What does an R-squared value of 1 mean

My research topic is relationship between soil fertility and plant growth.

The dependent variable is 1 (THT) and independent variable is 18 (soil chemists components and soil nutrients components).

And my sample is 5 plots for soil A and 13 plots for soil B.

When I use the multivariate linear regression on SPSS, the result of R-square and R is 1.000, but there is no appear a number of Adj R-square and SEE.

On the ANOVA table, still no appear a number of F. and Sig.

And the coefficients table, still no appear a number of t. and Sig.

So, what must I do?

I must add the sample or increase the independent variables?

Or, I formerly use 2 procedure :

1. t test -> Sig of variables -> regression -> pearson correlation

2. pearson correlation -> Sig variables -> regression -> t test

3. Other

If I use another software, Minitab, the result on output is different between SPSS.

So, what can I do?

Thanks.