Higher energy prices have also made a difference as fertiliser and other input costs have risen.
The pigeon houses riddling the rock faces, traditionally used to collect the birds' droppings for use as fertiliser, mostly stand empty.
Actually cow dung is more useful, because it can be used as fertiliser.
"This phosphorous, when the manure is applied as fertiliser, actually is too high to be utilised by the crops, " he said.
Haber nitrogen was not used as fertiliser in large quantities until the middle of the 20th century, and for a good reason.
In addition, a ban on spreading slurry as fertiliser has been in place for more than three months, to avoid run-off contaminating water supplies.
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The study said improving water quality was key to controlling starfish outbreaks, with increased agricultural run-off such as fertiliser along the reef coast causing algal blooms that starfish larvae feed on.
Fertiliser, for example, would arrive late, and late fertiliser is as good as no fertiliser.
But with some exceptions Africa's governments saw the new seeds and fertiliser as a way to secure political favour, not the food supply.
Even the waste from the waste is put to good use -- the waste from the bio-fermentor is used as a natural fertiliser in the barley fields.
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Rural Affairs Secretary Richard Lochhead said increased costs, such as for fuel and fertiliser, were partly to blame for the fall last year.
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It provides loans to small farmers, trains them in agronomy and sells them seeds and fertiliser, as well as the saplings they must plant if they cut other trees down for fuel to flue-cure their crop.
It invests with Stakhanovite zeal in impressive but uneconomical facilities, such as oil refineries, steel mills and fertiliser plants.
Instead, this gas will be turned into fertiliser, or liquefied and sold as fuel.
It gobbles up gas as feedstock to make chemicals such as methanol and ammonia, a vital ingredient of fertiliser.
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China's demand for fertiliser is expected to be particularly buoyant as a result of its huge population and the poor quality of its arable land.
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Other market-oriented reforms, such as a cut in the unreasonably high subsidy on fertiliser, looked more a sop to the government's critics, and many doubt that the unpopular measure will ever obtain parliamentary approval.
As well as injecting capital, the kingdom could also offer cheap fertiliser, which it can produce by using subsidised gas.
Other South Koreans were helping to build a nuclear power plant in the North and unloading fertiliser that had been shipped from the South as aid.
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All attempts to develop Afghanistan as an agricultural exporter suffer from fundamental difficulties: lack of fertiliser and pesticides, a poor road network, shortages of electricity and cold-storage depots, and only rudimentary packaging.
While land reform is accepted by all sides as necessary in Zimbabwe, the speed of the programme has often left the land's new occupants without fertiliser, equipment and even seed.
As a result, they often forgo even the small incremental investments of which they are capable: a bit more fertiliser, some more schooling or a small amount of saving.
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