CONJUNCTIVE USE OF SALINE AND NONSALINE WATERS .1. RESPONSE OF WHEAT TO INITIAL SALINITY PROFILES AND SALINIZATION PATTERNS

Response of wheat (Triticum aestivum L.) to salinity stress at differe nt growth stages and patterns of salinisation was studied in microlysi meters. The treatments consisted of variable initial salinity profiles (salinity increasing, decreasing and uniform with depth) in combinati on with different salinisation patterns achieved through irrigations w ith waters of increasing, constant, decreasing salinity, alternating s aline and non-saline, introducing saline waters after jointing, keepin g the total salt input through these irrigations the same. Almost 3-fo ld variations in wheat yields were observed. In soil where initial sal inity increased with soil depth, yields were markedly improved (30-36% ) compared with the soils having uniform or inverted salt profiles. Si milarly, shifting to saline irrigation at jointing, cyclically non-sal ine/saline water or increasing salinity, outyielded the others. Intere stingly, lowest yields were obtained in soils receiving constant salin ity waters. Amongst the various indices of salinity, yields were best related (r=-0.78) to root length weighted salinity over different peri ods of growth. Independent estimates of salinity responses showed the tolerance of wheat to increase with ontogeny. The EC50 values (electri cal conductivity of saturation paste extract for 50% yields) increased to 9.3, 10.8 +/- 0.1, 12.7 and 13.2 dS/m for periods between sowing t o crown rooting, crown rooting to boot, boot to dough and dough stage to maturity, respectively. Results imply that for non-steady state con ditions such as those prevailing under monsoonal climate, the salt tol erance at critical stages of crop plants, changes in responses to sali nity with modes of salinisation and initial distribution of salts need to be considered for effective use of multisalinity waters.