I would like to bring here in short what Reb Chaim of Brisk said about this particular Rambam and the argument between the Gra and the Kesef Mishna about its meaning. The Rambam himself says if a gentile owns land in Israel then when a jew buys it back from him the produce will be obligated in truma and maasar. The Kesef Mishna says the meaning is that bot the land and produce need to be in the possession of the Jew when the produce reaches a third of its growth in order to be obligated in truma. Reb Chaim says the reason for the Rambam and the Kesef Mishna is that you need two conditions to be obligated in truma. One is the produce reached a third of its growth in the possession of a Jew and the smoothing of the stack was done by a Jew. This is like the law with hekdesh where the Yerushalmi says you need both in maasar chapter 3 and peah chapter 4 and brough in the Rambam in maasar ch2 law 8.the reason I bring all this is to mention that this is the opinion of the Tosphot Gitin page 47a that R Elazar holds you need both the third growth and the smoothing to be in the possession of a Jew. That is because R Elazar holds a gentile has the ability to remove the obligation of truma by means of acquiring the land, and that opinion depends on the fact that you need the third growth to be in the possession of a Jew. Tosphot adds that R Elazar can hold from the fact that you need the smoothing also to be by Jew. So, in the approach of Reb Chaim, Tosphot and the Rambam hold the same opinion.------------------------------------I would like to bring here in short what ר' חיים of בריסק said about this particular רמב’’ם and the argument between the גר''א and the כסף משנה about its meaning. The רמב’’ם himself says if a gentile owns land in ישראל ,then when a Jew buys it back from him, the produce will be obligated in תרומה and מעשר. The כסף משנה says the meaning is that both the land and produce need to be in the possession of the Jew in order to be obligated in תרומה. NOW ר' חיים says the reason for the רמב’’ם and the כסף משנה is that you need two conditions to be obligated in תרומה. One is the produce reached a third of its growth in the possession of a Jew and the smoothing of the stack was done by a Jew. This is like the law with הקדש where the ירושלמי says you need both in מעשר פרק ג and פאה פרק ד and brought in the רמב’’ם in מעשר פרק ב חלכה ח. The reason I bring all this is to mention that this is the opinion of the תוספות גיטין page מ''ז ע''א that ר' אלעזר holds you need both the third growth and the smoothing to be in the possession of a Jew. That is because ר' אלעזר holds a gentile has the ability to remove the obligation of תרומה by means of acquiring the land, and that opinion depends on the fact that you need the third growth to be in the possession of a Jew. תוספות adds that ר' אלעזר can hold from the fact that you need the smoothing also to be by Jew. So, in the approach of ר' חיים, תוספות and the רמב’’ם hold the same opinion.---------------------------Rav Shach however explains the Rambam and Kesef Mishna differently than Reb Chaim. Now the first opinion of the Kesef Mishna is that the Rambam is deciding the law like Rabah that there is no acquisition to a gentile, and with that approach he explains how the Rambam decided that the produce becomes obligated in truma from the Torah only after the property has retuned to the possession of a Jew. But as long as the property is in the possession of the gentile, the produce is not obligated in truma from the Torah. Based on this I can see an amazing thing in the Rambam. For the Rambam says that after the Jew has bought back the land the produce is obligated in truma from the Torah. The Rambam never says anything about reaching a third of its growth. Thus, the Rambam and Kesef Mishna are being consistent here. The implication is that even after the produce has reached a third of its growth in the possession of the gentile, still once the Jew has bought back the land the produce is obligated in truma. This is consistent with the opinion a gentile has no ability to remove the obligation of truma which also holds the third is not relevant. The only thing which makes the produce liable to being truma is after the smoothing of the stack by a Jew.-------------------רב שך however explains the רמב’’ם and כסף משנה differently than ר' חיים. Now the First opinion of the כסף משנה is that the רמב’’ם is deciding the law like רבה that there is no קניין to a gentile and with that approach he explains how the רמב’’ם decided that the produce becomes obligated in תרומה from the תורה only after the property has retuned to the possession of a Jew. But as long as the property is in the possession of the gentile, the produce is not obligated in תרומה from the תורה. Based on this I can see an amazing thing in the רמב’’ם. For the רמב’’ם says that after the Jew has bought back the land the produce is obligated in תרומה from the Torah. The רמב’’ם never says anything about reaching a third of its growth. Thus, the רמב’’ם and כסף משנה are being consistent here. The implication is that even after the produce has reached a third of its growth in the possession of the gentile, still once the Jew has bought back the land, the produce is obligated in תרומה. This is consistent with the opinion a gentile has no ability to remove the obligation of תרומה which also holds the third is not relevant. The only thing which makes the produce liable to being תרומה is after the smoothing of the stack by a Jew.