AfriForum is frankly an unreliable source and pushes a white nationalist agenda.  You shouldn't even be regarding claims they make as worthy of hearing out.  
<blockquote>AfriForum's claim to be a civil rights organisation has been questioned in the South African media, and South African and international media often characterize Afriforum as a white nationalist or white supremacist group.</blockquote>  
https://en.wikipedia.org/wiki/AfriForum  

Fact-checkers have widely identified the notion of a "white genocide" in South Africa as a falsehood or myth.  
<blockquote>The tweet gives prominence to a false narrative pushed by some right-wing groups in South Africa that there have been numerous seizures of white-owned land and widespread killings of white farmers. Some of those groups have brought their claims to the United States on lobbying trips.</blockquote>  
<blockquote>The number of killings of farmers, including farm workers, is at a 20-year low, 47 in the fiscal year 2017-18, according to research published in July by AgriSA, a farmers’ organization in South Africa. That is down from 66 during the fiscal year before. The figures were consistent with a steady decline of violence since a peak in 1998, when 153 were killed.</blockquote>  
<blockquote>South Africa recorded 19,016 murder cases from April 2016 to March 2017, according to the South Africa Police Service. The national murder rate last year was 34.1 per 100,000 people, but the number of people living on farms is not fully known, which makes comparisons difficult.</blockquote>  
Math: this means that farmers of all races combined only account of 0.35% of all murder victims in South Africa, because 100 * 66 / 19016.  South Africa currently has no crime statistic breakdown by both race and farmer status; which casts further doubt on anyone claiming that they possess reliable stats supporting a white farmer genocide.
<blockquote>Does the South African government want to seize land?

Yes.

Mr. Ramaphosa announced on Aug. 1 that the governing African National Congress (A.N.C.) would move ahead with a proposal to change the country’s Constitution and allow the expropriation of some land without compensation.

Land reform is a highly divisive issue in South Africa, where whites own disproportionately more private land than the black majority in both urban and rural areas.</blockquote>  
https://www.nytimes.com/2018/08/23/world/africa/trump-south-africa-white-farmers.html  
https://www.washingtonpost.com/politics/2018/08/24/president-trumps-false-claim-about-murders-south-african-farms/?noredirect=on&utm_term=.9ea432f95d98  
https://www.theguardian.com/world/2018/jun/27/murders-of-farmers-in-south-africa-at-20-year-low-research-shows