1. 改善：meliorate 改善 | melioration 改善 | meliorative 改善的

2. 改良：melilot 草木犀 | melioration 改良 | melon 甜瓜

3. 土壤改良：Melilotus suaveolens Ledeb. 野草木樨 | melioration 土壤改良 | mellow consistency 松软结持度

noun

1. the act of relieving ills and changing for the better

Synonym: ameliorationbetterment

2. the linguistic process in which over a period of time a word grows more positive in connotation or more elevated in meaning

3. a condition superior to an earlier condition

e.g. the new school represents a great improvement

Synonym: improvement