Diagnosing sulfur deficiency in rice by grain analysis

The effect of varying the sulfur (S) and nitrogen (N) supply on theyield and composition of brown rice (Oryza sativa L.)grainwas studied to determine whether grain analysis could be used for the diagnosisof S deficiency in this crop. Plants were grown to maturity in an S deficientyellow podzolic soil, under flooded and upland conditions in a glasshouse. Inthe first experiment there were six application rates of S combined with threeapplication rates of N. The amount of grain per plant varied from 0.69 to 7.62g, depending on the level of S and N supplied. Rice grown underflooded conditions produced approximately twice the grain yield of upland ricegrown at field capacity. Grain from the flooded series generally had a lower Sconcentration, and apart from the grain from the low N treatment, had lower Nconcentrations than the grain from the upland series. The grain S concentrationvaried from 0.069% to 0.154% and the N concentration ranged from 1.06% to 2.14%with changing S and N supply. Strong positive relationships were obtainedbetween grain yield and grain S concentration, and negative relationshipsbetween grain yield and the N:S ratios in the grain. The critical Sconcentration determined for 90% maximum yield in plants well supplied with Nwas not sufficient to distinguish between S responsive and unresponsive plantswhen N was limiting; both grain S concentration and N:S ratio are necessary todetermine the S status of the rice crop. Deficiency was indicated when the Scontent of the grain was less than 0.1% and the N:S ratio was wider than 14:1,and the same criteria applied to rice grain from flooded and upland treatments.Note that these values were derived in a glasshouse experiment using one ricecultivar on one soil and are therefore preliminary and require confirmationbefore practical application in the field. The second experiment examined theeffect of supplemental S applied after anthesis on grain composition. Latesupplemental S had no effect on grain yield, or on the composition of grainfromplants adequately supplied with S. In marked contrast, S concentration in grainof previously S deficient plants increased from 0.08% to 0.2%, well above thehighest level achieved by applying S at sowing. It is concluded that grainanalysis can be used to diagnose retrospectively S status for yield, provided Ssupply does not increase between the stage when grain yields are beingdetermined and the subsequent grain filling stage. An increase in S supplybetween these two stages will change the relationship between grain Scomposition and yield and complicate interpretation of grain analysis fordiagnosis. The advantages of using grain analysis for retrospective diagnosisofS deficiency are discussed, and the preliminary results suggest that theconcepts warrant further testing in the field.