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Long-Term Soil Experiments: Keys to Managing Earth's Rapidly Changing Ecosystems

Nicholas School of the Environ. and Earth Sci., Duke Univ., Durham, NC 27708

Mac A. Callaham, Jr.

USDA-Forest Service Southern Research Station Athens, GA 30602

David S. Powlson

Agriculture and Environment Division Rothamsted Research Harpenden, Hertfordshire AL5 2JQ UK

Pete Smith

School of Biological Sciences Univ. of Aberdeen Aberdeen, Scotland AB24 3UU UK

View larger version (25K): [in this window] [in a new window]   Fig. 1. Decadal increments in human population, 1750 to 2150 (modified from Bongaarts, 1995). Black bars of decadal increments illustrate a most critical 100 yr for human history and for soil science and management as well.

View larger version (40K): [in this window] [in a new window]   Fig. 2. (A) Global consumption of calories and protein by humanity; and (B) relative increases in protein production (open triangles and squares), compared with relative growth in human population (solid triangles or squares). In (B), the year 1961 is taken to be 1.0 (FAO, 2005).

View larger version (25K): [in this window] [in a new window]   Fig. 3. Trends in eight nations' rice yields, 1961 to 2004 (FAO, 2005). China, Indonesia, Laos, and the Philippines increased yields by threefold or more, India and Pakistan about double. Pakistan is more variable through time; Vietnam has a most impressive takeoff after 1980; and Cambodia has low stagnant yields until the mid-1990s.

View larger version (41K): [in this window] [in a new window]   Fig. 4. Dry-season rice yields during 25 yr in two experimental treatments of the long-term continuous cropping experiment at IRRI in Los Baños, Philippines. The treatments are with and without added fertilizer N.

View larger version (28K): [in this window] [in a new window]   Fig. 5. Wheat yields for >150 yr in three experimental treatments of the Broadbalk wheat experiment at Rothamsted Research, Harpenden, UK. The three treatments are: no fertilizer amendments (unmanured), inorganic fertilizer at 144 kg N ha–1yr–1, and organic farmyard manure that currently averages 240 kg N ha–1yr–1.

View larger version (18K): [in this window] [in a new window]   Fig. 6. Global C budgets for the 1990s (Houghton and Goodale, 2004). Based on fossil-fuel combustion and land-use change releases, total sources to the atmosphere were estimated at 11.5 Pg yr–1. Sinks were estimated directly except for the residual terrestrial C sink that is estimated by difference of sources and sinks. Citations are for land-use change release and uptake, and residual terrestrial sink (Houghton, 2003; Houghton and Goodale, 2004; R.A. Houghton, personal communication, 2006); fossil fuel emissions and atmospheric increase (Prentice et al., 2001); and ocean uptake (Plattner et al., 2002).

View larger version (69K): [in this window] [in a new window]   Fig. 7. Mineral-soil C (1962–2005) in old cotton fields planted in 1957 with loblolly pine (Pinus taeda L.) seedlings at the Calhoun Experimental Forest, South Carolina (Richter et al., 1999). Error bars depict spatial standard errors among the eight or 16 permanent plots (depending on year of sampling).

View larger version (60K): [in this window] [in a new window]   Fig. 8. Wheat grain 34S from Broadbalk control plots compared with annual emissions of SO2 from the UK.