The lime (Ca) induced iron (Fe) chlorosis, commonly known, as Fe-chlorosis is of common occurrence in groundnut crop in calcareous soils worldwide. In India more than one-third of the soil is calcareous and spread mostly in low rainfall areas where groundnut is a major oilseed crop. Fe deficiency chlorosis (FeDC) as an interveinal to complete chlorosis in young and emerging groundnut leaves, which depending upon the intensity of chlorosis, may result in death of plant causing little yield losses to complete crop failure. Soil application of iron sulphate (FeSO4) to prevent FeDC and foliar application of Fe containing soluble salts to ameliorate Fe deficiency in standing crop are presently being recommended to increase and sustain the productivity in calcareous soils under rainfed and irrigated farming situations. However, the soil application requires large amounts of Fe-fertilizers, whereas, foliar application requires frequent applications and these practices may not be viable solutions on long-term basis. Under such circumstances, use of genotypes, which can overcome the Fe-deficiency chlorosis by efficient utilization of native Fe, could be the potential alternative solution to this malady. Further, genotypic differences exist in groundnut with respect to their performance in calcareous soil. The evaluation of indigenous and exotic groundnut germplasm collection over several years at National Research Centre for Groundnut (ICAR), Junagadh (India) lead to the identification of Fe-efficient genotypes in India. With this background, a field experiment to study the productivity potential of Fe-efficient groundnut genotypes (FeESG 8 and FeESG 10) and their response to the soil and foliar application of iron sulphate was conducted in calcareous Vertisols at Amminabhavi village, Dharwad District, Karnataka State (India) during rainy season of 2000 under assured rainfed farming situations. The rainfall received during the crop growth period was 396.0 mm. The initial soil tests values were 8.5 pH, 0.62 dS/m EC, 0.62 % organic carbon, 21.0 % free CaCO3, 265 kg available N/ha, 7.15 kg available P2O5/ha, 610 kg available K2O/ha, 21.7 kg available S, 3.89 ppm Fe (DTPA extractable) and 0.59 ppm Zn (DTPA extractable). The experiment consisted of five main plots (groundnut genotypes) (TMV 2, Dh 53, JL 24, FeESG 8 and FeESG 10) and three sub-plots (Fe-management practices) (No Fe application, soil application of FeSO4 @ 25 kg/ha and foliar application of FeSO4 @ 0.50 % at 30,45 and 60 days after sowing). The experiment was laid out in Split Plot Design with three replications. A common dose of fertilizers consisted of 25 kg N, 75 kg P2O5 and 25 kg K2O/ha along with FeSO4 as per the sub-plot treatments were applied at the time of sowing. Seeds of groundnut cultivars were hand dibbled at a planting geometry of 30 cm x 10 cm. Crop was kept weed free and disease and insect free by integrated plant protection measures.
The results indicated that the Fe-efficient genotypes FeESG 8 and FeESG 10 (Spanish bunch types with maturity duration of 95 to 100 days) showed good yield potential in calcareous soils with high amount of free CaCO3 (21.0 %) compared to traditional groundnut genotypes (TMV 2 and JL 24). Without any Fe-management practices (either soil or foliar application of FeSO4), genotypes FeESG 8 and FeESG 10 produced higher dry pod (1460 and 1580 kg/ha, respectively) and kernel yield (987 and 928 kg/ha, respectively) compared to genotypes TMV 2 (671 and 444 dry pod and kernel yield/ha, respectively), JL 24 (731 and 474 kg dry pod and kernel yield/ha, respectively) and Dh 53 (671 and 444 kg dry pod and kernel yield/ha, respectively). Further, Fe-efficient genotypes FeESG 8 and FeESG 10 showed lower per cent of chlorosis at different growth stages. The per cent chlorosis observed in FeESG 8 and FeESG 10 was ranged between 43.81 at 30 DAS to 23.37 at 75 DAS; and 43.45 at 30 DAS to 21.18 at 75 DAS, respectively. While in Fe-inefficient genotypes (TMV 2, Dh 53 and JL 24), earlier identified as Fe-efficient genotypes, the per cent chlorosis was greater and was ranged from 58.00 to 62.24 at 30 DAS and from 32.02 to 32.76 at 75 DAS.
With regard to Fe-management practices, traditional groundnut genotypes (TMV 2, Dh 53 and JL 24) showed greater response to either soil or foliar application FeSO4 compared to Fe-efficient genotypes (FeESG 8 and FeESG 10). The extent of reduction in per cent chlorosis in groundnut genotypes was greater with foliar application than with soil application of FeSO4.
From the present studies it may be concluded that, for higher and sustainable productivity in soils showing Fe-deficiency symptoms due higher amount of free CaCO3 content, cultivation of Fe-efficient groundnut genotypes such as FeESG 8 and FeESG 10 would be beneficial than cultivation of traditional Fe-inefficient genotype such as TMV 2 and JL 24.