Acid soils occupy approximately 30% or 3950 m ha of the world’s ice free land area and occur mainly in two global belts where they have developed under udic or ustic moisture regimes. The northern belt (cold and temperate climate) is dominated by Spodosols, Alfisols, Inceptisols and Histosols and the southern tropical belt consists largely of Ultisols and Oxisols.

Global extent, development and economic impact of acid soils

Review of greenhouse gas emissions from crop production systems and fertilizer management effects

Nitrogen is the most limiting nutrient for crop production in many of the world's agricultural areas and its efficient use is important for the economic sustainability of cropping systems Furthermore, the dynamic nature of N and its propensity for loss from soil‐plant systems creates a unique and challenging environment for its efficient management Crop response to applied N and use efficiency are important criteria for evaluating crop N requirements for maximum economic yield Recovery of N in crop plants is usually less than 50% worldwide Low recovery of N in annual crop is associated with its loss by volatilization, leaching, surface runoff, denitrification, and plant canopy Low recovery of N is not only responsible for higher cost of crop production, but also for environmental pollution Hence, improving N use efficiency (NUE) is desirable to improve crop yields, reducing cost of production, and maintaining environmental quality To improve N efficiency in agriculture, integrated N management strategies that take into consideration improved fertilizer along with soil and crop management practices are necessary Including livestock production with cropping offers one of the best opportunities to improve NUE Synchrony of N supply with crop demand is essential in order to ensure adequate quantity of uptake and utilization and optimum yield This paper discusses N dynamics in soil‐plant systems, and outlines management options for enhancing N use by annual crops

Enhancing nitrogen use efficiency in crop plants

Invariably, many agricultural soils of the world are deficient in one or more of the essential nutrients needed to support healthy plants. Acidity, alkalinity, salinity, anthropogenic processes, nature of farming, and erosion can lead to soil degradation. Additions of fertilizers and/or amendments are essential for a proper nutrient supply and maximum yields. Estimates of overall efficiency of applied fertilizer have been reported to be about or lower than 50% for N, less than 10% for P, and about 40% for K. Plants that are efficient in absorption and utilization of nutrients greatly enhance the efficiency of applied fertilizers, reducing cost of inputs, and preventing losses of nutrients to ecosystems. Inter- and intra-specific variation for plant growth and mineral nutrient use efficiency(NUE) are known to be under genetic and physiological control and are modified by plant interactions with environmental variables. There is need for breeding programs to focus on developing cultivars with high NUE. Iden...

https://www.irrec.ifas.ufl.edu/IRSWS/History%20Publications/2/CSSPABaligar2001.pdf

Nutrient use efficiency in plants

Fast root growth responses, root exudates, and internal detoxification as clues to the mechanisms of aluminium toxicity and resistance: a review

Soil pH, soil acidity, and their effects on plants The pH scale, ranging from 0 to 14, is used to indicate acidity and alkalinity. pH is a measure of the concentration of hydrogen ions (symbol = H) in the water contained in the soil. A pH of 7.0 is neutral, values below 7 are acidic, and those above 7 are alkaline (basic). The lower the pH, the more acid the soil. Each unit pH drop indicates ten times more acidity. For example, pH 5 has 10 times more acidity than pH 6, and 100 times more acidity than pH 7. Most Hawaii soils have pH ranging from 4 to 9. For comparison, here are the pH values of some common liquids: • pure water, 7.0 • “city” water (tap water), 7.5–8 • clean rain water, about 5.6 (because of CO2 presence) • “acid rain” water, 3.5–5.5 • lemon juice, 2.2–2.4 • orange juice, 3.4–4 • vinegar, 4–4.5 • fresh milk, 6.3–6.6 • mild soap solution, 8.5–10.

Robert W. Pearson

Papers

Soil Acidity and Liming