Making random objects magnetic: no. Magnetizing a metal in the fashion you could also do with a strong magnet: yes! Rotating magnetic fields: he can't make it a persistent property of the object but he can do it very briefly, scattering a bunch of iron filings in a suggestive fashion before it stops quite working. 

(Meritxell points out that if there were a permanent 1/7th decrease in farming productivity all the least productive farmers would starve but there is variance and some farmers are very productive and would be fine.)

"What makes some farmers more productive?  Any clues?"

Can he make a loop of metal superconducting with Prestidigitation, and then use this bit of iron he already magnetized to start an electric current flowing which will then persist?  Keltham has a detailed qualitative-physics mental model of both conductivity and superconductivity if that counts for anything; he wouldn't know exact numbers on how conductive a piece of impure iron would already be.

"Some places the soil is much richer so plants grow better," says Tonia. "And near rivers it's possible to irrigate the fields."

Getting an electric current flowing isn't working and it's not totally clear why.

Fascinating.  If you can make something taste even vaguely like chocolate, you'd think you could make it support a superfluid of phonon-coupled paired electrons; that's much less complicated than the implied fitting-of-taste-receptor-potential-energy-surfaces going on with 'tastes vaguely like chocolate'.

Can he make something just exhibit the magnetic-field-expulsing effect, so that it will float above a magnet even if it's not a superconductor?

(The classic Science Maniac Verrez maneuver would be to see if you can use Prestidigitation to turn a very tiny amount of something into antimatter, but that, obviously, Keltham is not going to talk about, or try until he's got a much better grasp on safety precautions.)

Yep! ...very briefly, again, like with the magnetic field, and then he loses it and has to start again.

Then Keltham is going to practice this some more, because if he gets magnetic field expulsion and magnetism both working, and if he's right about how things look to Detect Magic, he's going to be able to show off an object floating above another object without any visible magical force holding it up, which should make a nice Difficult-Seeming Impressive Trick for Golarion natives if they don't already have any obvious ways for doing that.

Carissa comes quietly in while he's still getting this down (having swung by Maillol's to ask calmly for confirmation that was, again, Her Infernal Majestrix.)

Keltham wasn't at the stage of being ready to attempt a visible Thing Floating Above Thing effect, just bringing Prestidigitated objects closer together to see if he can maintain the repulsive force he's aiming for and especially while he's not actively casting the Prestidigitation spell.  This is good because he doesn't need to hide the preliminary stages of a Difficult-Seeming Impressive Trick from Carissa, who might otherwise be impressed by the completed form.

"Oh, hey," Keltham starts to say when Carissa steps in -

She's dressed nicer and more normally, though not in anything like a dath ilani style.

"Oh, did you get back your non-Worldwound wardrobe and stuff?"  That's a sensible thing for the trip to have been about.

"Yes -- well, acquired a non-Worldwound wardrobe, I haven't had one in mothballs for the last six years. Also acquired some other things I'll tell you about later."

Not bad for a low-tech society.  He'd visualized non-Governance clothing as being much cruder, given the description of hand-powered spinning and weaving - wait is that actually incredibly expensive stuff that only third-circle wizards on important government projects can afford?  He'll quietly ask somebody who isn't Carissa, which he can totally do now, because maaaaaagic.

"I've been practicing economicmagic!" Keltham says.  "Observe what I now do completely without a huge supply network to manufacture sound-transmission equipment."  He goes through the gestures to cast and catch Message, then mouths to Meritxell, "Do her new clothes look very expensive?"

"Yes," Meritxell whispers back, smiling.

Good news about Carissa's career trajectory, not such great news about the state of the rest of Cheliax.

"You also seem more - generally cheerful?  Brighter?  If I'm not just imagining things."  (Said to Carissa normally.)

"You're very perceptive, it is generally said that you need to get multiple prettiness treatments if you want a man to actually notice instead of just vaguely feeling fonder. That is one of the other things I was going to tell you about later."

Keltham peers at her more closely.  "That... could be a change to underlying biology that I interpreted as cheerfulness, I suppose.  If you hadn't told me it wouldn't have occurred to me that your hidden-background-state appearance had changed."  Oh, huh, Keltham has slightly mixed feelings about that, which he should put a pin into discussing sometime later - should he mention it now so she can help him pin it? - no, that seems like an ominous and unspecified thing to dump on somebody if you're not going to talk about it right away.

Keltham casts Detect Magic, just to see if he can spot any lingering magic on or about Carissa from it all.

Nope! 

"Have you eaten yet?  I'm afraid we already did."

“I’ll grab myself something and come right back, then.”

He's about ready to wrap up.  After this comes Keltham's casting his mysterious cleric spells for the day - though Keltham isn't going to mention that fact until she's done eating dinner, in case it's otherwise a nice-mood-spoiler.  (Though she might not actually be in a nice mood, just prettier; still, same logic applies.)

"See you soon and again," he says, in a Baseline idiom that maybe didn't quite translate to Taldane.

She hurries out, smiling.

More magnetic-field-excluding practice!  Also more infinite Additional Questions!

"Is the limitation on irrigating more fields the limited supply of water, or the cost of infrastructure to transport water?  What, if anything, do you already do to try to make fields have richer soil?"

“You leave the fields fallow some years,” says Tonia, “and turn the soil deeper.”

”In some places they harvest bat shit from deep caves and the Underdark.”

Carissa requests a summary over dinner or anything that’s come up, and also wonders aloud at Security whether Asmodia’s been behaving herself better or worse or the same.

Keltham asked questions about farming and other aspects of Chelish economics.  Meritxell and Tonia mostly answered them, in a way that fits the hypothetical new Cheliax so far as Security could tell.

Ione passed a note to Security offering to warn Keltham to maybe not trust everything Meritxell says about economics, because she might be overrunning her real knowledge - in a very enthusiastic and well-intentioned way, but still.  Security is deferring that decision to Sevar.

Ione oracled in one Ostenso library book about farmers - Security does still have the ability to redirect Keltham's thoughts away from text, and farming seemed innocuous.  It didn't contain nearly as much direct detail on farming operations as Keltham had hoped; no illustrations of plows or mentions of how much a plow costs or who makes plows, and soon Keltham gave up and stopped reading.  Keltham suggested establishing communications with somebody at the Ostenso library who could check through books first given a request for content, and leave a found book in a designated place for Ione to borrow.  One Sending is an improvement over two teleports, or this potentially warrants a paired mirror.  Security told him that Requisitions said she'd think about it; Requisitions in this case really means Sevar, they can get the mirrors if Sevar says yes.

Asmodia has been keeping to her bedroom and rereading her math textbooks, which is overtly good behavior.  She wasn't tightly monitored but spot-checking of thoughts suggests that she's anxiously locking down a lot of disloyal thoughts, nothing unusual for someone in her position though of course Asmodia isn't being told that, but certainly more anxiety and thought-suppression than would have been characteristic of her three days ago.  Overt thoughts indicate willingness to work with Sevar on her mysterious project for dath ilani thinking, confusion about what the real purpose of that is, painful hope that maybe she can avoid Hell after all.

Pilar was almost but not quite killed when a Security wizard got a message announcing one of his wives had successfully birthed a child, and Pilar shouted "Congratulations!" from directly behind him.  Nobody including Pilar understands how Pilar got into the temple room where the wizard was receiving the message, and Pilar can't quite remember what she was doing just before that.  Pilar thinks she could possibly learn to not do it to on-duty Security, so long as she can still do it sometimes to somebody, but on this occasion the impulse took her by surprise.  Pilar is significantly shaken up about this, because if she'd died like that she wouldn't have been Maledicted first.  Also, Pilar needs to throw somebody a larger party, preferably a surprise party; single pieces of cake being handed out on special occasions aren't going to cut it for her indefinitely.  This is mostly Maillol's problem but is being copied to Sevar in case it somehow interacts with project matters, or for that matter in case she wants to advise Maillol that having a Chaotic Good oracle to exhibit to Keltham isn't worth that much.

Cayden Cailean is like the kind of god Carissa would have made up if she were a propagandist trying to convince Chelish people that Good is stunningly worthless and stupid. Probably it's fine if Pilar throws some parties, how expensive can that even be, though the only acceptable targets for surprise parties are the other girls and maybe whoever's on staff doing laundry or whatever. Coordination with the library in Ostenso seems straightforwardly good for the cause of passing Keltham only desired books, worth a mirror. If Tonia and Meritxell are the chattiest girls they should both get some training/screening for how to handle it if Keltham wants to fuck them.

Carissa heads back over once she's had enough to eat.