Cause, conseguenze e strategie di mitigazione Proponiamo il primo di una serie di articoli in cui affronteremo l’attuale problema dei mutamenti climatici. Presentiamo il documento redatto, votato e pubblicato dall’Ipcc - Comitato intergovernativo sui cambiamenti climatici - che illustra la sintesi delle ricerche svolte su questo tema rilevante.

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Climate Change 2007: The Physical Science Basis.

http://www.irrec.ifas.ufl.edu/IRSWS/History%20Publications/2/JTEMBHe2005.pdf

Trace elements in agroecosystems and impacts on the environment

▪ Abstract Phosphorus has a number of indispensable biochemical roles, but it does not have a rapid global cycle akin to the circulations of C or N. Natural mobilization of the element, a part of the grand geotectonic denudation-uplift cycle, is slow, and low solubility of phosphates and their rapid transformation to insoluble forms make the element commonly the growth-limiting nutrient, particularly in aquatic ecosystems. Human activities have intensified releases of P. By the year 2000 the global mobilization of the nutrient has roughly tripled compared to its natural flows: Increased soil erosion and runoff from fields, recycling of crop residues and manures, discharges of urban and industrial wastes, and above all, applications of inorganic fertilizers (15 million tonnes P/year) are the major causes of this increase. Global food production is now highly dependent on the continuing use of phosphates, which account for 50–60% of all P supply; although crops use the nutrient with relatively high efficien...

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PHOSPHORUS IN THE ENVIRONMENT: Natural Flows and Human Interferences

Human actions—mining phosphorus (P) and transporting it in fertilizers, animal feeds, agricultural crops, and other products—are altering the global P cycle, causing P to accumulate in some of the world’s soil. Increasing P levels in the soil elevate the potential P runoff to aquatic ecosystems (Fluck et al. 1992, NRC 1993, USEPA 1996). Using a global budget approach, we estimate the increase in net P storage in terrestrial and freshwater ecosystems to be at least 75% greater than preindustrial levels of storage. We calculated an agricultural mass balance (budget), which indicated that a large portion of this P accumulation occurs in agricultural soils. Separate P budgets of the agricultural areas of developing and developed countries show that the rate of P accumulation is decreasing in developed nations but increasing in developing nations.

https://www.jstor.org/stable/10.1641/0006-3568(2001)051%5B0227:HIOEPA%5D2.0.CO;2

Human Impact on Erodable Phosphorus and Eutrophication: A Global Perspective

Switchgrass (Panicum virgatum L.)—a perennial, warm-season (C4) species—evolved across North America into multiple, divergent populations. The resulting natural variation within the species presents considerable morphological diversity and a wide range of adaptation. The species was adopted as a crop—initially as a forage—only in the last 50 yr. Its potential uses have recently been expanded to include biofuels. Management of switchgrass for biofuels is informed by an understanding of the plant's biology. Successful establishment requires attention to seed dormancy and weed control as well as proper depth and date of planting. The plant's growth rate is closely tied to temperature, but timing of reproductive development is linked to photoperiod. Accordingly, the period of vegetative growth can be extended by planting lower-latitude cultivars at higher latitudes. This strategy may provide a yield advantage, but cold tolerance can become limiting. Switchgrass is thrifty in its use of applied N; it appears a...

The Biology and Agronomy of Switchgrass for Biofuels

Phosphorus in agricultural runoff can cause accelerated lake and stream eutrophication. Where producers have applied P at rates exceeding crop uptake, soil P has sometimes become the main source of P in runoff. We hypothesized that soil test P (STP) correlation to dissolved reactive P (DRP) and bioavailable P (BAP) in runoff varies, depending on the extraction method. To investigate which STP extraction method would be best for predicting DRP and BAP concentration and load in runoff, soil samples were taken from the 0- to 2-cm depth of 54 grass plots (5% slopes) on Captina silt loam (fine-silty, siliceous, mesic Typic Fragiudult). The STP was extracted by six methods and the ranges of results (mg kg -1 ) were: 54-490 (Mehlich III), 27-592 (Bray-Kurtz P1), 25-169 (Olsen), 14-110 (distilled water), 23-170 (Fe oxide paper), and 105-1131 (acidified ammonium oxalate). The soil P saturation ranged from 16 to 80%. Simulated rain was applied at 100 mm h -1 and runoff was collected for 30 min. The concentration of DRP in total runoff ranged from 0.31 to 1.81 mg L -1 , and BAP from 0.37 to 2.18 mg L -1 The r 2 values for STP by each extraction method correlated with runoff DRP and BAP, respectively, were: 0.72 and 0.72 (Mehlich III), 0.75 and 0.73 (Bray-Kurtz P1), 0.72 and 0.72 (Olsen), 0.82 and 0.82 (distilled water), 0.82 and 0.82 (iron oxide paper), 0.85 and 0.82 (acidified ammonium oxalate), and 0.77 and 0.76 (P-saturation). All correlations were significant (P < 0.001), but the high r 2 values of those obtained from distilled water, iron oxide paper, and acidified ammonium oxalate extractants indicate better precision for predicting DRP and BAP concentrations in runoff. Correlations of STP with DRP load (range: 43.4 to 472.8 g ha -1 ) and BAP load (54.2 to 542.0 g ha -1 ) were not useful (r 2 < 0.18), possibly because runoff volumes were highly variable.

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Relating Extractable Soil Phosphorus to Phosphorus Losses in Runoff

Phosphorus movement in runoff often promotes algal growth in lakes. Thus, agricultural soils and management practices that enhance the potential for P movement must be identified. The main factors controlling P movement are transport (runoff and erosion potential) and source factors (surface soil P and method, rate, and timing of fertilizer and animal manure applications). Implementation of management that minimizes runoff and erosion will reduce P transport in runoff, although total algal availability can increase. The continued application of P has increased surface soil test P contents in excess of levels sufficient for optimum crop yields. Although increases in soil P have been related to P enrichment of runoff in plot and watershed studies, information for given management systems still is needed to reliably quantify critical soil P levels above which excessive P enrichment of runoff will occur [...]

Phosphorus Movement in the Landscape

Information on the forms and sources of P, the importance of minimizing P in surface waters, procedures for identifying P-sensitive water bodies, and management approaches that limit P loss is presented.

Minimizing surface water eutrophication from agriculture by phosphorus management

Aluminum sulfate [Al 2 (SO 4 ) 3 - 14H 2 O] applications to poultry litter can greatly reduce P concentrations in runoff from fields fertilized with poultry litter, as well as decrease NH 3 volatilization. The objective of this study was to evaluate metal runoff from plots fertilized with varying rates of alum-treated and untreated (normal) poultry litter. Alum-treated (10% alum by weight) and untreated litter was broadcast applied to small plots in tall fescue (Festuca arundinacea Schreb.). Litter application rates were 0, 2.24, 4.49, 6.73, and 8.98 Mg ha -1 (0, 1, 2, 3, and 4 tons acre -1 ). Rainfall simulators were used to produce two runoff events, immediately after litter application and 7 d later. Both concentrations and loads of water-soluble metals increased linearly with litter application rates, regardless of litter type. Alum treatment reduced concentrations of As, Cu, Fe, and Zn, relative to untreated litter, whereas it increased Ca and Mg. Copper concentrations in runoff water from untreated litter were extremely high (up to 1 mg Cu L), indicating a potential water quality problem. Soluble Al, K, and Na concentrations were not significantly affected by the type of litter. Reductions in trace metal runoff due to alum appeared to be related to the concentration of soluble organic C (SOC), as well as the affinity of SOC for trace metals. Metal runoff from alum-treated litter is less likely to cause environmental problems than untreated litter, since threats to the aquatic environment by Ca and Mg are far less than those posed by As, Cu, and Zn.

Decreasing Metal Runoff from Poultry Litter with Aluminum Sulfate

Rainfall simulators have a long history of successful use in both laboratory and field investigations. Many
plot–scale simulators, however, have been difficult to operate and transport in the field, especially in remote locations where
water or electricity is unavailable. This article describes a new rainfall simulator that is relatively easy to operate and
transport to and from the field while maintaining critical intensity, distribution, and energy characteristics of natural rainfall.
The simulator frame is constructed from lightweight aluminum pipe with a single 50 WSQ nozzle centered at a height of 3 m
(9.8 ft). An operating nozzle pressure of 28 kPa (4.1 psi) yields continuous flow at an intensity of 70 mm h –1 (2.8 in. h –1 ) over
a 1.5– U 2–m (4.9– U 6.6–ft) plot area with a coefficient of uniformity of 93%. Kinetic energy of the rainfall is about
25 J m –2 mm –1 (142.8 ft–lb ft –2 in. –1 ), approximately 87% of natural rainfall. The simulator can be easily transported by two
field personnel and completely assembled or disassembled in approximately 10 min. Water usage is at a minimum as the
simulator utilizes only one nozzle.

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Dwayne R. Edwards

Papers

Relating Extractable Soil Phosphorus to Phosphorus Losses in Runoff

Phosphorus Movement in the Landscape

Minimizing surface water eutrophication from agriculture by phosphorus management

Decreasing Metal Runoff from Poultry Litter with Aluminum Sulfate

A Portable Rainfall Simulator for Plot-Scale Runoff Studies