Is it just the rain where it is already wet in North America, and dryness where it is already dry across the world, which is worrying investors?
"We are now in a full blown weather market after the three-day holiday weekend," Benson Quinn Commodities said.
Or is there more to the continued rally in grains?
"This is primarily a weather market, but there is some macro commodity buying that is taking place today also, which is also supporting the grains," Darrell Holaday at Country Futures said.
Certainly, funds bought an estimated 13,000 corn contracts on the day, with 4,000 each in soybeans and wheat. And regulatory data out late on Friday showed speculators raising their net long position in corn futures and options by 15,620 contracts to 313,680 in the weekto April 19.
But there is, as ever, a China angle too, after the country over the weekend was reported as saying that some $2 trillion of its $3 trillion in dollar cash reserves.
"This means that China is going to sell dollars and exchange them for other hard natural resources like metals, enery and grains," Darren Dohme at Powerline Group said.
"When China starts to sell those dollars and buy natural resources with that money, it can very likely cause hyper-inflation."
Precious metals markets were taking the threat seriously anyway, sending gold to a fresh record and pushing silver up 8% at one point, before it retreated back to stand 3% up on the day.
And it was all grist to the agricultural commodities mill too.
That fund buying helped Chicago
"The onslaught of rain in much of the Midwest over the last three days prompted some panic buying as the fields in Missouri, Illinois, Indiana and Ohio are extremely wet, and there will not be any planting for awhile and the forecast remains wet most of week and into the weekend," Mr Holaday said.
American corn sowings are expected in a US Department of Agriculture report due later to be shown 9-12% complete, compared with 45% last year and an average of 20%.
US Commodities said: "The trade will be concerned that trend yields will not be achieved if 40% of the crop is not planted by May 1," with May 10 the date at which yield losses are factored in.
"Some rain did fall in Kansas and Nebraska over the weekend. The dryness in the southern Plains is shrinking."
Still, the USDA crop progress report is expected to see further deterioration in the crop, besides slow progress in spring wheat sowings too, echoing the slow progress already noted in Russia, where seedings are 40% behind last year's pace.
"Temperatures across the northern plains and Canada are raising concerns about spring wheat plantings with little planting progress taking place over the past week," Benson Quinn said.
Chicago wheat for May added 3.3% to $8.26 a bushel, the best finish for a spot contract for two months, while the July lot gained 3.2% to $8.61 ¼ a bushel.
Among soft commodities,
But other softs were not so lucky, lacking the support of China buy talk.
"We have already imported quite a volume to replenish reserves, far more than needed to cover the deficit in producing areas, and also enough to ensure the supply for the current year," he said.
That helped dampen any relief at Indonesia confirming it will import 226,000 tonnes of raw sugar between May and the end of 2011.
New York's May lot added 1.6% to 25.07 cents a pound, while the July lot shed 1.7% to 23.40 cents a pound.
The May lot shed 1.2% to 287.90 cents a pound, with the July lot easing 1.3% to 289.85 cents a pound.