increase in leaf K+ content at higher rates and the maximum concentration of leaf K+ at 4500–5300 mg/L for sap and 8–9% for tissue was obtained when K+ was provided between 224 and 284 kg.ha−1. There was a close correlation between the CIM readings and the ICP method (r = 0.8048 and 0.8314) from the first and second GH results, respectively. The results suggest that the CIM could be used for the rapid monitoring of the relative K+ status of plants. The data further suggested 4500–5000 mg K/L for fresh petiole sap and 7.5% K+ in tissue as critical levels for K+ concentration in pak choi.

Effect of Intercropping Three Legume Species on Growth and Yield of Sweet Corn (Zea mays) in Hawaii

In Hawaii, there are many small farm holders. Intercropping may increase diversity of farm products, reduce input costs, and increase farm profitability. Two field experiments were conducted in Hawaii to study the effect of three legume species intercropped with sweet corn (Zea mays L.) on the growth, relative chlorophyll content, biomass, and yield of sweet corn. The treatments included corn + soybean (CS), corn + bush bean (CB), corn + cowpea (CC), and corn alone (CO; control). In the first growing season, 30 days after planting, relative chlorophyll content of corn leaves was significantly higher in CC treatment with 53%, 56%, and 68% compared with CB, CS, and CO, respectively. While, in the second growing season, 30 days after planting, relative chlorophyll content of corn leaves was significantly higher in CC treatment with and 31%, 33%, and 66% compared with CB, CS, and CO, respectively. Corn plants in the CC treatment were significantly taller and had greater leaf area than those in other treatments. Fresh and dry weights of corn biomass, corn + legume biomass (with and without pods), and fresh weight of corn ears were all significantly higher for the CC treatment as compared with the other treatments. Mean fresh weight of corn ears under CC treatment increased by 9.9%, 35.1%, and 53.5% compared with CB, CS, and CO, respectively. The results suggested that lower competition and/or the contribution of fixed N in the CC treatment contributed to the better growth of corn.