The main nitrogen fertilizer field crops, cash crops such as vegetables, tobacco, grapes, cotton, etc., in addition to nitrogen also applying potassium fertilizer. For example, spring corn crops are treated with urea one-time base fertilizer as a reference.
　　
The other half of the urea was topdressed and applied at the end of July and early August. The latter's nitrogen fertilizer utilization rate can be increased by 10% to 20% . This indicates that the utilization rate of nitrogen fertilizer application is significantly higher than that of all nitrogen fertilizers. on Nitrogen and potassium fertilizers must be applied in the summer to avoid soil nitrogen loss caused by nitrogen fertilizer application and potassium fixation caused by potassium and fertilizer on the surface due to alternating wet and dry.A dumbwaiter is a small freight elevator or lift intended to carry objects rather than people. Dumbwaiters found within modern structures, including both commercial, public and private buildings, are often connected between multiple floors. When installed in restaurants, schools, kindergartens, hospitals, retirement homes or in private homes, the lifts generally terminate in a kitchen.
The term seems to have been popularized in the United States in the 1840s, after the model of earlier "dumbwaiters" now known as serving trays and lazy Susans. The mechanical dumbwaiter was invented by George W. Cannon, a New York City inventor. Cannon first filed for the patent of a brake system (US Patent no. 260776) that could be used for a dumbwaiter on January 6, 1883. Cannon later filed for the patent on the mechanical dumbwaiter (US Patent No. 361268) on February 17, 1887.Cannon reportedly generated a vast amount of royalties from the dumbwaiter patents until his death in 1897.
A simple dumbwaiter is a movable frame in a shaft, dropped by a rope on a pulley, guided by rails; most dumbwaiters have a shaft, cart, and capacity smaller than those of passenger elevators, usually 45 to 450 kg (100 to 1000 lbs.) Before electric motors were added in the 1920s, dumbwaiters were controlled manually by ropes on pulleys.
Early 20th-century codes sometimes required fireproof dumbwaiter walls and self-closing fireproof doors and mention features such as buttons to control movement between floors and locks on doors preventing them from opening unless the cart is stopped at that floor. Dumbwaiter Lifts in London were extremely popular in the houses of the rich and privileged. Maids would use them to deliver laundry to the laundry room from different rooms in the house. They negated the need to carry handfuls of dirty washing through the house, saving time and preventing injury.
A legal complaint about a Manhattan restaurant's dumbwaiter in 1915, which also mentions that food orders are shouted up and down the shaft, describes its operation and limitations as follows:
[There is] ... great play between the cart of the dumb-waiter and the guides on which it runs, with the result that the running of the cart is accompanied by a loud noise. The rope which operates the cart of the dumb-waiter runs in a wheel with a very shallow groove, so that the rope is liable to and does at times slip off. ... The cart has no shock absorbers at the top, so that when it strikes the top of the shaft or wheel there is a loud report. ... [T]he ropes of the dumb-waiter strike such wall at frequent intervals with a loud report. ... [T]he dumb-waiter is often negligently operated, by running it faster than necessary, and by letting it go down with a sudden fall.
More recent dumbwaiters can be more sophisticated, using electric motors, automatic control systems, and custom freight containers of other kinds of elevators. Recently constructed book lifts in libraries and mail or other freight transports in office towers may be larger than many dumbwaiters in public restaurants and private homes, supporting loads as heavy as 450 kg (990lbs)
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