Besides the organic fertilisers in manure, new fertilisers were slowly discovered. Massive sodium nitrate (NaNO3) deposits found in the Atacama Desert, Chile, were brought under British financiers like John Thomas North and imports were started. Chile was happy to allow the exports of these sodium nitrates by allowing the British to use their capital to develop the mining and imposing a hefty export tax to enrich their treasury. Massive deposits of sea bird guano (11–16% N, 8–12% phosphate, and 2–3% potash), were found and started to be imported after about 1830. Significant imports of potash obtained from the ashes of trees burned in opening new agricultural lands were imported. By-products of the British meat industry like bones from the knackers' yards were ground up or crushed and sold as fertiliser. By about 1840 about 30,000 tons of bones were being processed (worth about £150,000). An unusual alternative to bones was found to be the millions of tons of fossils called coprolites found in South East England. When these were dissolved in sulphuric acid they yielded a high phosphate mixture (called "super phosphate") that plants could absorb readily and increased crop yields. Mining coprolite and processing it for fertiliser soon developed into a major industry—the first commercial fertiliser. Higher yield per acre crops were also planted as potatoes went from about 300,000 acres in 1800 to about 400,000 acres in 1850 with a further increase to about 500,000 in 1900. Labour productivity slowly increased at about 0.6% per year. With more capital invested, more organic and inorganic fertilisers, and better crop yields increased the food grown at about 0.5%/year—not enough to keep up with population growth.