OCTOBEE 22, 1920] 



SCIENCE 



377 



periments have at least two variables, and it 

 would be impossible to ascribe differences in 

 growth to one element with any certainty that 

 the other element was not partly responsible 

 for the result. The recent facts brought out in 

 regard to sulphur should lead at once to a 

 widespread ree^^amination of these problems, 

 with more rigidly designed and controlled ex- 

 perimentation. 



The basic facts brought out are briefly sum- 

 marized here. In the first place, soil studies 

 have shown that sulphur is one of the rare 

 necessary elements. Soils are generally no 

 richer in sulphur than in the fertilizer ele- 

 ments, nitrogen, phosphorus and potassium. 

 This scarcity of sulphur in normal soils is 

 probably related to the ready leaching of sul- 

 phur into drainage water. At the same time 

 improved analytical methods have demon- 

 strated that crop plants require more sulphur 

 than was formerly supposed. They remove it 

 from the soil fully as rapidly as they remove 

 any of the other elements which may become 

 limiting factors. The normal sulphur content 

 of soils is sufficient for from fifteen to seventy 

 crops, provided there are no additions from 

 outside sources, as from rainfall. Even if we 

 count in the rainfall sulphur, it is probable 

 that sulphur is just as often a limiting factor 

 as is phosphorus, or nitrogen, or potassium. 

 For two of the last named elements do not 

 leach as readily as sulphur. The important 

 point is this: If sulphur is a limiting factor, 

 addition of any other fertilizer is useless, and 

 a waste, just as much as would be the use of 

 gypsum as a fertilizer if phosphorus were the 

 limiting factor. 



Instead of thinking of the IST. P. K. formula 

 as representing a " complete " fertilizer it is 

 time we began work solely from the stand- 

 point of limiting factors, including not only 

 these tihree, but S, Ca, Mg, and any other fac- 

 tors which influence crop production. The 

 early failures with gypsum were probably due 

 to the fact that phosphorus or some other ele- 

 ment besides sulphur was limiting growth, or 

 that sulphur at any rate was not the thing 

 needed. These remarks must not be construed 

 as argument for the discontinuance of any of 



the fertilizer elements now in common use. It 

 would be a grave error to try to replace them 

 with sulphur when they are deficient, but we 

 can no longer ignore sulphur as one of the 

 very important fertilizer elements. 



Since the Cruciferse and Leguminosse are 

 known to use quantities of sulphur in their 

 metabolism, crop plants of these families must 

 be the ones most likely to suffer from defi- 

 ciency of sulphur. Recent work by Eeimer'- 

 at the Oregon Agricultural Experiment Sta- 

 tion is very significant and deserves the atten- 

 tion of agriculturists and scientists all over 

 the country. He has found that many of the 

 soils of Oregon are deficient in sulphur, and 

 that addition of sulphur-containing compounds 

 of almost any kind may lead to very remark- 

 able increases in the yield of alfalfa or clovers 

 upon such soils. His experiments extended 

 over several years, and involved a variety ol 

 soils. The increased production ran from 50 

 to 1,000 per cent, in alfalfa, with application 

 of such sulphur-containing materials as gyp- 

 sum, superphosphate, flowers of sulphur, etc. 

 Addition of phosphorus without sulphur had 

 practically no effect, showing that the acid 

 phosphate was valuable only for its sulphur 

 content in this case. The possibility of such 

 increases is a challenge to agriculturists every- 

 where in these times of under production. 



The best results seem to come when the sul- 

 phur is used as a top dressing on the legume 

 crop. The usual custom in the United States 

 is to fertilize the cereals, wheat, etc., and allow 

 the legumes to get the effects a year or two 

 later. Sulphur applied in this way does the 

 legume crop little good, for most of it disap- 

 pears out of the soil by leaching before the 

 legume comes in the rotation. The early suc- 

 cesses were most notable when application of 

 the sulphur fertilizer was made directly to the 

 crops most needing it, the legumes. These 

 convert the sulphur into the organic form, 

 and if used as green or stable manures pro- 

 vide sulphur for succeeding crops in a non- 

 leaching form. It seems quite clear that we 



1 Reimer, F. C, ' ' Sulphur as a Fertilizer for 

 Alfalfa in Southern Oregon, ' ' Oregon Agr. Coll. 

 Exp. Sta. Bull. 163, 1919. 



