Question

An ecologist was interested in the role of foliar nitrogen concentration on damage Black locust, Robinia pseudoacacia (Fabaceae) by the leaf-mining beetle Odontota dorsalis (Coleoptera: Chrysomelidae).She performed an experiment in which 24 trees were randomly assigned to two treatment groups. One treatment received an application of NPK fertilizer at 0.5kg/cm of diameter in late winter before budburst, and the other treatment received no fertilizer. Foliage was sampled at random from the tree crown of each tree at four time points during the summer season: 15 June, 15 July, 15 August, and 15 September. The average amount of damage/leaf was estimated in each sample. Use the data below to interpret the results of the experiment. Perform and interpret an appropriate test.

USE R SYNTAX

	fertilizer	june	july	august	sept
1	no	26.44296	18.56866	24.40552	16.73283
2	no	23.0431	15.23819	19.35059	24.37741
3	no	34.40666	27.806	25.7864	17.73313
4	no	24.52977	16.06204	23.66849	21.15967
5	no	24.62451	19.20965	27.50999	29.16138
6	no	27.28907	20.84593	22.38376	18.25124
7	no	21.44952	30.14457	17.83357	18.40108
8	no	21.44558	18.96957	21.49583	17.97879
9	no	25.62881	20.63632	24.08727	25.18351
10	no	24.6929	19.23125	22.84273	19.40589
11	no	23.80413	25.18506	16.5856	14.0546
12	no	24.40787	19.34779	23.70466	23.31574
13	yes	19.09894	25.25013	16.32583	21.19067
14	yes	22.95447	21.01225	19.34686	21.77521
15	yes	18.77274	23.26855	23.82966	33.39942
16	yes	23.02074	20.67915	21.21375	27.57049
17	yes	23.15637	21.75664	20.27218	26.74042
18	yes	25.07875	22.53302	20.34233	24.15076
19	yes	24.65185	24.07692	21.85248	27.64851
20	yes	21.23063	23.37344	20.75171	31.13326
21	yes	20.23226	21.79321	30.44839	21.71073
22	yes	17.70798	20.54279	21.30375	29.07599
23	yes	21.42879	22.29394	22.03362	32.19165
24	yes	24.11529	33.76621	27.05422	32.87232

Answer 1