In the tenancy security system (yazuzhi 押租制), tenant farmers (diannong 佃農) had to hand over a certain sum of money to the landowner as a deposit to vouch for the rent in situations when they would be unable to or refused to pay the rent. This deposit was variously called yazu 押租, yadian 押佃, dingshou 頂首, dingshou 頂手, dingpi 頂批, dinggen 頂耕, dingzhong 頂種, dingdian 頂佃, dingjia 頂價, puyin 贌銀, jiayin 價銀, dianjia 佃價, dianli 佃禮, diangui 佃規, diantou 佃頭, dianshou 佃手, pitou 批頭, pili 批禮, jizhuang 寄莊, jinzhuang 進莊, jinzhuangli 進莊禮, shanzhuang 上莊, zhuangdian 莊佃, landian 攬佃, lanzhong 攬種, lanzu 攬租, baodian 保佃, baozu 保租, yadian 壓佃, tiangen 田根, qigeng 起埂, diandian 典佃, xietianli 寫田禮, chengtian 承佃, cheshou 扯手, wenzu 穩租, fenzhi 糞質, fenwei 糞尾, duojiao 墮腳, suijiao 隨腳, jijiao 基腳, guajiao 掛腳, tuojian 脫肩 or duogeng 墜耕.
The custom emerged during the Ming period 明 (1368-1644) and is attested in contracts from the Wanli reign-period 萬曆 (1573-1619) where the formula "[the tenant] handed over a sum for security" (jiaoji yazu qianwen 交繳押租錢文) is regularly seen. In documents from Xinghua 興化, Fujian, the formula "with security as supplement for [outstanding] rent" (you tiangenyin, dibu zu 有田根銀，抵捕租) was used.
The invention of the security system goes back to the increasing monetization of the Chinese economy and the gradual dissolution of the serf system which had until then been common. Some economists interpret the security as a replacement for the services the peasants once had to deliver to the landowner in earlier times. Yet the emergence of a security might also have been influenced by population growth and the concentration of land ownership in the hands of a few members of the gentry. In the early 19th century, the deposit system was found in practically all provinces of China proper, and found entrance to the border regions in the early years of the Republic (1911-1949). In the 1930s, as much as 70-80 per cent of tenant farmers had to pay a deposit to the landowners (Jiang 1995).
The height of the security depended on the sum of the rent, the fertility of the soil, and the size of the farmer household. It was higher in regions of rich soil and dense population. The sum often surpassed the rent of one year, in serious cases up to seven or eight times or even more (Jiang 1992), and was not expected to yield interest. In cases the tenant farmer was not able to pay his rent, the land owner would deduct that sum from the security. Normally, the land owner would pay back the security when a tenant's contract ended, but if the sum was relatively low (in Hunan called xiaoxie 小寫), he might also refuse back payment. On the other hand, the tenant might cut short the rent if the security sum was too high, a phenomenon characterized by the rule "high security means low rent, and high rent lower security" (ya zhong zu qing, ya qing zu zhong 押重租輕，押輕租重).
As both sides were bound by contract, a land owner could not lease out the land to another person before the contract period ended or the security was paid back, but in some regions, tenant farmers were allowed to rent out land to a third party. In any case, the existence of the deposit prevented to a certain extent the mobility of peasant families and cemented social structures in the countryside.
Shortage in land was one reason that it was difficult for small-scale tenant farmers to hand over the sums requested for deposits. Landowners therefore usually allowed to count the deposit as a kind of credit which the farmers would have to pay back in the years to come. Landowners did this either by requesting exorbitant interest on the principal or substantially increased the rent. This kind of debt trap was the main reason for the widespread impoverishment of tenant farmers in the first half of the 20th century.