Guano — the Andean seabird manure the Inca state rationed by law
Centuries before Europe fought over cargoes of it, the fertiliser later called guano was a regulated Andean resource. Garcilaso describes seabird-dung islands off the Peruvian coast allotted province by province, bounded with markers, and worked under a fixed quota enforced on pain of death, with the nesting birds protected the same way; Acosta gives the white dung-hills seen from the sea, the boats that went out for nothing else, and the word Guano itself. Read from the page.
Why this wins its question: Guano in English usually enters history in the 1840s, as a Victorian fertiliser mania and a Pacific war, with the Andean side reduced to "the Incas used it too". This object works the other way round and from the page: it quotes Garcilaso's 1609 account of islands allotted province by province, bounded with markers, worked under a death-penalty quota, with the birds themselves protected — and Acosta's 1590 account of the white dung-hills, the boats sent for nothing else, and the word Guano taken from the valley of Lunahuaná. Two independent sixteenth- and early-seventeenth-century witnesses, each named for the purpose he wrote to, converging on a regulated indigenous agriculture that predates every European claim on the resource.
Claims
Every assertion below is bound to registered sources and carries its own confidence. Weight them; do not treat the page as uniformly authoritative.
Garcilaso's Comentarios reales (read here in the Madrid 1829 reissue of the 1609 original, book V, chapter III) records that on the coast from below Arequipa to Tarapacá — more than two hundred leagues of shore — the only manure used on the fields was that of seabirds, "que los hay en toda la costa del Perú grandes y chicos", which flock in bands "tan grandes que son increibles sino se ven" and breed on uninhabited islets. The dung they leave is so abundant that "de lejos parecen los montones del estiercol puntas de alguna sierra nevada".
The same chapter describes a managed regime, not a free resource. In the time of the Inca kings each island was assigned by order of the Inca to particular provinces, a large island being shared among two or three; boundary markers were set so that one province's people would not cross into another's district, and each town and each household was given its measured share "tanteando la cantidad del estiercol que habia menester". On pain of death a man of one town could not take dung from another's ground, "porque era hurto", nor take from his own more than the quantity assessed as sufficient for his land; the excess was punished as an offence. Garcilaso adds that "ahora en estos tiempos se gasta de otra manera" — that under Spanish rule it was spent otherwise.
The protection extended to the birds themselves. In the breeding season no one was allowed to enter the islands on pain of life, "porque no las asombrasen y echasen de sus nidos", and it was forbidden to kill the birds at any time, inside the islands or out, under the same penalty. In some coastal valleys, Garcilaso notes, the fields were manured instead with sardine heads buried two or three to a hole with the maize seed, "y otro cualquiera dicen que antes daña que aprovecha".
Acosta's Historia natural y moral de las Indias (Seville, 1590, book IV) gives an independent description read here from the page: on some islands or farallones off the coast of Peru there appear from afar "unos cerros todos blancos", which a viewer would take for snow but which are "montones de estiercol de paxaros Marinos", built up so high — "sube varas, y aun lanças en alto" — that it seems a fabulous thing. Boats went out to these islands "a solo cargar deste estiercol", no other crop being had there, and the manured land "da el grano, y la fruta con grandes ventajas".
Acosta records the name and its origin. "Llaman Guano el dicho estiercol", he writes, from which was taken the name of the valley called Lunaguana in the valleys of Peru, "donde se aprovecha de aquel estiercol: y es el mas fertil que hay por alla". He credits it with the size and quality of the quinces, pomegranates and other fruit grown where the irrigation water passes through manured ground — the earliest printed European account read here to give the word guano and to explain its agricultural effect.
Both witnesses are participants writing to a purpose, and the object does not lean on either alone for what it cannot check. Garcilaso is a defender of Inca governance, writing decades after the fall of the state whose orderly dung-quotas he describes, and idealisation of that order is exactly his bent; Acosta frames the whole matter as the providence of the Creator, "que de tantas maneras ordena, que sirvan a los hombres las otras criaturas". What the two independently agree on — the seabird islands, the extraordinary accumulation, the deliberate agricultural use before any European named it — is firmer than what only one of them asserts about how strictly the Inca quotas were kept.
Neither source read here reaches the resource's later history, and the object does not supply from memory what the pages do not say. The nineteenth-century guano boom that made these same islands an object of international dispute, the Chincha Islands War, and the fertiliser trade that followed lie outside what a 1590 or a 1609 text can attest, and are named here only to mark the boundary of the evidence, not asserted as sourced fact.