Why does Vayikra 25:3 repeat “שש שנים”?

Question

In Vayikra 25:3 it says:

שש שנים תזרע שדך ושש שנים תזמור כרמך

Why does it say twice שש שנים ?

Answer 1

in the Sifra (Behar):

יכול אף על פי שלא השרישו? תלמוד לומר שש שנים תזרע שדך... ואספת ששה זרעים וששה אסיפים לא שישה זרעים ושבעה אסיפים

To understand the Midrash Tanaim, I looked in the commentary of Rabbi Aaron Iben Chaim - called "Korban Haaron" (Lived in Fez about four hundred and fifty years) the book is strongly recommended. The Sifra ask: Can we pick up (in the seventh year) all the corn planted in the sixth year? answer : six year it says twice, the second "שש שנים" return to the Continuation of the verse "ואספת", such written "ושש שנים ואספת" , you can pick up only six years and not seven years, If the corn is not rooted.

Because the book is not common I am attaching a picture of him :

Answer 2

There is certainly a derasha, as given in the other answer. But on a peshat level, there is also a straightforward answer. It is beautiful and poetic. And it resonates. There is a certain Biblical style here, carried through in the next phrases and in the next verses. This is carried out by meter, syllable count, by parallelism, and repeated syntactic structure within the parallelism.

Thus,
a) שֵׁשׁ שָׁנִים תִּזְרַע שָׂדֶךָ
b) וְשֵׁשׁ שָׁנִים תִּזְמֹר כַּרְמֶךָ
and applying to both
c) וְאָסַפְתָּ, אֶת-תְּבוּאָתָהּ

and
a) וּבַשָּׁנָה הַשְּׁבִיעִת
which applies to
b) שַׁבַּת שַׁבָּתוֹן יִהְיֶה לָאָרֶץ
c) שַׁבָּת, לַיהוָה

and then, repeated examples in conclusion:
a) שָׂדְךָ לֹא תִזְרָע
b) וְכַרְמְךָ לֹא תִזְמֹר.

Next,
אֵת סְפִיחַ קְצִירְךָ לֹא תִקְצוֹר
וְאֶת-עִנְּבֵי נְזִירֶךָ לֹא תִבְצֹר
and in conclusion:
שְׁנַת שַׁבָּתוֹן, יִהְיֶה לָאָרֶץ

The alternative would involve less words, but would not resonate nearly so well.