(1) analysis results: the planting depth is 6 cm; 1 1cm； 18cm； The number of unearthed seedlings in 25cm is: 29; 30 trees; 26 trees; It can be seen from 20 trees that when the planting depth of mung bean seeds exceeds 1 1cm, the emergence rate will decrease with the increase of planting depth, because the emergence needs sufficient nutrients. If the planting depth is too deep, the nutrients in the cotyledons are not enough to emerge.

(2) Analysis of experimental results: The leaf size of seedlings in group A, group B, group C and group D is larger; Smaller; Only traces; Only traces. In this way, the seedlings of group A can be used to promote the development of seedlings, and the seedlings can grow new leaves earlier, carry out photosynthesis and accumulate organic matter. Therefore, on day 15, 10 seedlings of group A, group B, group C and group D were taken, and the organic content of each group was determined respectively, and the organic content of group A was the highest.

So the answer is: (1) decline; The nutrients in cotyledons are not enough for seedlings to be unearthed; (2) answer.