As subdivisions go, the plan for Flat Point Farm in West Tisbury could hardly be more carefully balanced between the need to plan for family succession and the desire to maintain the farming tradition, so threatened on Martha’s Vineyard.

Yet it has served to raise a whole raft of questions that go to the very heart of the Island farming methods, which contribute disproportionately to the Vineyard’s most pressing environmental problem, pollution of the great ponds by excessive nitrogen.

And the answers to those questions could involve new restrictions on the way agriculture is practiced on the Island. Or, alternatively, they could result in a greater burden being placed on everyone else so farms may continue to pollute.

The issue arose when the Fischer family, who have owned Flat Point Farm for generations, brought their succession plan before the Martha’s Vineyard Commission (MVC) recently.

They proposed to put almost 68 acres of the roughly 92-acre property into two conservation parcels. The rest would be split into five four-acre lots — specifically sized so guest houses would not be allowed — around existing buildings. And there would be three youth lots of just over an acre each, reserved for future distribution to family members, in accordance with West Tisbury zoning provisions.

The town planning board had smiled on the plan, but the plan for the farm, located on the Tisbury Great Pond also must be approved by the MVC. Despite some concerns about potential increased road traffic raised by abutters at a recent public hearing, the plan appeared to raise no major red flags there either.

Except, that is, for the question of the use of nitrogen fertilizer. According to the calculations of the MVC water resource planner Bill Wilcox, the farm contributes roughly 2.5 times as much nitrogen to the Tisbury Great Pond as would otherwise be allowed under the commission’s 2007 water quality policy.

That policy set out to regulate development proposals as to the amount of nitrogen they could put into the pond. The regulations were aimed mainly at residential and commercial subdivisions, the most significant source of nitrogen being septic systems.

One thing the policy did not address — because of the considerable complexities involved — was how the commission should deal with agricultural operations. Now, the commission will be forced to address that omission.

And with more farm subdivisions coming up — one for Morning Glory Farm is already on the horizon — it presents a knotty problem.

The benefit of nitrogen is also the problem with nitrogen: it encourages plant growth. It’s a good thing for a field of hay or corn, but a menace in a Great Pond. There, it encourages the growth of algae, which can choke out other life, like eelgrass and shellfish.

Most of the Island’s ponds already are at or over their limit, which is why, two years ago, the commission came up with its policy, based on some complex science and a pretty simple formula.

“Each of our ponds has a nitrogen limit; we have a pretty good idea of what that is,” said Mr. Wilcox.

“So we allocate a proportion of that amount to each acre of land within the watershed of each pond. In the case of the Tisbury Great Pond, the limit for nitrogen is 0.8 kilograms per acre,” said Mr. Wilcox.

“Flat Point is a little over 90 acres, so their allocation under that formula is about 73 kilograms.

“But their actual nitrogen loading number, from my calculations, is 124 kilograms from the farming operations, and another 36.8 from the four houses there. The four proposed houses would bring the total to 198 kilograms.

“So they’re over the loading limit by almost a factor of 2.5.”

That is not to suggest the Fischers are being excessive in their use of fertilizer. Quite the reverse. The agronomic rates — that is the amount of nitrogen recommended to optimize yields for the crops they now grow and the livestock they now run — is far higher, about 269 kilograms.

The Fischers’ operation is very low nitrogen compared with some other farms, Mr. Wilcox said, because they grow mostly pasture crops — hay and alfalfa — which need relatively small amounts of nitrogen, compared with row crops, like corn, for example.

And that fact — that different farms grow different things requiring different quantities of fertilizer — greatly complicates the problem. Suppose, for a minute that it was decided Flat Point Farm were allowed to continue operating as it is now.

That is essentially what Bill Wilcox offered as a possible approach at the MVC hearing.

“What we were suggesting . . . was that we thought the best way to address farms is to determine what the agronomic recommended nitrogen application rates are for the crops currently grown on the farm and to use that as the limit for the agriculture operation,” he said.

“It might exceed our guidelines for the pond, but if it meets good farming practices, we suggested that should be acceptable. While they may impact water quality to an extent, they have other offsetting values.”

But what, then, if the Fischers decided, sometime in the future, they wanted to grow corn, for example, which requires a great deal more nitrogen fertilizer, instead of pasture crops? They would be prohibited from doing so.

“That,” said Mr. Wilcox, frankly, “is a potential worry with the way the policy is set up. We may be limiting their ability to compete with other farms by saying their entire operation is limited to legume hay, for example, because that’s what’s there now.”

Such a grandfathering restriction might even have the perverse effect of encouraging farmers to use more nitrogen. If they knew they were coming up before the MVC, and likely to be restricted to current crops or fertilization rates, they could change crops or increase fertilizer use in order to have that more generous regime grandfathered into a decision.

And there is a further complication. The current water policy applies to proposals which trigger development of regional impact scrutiny by the commission. Flat Point Farm came up solely because of the Fischer family’s succession plan. Would it be fair to limit their use of their land while other farms, not up for MVC scrutiny, continue business as usual?

For, said Mr. Wilcox, every other farm on the Island is in a broadly similar situation.

“They just have not yet come up as a DRI. Morning Glory is on the horizon. That one raises another issue: they own multiple parcels in the Edgartown Great Pond watershed, but they’re only coming in for one of them, which is the one where the farm stand is.

“So the question becomes, what do we look at? Do we look just at that one parcel, or at the whole farm? Plus they grow a lot of corn, which is a very nitrogen-hungry crop.

“I don’t have an answer for that one either. It’s a very tough issue.”

And all the tougher because the Fischers have tried to do the right and prudent thing.

“It’s such a low-density development and they’re restricting development so it will remain farmland probably forever. It’s a pretty wonderful plan in its intent,” he said.

The Flat Point Farm plan is set to come before the commission land use planning committee on Nov. 9, and before the full commission on Nov. 19 for deliberation and decision.

But at least one commissioner, Doug Sederholm, would like to defer the matter until the MVC can come up with further guidelines on farmers’ use of nitrogen fertilizer.

“I would feel more comfortable if we had at least an interim guideline in place that addressed it, that the commission, through a committee and then through the full commission, considered the issue and balanced the values and interests at stake,” he said this week.

“It just so happens that farms very rarely come up in the context of a DRI,” Mr. Sederholm said. “But Flat Point Farm has raised an issue we should address.

“The commission as a general policy wants to promote the continuation of family farms. And given the estate laws, the state tax situation and the land prices on Martha’s Vineyard, people like the Fischers are faced with a true dilemma.

“So to the extent we can accommodate what they have to do to hold onto their farm and meet their tax obligations, to the extent that will promote the continuation of a multi-generation farm I think that is consistent with the values the commission was set up to protect.”

So, what to do? Mr. Sederholm said he yet had no firm opinions.

“All I was doing [when he questioned the lack of policy at the MVC meeting earlier this month] was identifying the issue and saying we should address it.”

But he speculated on an alternative to holding farms to the same levels of nitrogen as everyone else.

“We may give farms, place farms in a different category than one places housing development. We could say agriculture arguably deserves special deference, because we want to preserve it as part of our way of life and history, and because people are now aware of the need to eat locally.

“It’s possible we will have to adjust our nitrogen consumption elsewhere to accommodate the need for nitrogen agriculturally,” Mr. Sederholm said.

And that would open a whole other can of worms. For nitrogen loading of the ponds is a zero sum game. If farmers are allowed more, it means others will be allowed less.

And that can mean only a couple of things. More sewering or more use of nitrogen-reducing septic systems. And either of those would place significant additional costs on non-farmers.