Let’s go through definitions of a few terms in your question to make sure we’re on the same page. First, it’s important to actually set out the definition of “arable land” and how that affects land management, property regimes, and colonial policies in the British Mandate era. Today the FAO (Food and Agriculture Organization) of the UN defines “arable land” as: “land under temporary crops…temporary meadows for mowing or pasture, land under market and kitchen gardens and land temporarily fallow (less than five years). The abandoned land resulting from shifting cultivation is not included in this category.” By “temporary crops” we mean annuals—cereals, row crops, fresh vegetables, etc. Essentially anything you have to plow over and plant every year. Perennials are not included in the ‘arable’ category because they don’t turn over. Most fruit are perennials, whether as trees (olives, citrus, apples, whatever) or shrubs and vines (for Palestine, historically grapes is really the only thing in this category; berries are historically not an important crop in the area). Nor does “arable land” include pastures, which despite mainstream ideas that they are simply “empty land,” actually require management, stewardship, and cultivation just like planted crops (see Nathan Sayre’s work on North American rangelands for more). The linked FAO doc notes that these important types of land are not considered “arable land” and this is very relevant for historic Palestine as permanent orchards and animal husbandry through grazing are some of the most economically and culturally significant forms of agriculture for Palestinian Arabs.

Towards the middle of the Mandate period, 1930, here’s the stats for agricultural production in Mandate Palestine: “Forty-five per cent of the farmers cultivated cereals (wheat, barley); five per cent produced special crops (for example, vegetables), three per cent were in animal husbandry and forestry; and 0.1 per cent grew citrus. Eighty-one per cent of the cultivated land was arable, 14.6 percent orchard, 2.1 per cent forests, 1.2 per cent pasture, and 1.1 per cent productive wasteland.” (El-Eini 2006, 120-121) So we can see that numerically most farmers are producing annual crops. Yet economically “74 percent of exports” are citrus fruits; 90% of Mandatory Palestine’s exports overall are agricultural products. So citrus plantations were a hugely economically significant portion of Palestine’s agricultural production even though we can see only 0.1% of farmers are growing it. Already you can see that must mean that citrus cultivation is concentrated in the hands of very few large landowners.

This wasn’t always the case; while citrus cultivation has been grown in Palestine since antiquity, the advent of steam ships that allowed the fruit to quickly reach markets in the Mediterranean and Europe before spoiling led to a major expansion of area put to citrus orchards use around the turn of the century. Jewish and Arab landowners alike got involved with the expansion of citriculture in the end of the 19th and early 20th century before the Mandate. While Karlinsky acknowledges that “Jewish citrus holdings were exceedingly small in the 1890s,” he notes this begins to change with the Rothschild moshavot and that “citriculture was from the very start a markedly capitalistic industry, developed by private entrepreneurs” (unlike more cooperative efforts for other crops) (Karlinsky 2005, 52). Karlinsky pulls multiple sources together to find that in Rishon LeTzion, one of the biggest citriculture areas for Jewish farmers, by the 1920s “More than 40 per cent of the growers were “absentee landlords.”” (60) Many of these landlords did actually live in Palestine but in cities and were not actively involved in farm labor or management. Arab citriculture started off as taking up significantly more land than Jewish citriculture at the beginning of the Mandate period; then Jewish “planting frenzy” grew in the 20s and 30s as profit margins rose, and then it plateaued right around the Arab Revolt of 1936 due to a price ceiling and capital limitations. However while we mostly think of Arab citriculture as big plantations, Karlinsky notes that “according to estimate [sp] made by Charles Kamen, large estate owners held only between 25 and 45 percent of the land on the coastal plain, where most citrus planting (Jewish and Arab) took place. Consequently, not only “deep pockets” but also small Arab landholders could venture into citriculture there.” (156) So to summarize, in general one would say that the majority of both Jewish and Arab citriculture land was controlled by large landowners, but by no means all of it.

This however doesn’t answer your technical question about “arable land” – I go into citriculture because I assumed you meant a more colloquial definition of “arable” as “land able to be cultivated for any purpose.” If we take the strict definition above, we can get into more detail – honestly more detail than I can maybe handle in this post which is already thousands of words long ;) I would direct you to Roza El-Eini’s book, she has a chart on p. 122 that shows by district (coastal plain; inland plains; Jordan Valley; central hills; and Naqab desert) which compares total land cultivated with and without irrigation against “total cultivatable land” in the Mandate era. In the rich coastal plains you have a fairly high rate of cultivation (2.25 million cultivated out of 2.72 million total) vs in the Naqab it’s listed as “several million” possible to cultivate.

The issue is here though that cultivation is as much a political and economic designation as it is a technoscientific one. The British colonial project in Mandatory Palestine was greatly concerned with the question of developing and “improving” the land, as was the Zionist project. Thus the British might see, for instance, seasonal pastures in the Naqab used by nomadic Bedouin pastoralists who migrated through different regions year to year as “potentially cultivatable” but not actually cultivated as there was no planting or harvest that was recognizable to them. The British spent a lot of time trying to restrict traditional grazing, blaming it for everything from deforestation to desertification, even though it was a huge part of land use and important economic and cultural practices for Arabs. Tamar Novick doesn’t put a number on it but in quoting a British source about restricting grazing, she notes the veterinary officer says that there are “large areas of the land [of Palestine] which is at present utilized for grazing of the stock.”” (Novick 163).

Additionally large Arab landowners (either mukhtars or village chiefs, or effendis local elites) could often lay legal claim to more lands than they technically owned and definitely more than they actively cultivated. I have spoken about the Ottoman Land Law of 1858 in previous answers and how the threat of taxation and conscription led many fellahin (Palestinian Arab peasantry) to let notables register the land in their name to avoid these issues. Those were the “absentee landlords” who are usually referred to who sold large tracts of land to Jewish Zionist settlers in the Mandate period. Additionally, while a lot of scholarship focuses mostly on the peasantry as the drivers of Palestinian nationalism, new work is coming out looking at how the Palestinian middle and owning classes participated in national projects including by trying to collaborate with the British – and how anticolonial sentiment grew when they were excluded from modernization efforts. El-Eini describes how the agricultural loan system set up by the British to build out irrigation systems tended to inadvertently favor Jewish development due to the community institutions they had set up; Arab economic cooperatives and community banks were soon set up but lagged behind. Jacob Norris also describes (more on extraction of natural resources and less on agriculture) how the British colonial project “in the eyes of Palestinians was tainted as much by their exclusion from projects of modernization as it was by opposition to Jewish immigration or the dispossession of the fellahin” (2015, 275).

Strangely enough in looking deeply into a lot of sources on this question I still can’t find a good definition of “large landowner” – so much of this literature refers to the absentee Arab landowners but they don’t really put a number of dunams on how much “large” means. Here for instance is a summary of the post-White Paper of 1930 report by Louis French, British Director of Development, on Arab landholdings: French found that “Arab capitalists had acquired over 30 per cent of the land in one unnamed subdistrict over the course of just the preceding decade. No less remarkably his report also estimated that half of all Arab cultivators on the land were sharecroppers, not landowners.” (Anderson 2018, 186) But this still doesn’t put a number on how many dunams one had to own to be considered a “large landowner.”

(continued in another reply due to character limit)