Abstract
In Bangladesh, chickpea is normally grown after rainy season rice and thus faces terminal moisture stress. However the extent to which chickpea is limited by phosphorus (P) deficiency in the different soil types of the country is not clear. The chickpea root system, with a capacity of deep rooting, plays a major role in acquisition of both water and P, and genotypic differences in rooting behavior of chickpea have been recorded. In this study, chickpea genotypes with different root characteristics were compared for their ability to acquire water and P under different environmental conditions.
Four experiments were conducted during 1998-2000, to study the influence of phosphorus fertilizer and soil moisture on the root system, growth dynamics, yield, and nitrogen and phosphorus uptake of several chickpea genotypes.
The first experiment was conducted at ICRISAT, Patancheru, India during October to January, 1998-99. The objectives of the study were to evaluate genotypic variability in chickpea in respect of root traits as well as shoot growth and nutrient uptake (N and P) as affected by different P levels over time. Plants were grown in tall (>1m) cylinders of Vertisol soil and harvested at three growth stages. The plants needed higher P rates (60 kg P ha1) for maximum root growth at the vegetative stage, but only 20 kg P ha1 at the pod-filling stage. ICC 4958 and ICCV 94916-4 produced more roots at earlier growth stages, but at pod-filling stage Annigeri and ICCV 10 were at par with the former two cultivars, and only ICC 5680 had an inferior root system. In general, N and P uptake were improved by P application. At low P application rates, there was a positive correlation between P uptake and root length or mass. The initial prolific rooting capability of the genotypes ICC 4958 and ICCV 94916-4, which also take up more P, could be exploited for developing chickpea genotypes with superior drought escape and P acquisition capability.
The second experiment was conducted during November to February, 1998-99 in a Vertisol field at ICRISAT, Patancheru, India, with a view to investigate the genotypic variability of chickpea root growth under different soil moisture regimes, and to examine the moisture extracting capacity of the cultivars. From this experiment it was observed that irrigation promoted more root growth in upper soil layers (0-15 cm) in both ICC 4958 and ICCV 10. The root length density (RLD) of ICC 4958 was greater than that of ICCV 10, with the zone of greater RLD following the receding soil moisture front in the non- irrigated treatment. Minirhizotron observation showed that maximum RLD was attained at the pod-filling stage, and also confirmed that ICC 4958 possessed higher RLD over time in comparison to ICCV 10. The minirhizotron results could simulate results obtained from root extraction by the monolith method, suggesting that the minirhizotron could be used in studies of root dynamics to alleviate the need for cumbersome, costly root excavations. Frequent irrigation increased grain yield in all the three genotypes by 57-76 % over nonirrigated chickpea, due to the high evaporative demand of the location. Higher yield and harvest index (HI) were obtained from Annigeri compared to the other genotypes. Soil moisture extraction pattern of different genotypes was relatively similar, despite differences in response to irrigation.
The third experiment was conducted during November to March, 1998-99, in the High Barind Tract (HBT) in north-western Bangladesh. The objective of the study was to quantify the influence of applied P and irrigation on root system development, growth dynamics of aerial parts, nutrient uptake (N and P) and yield of chickpea genotypes. Application of 30 kg P ha1 promoted RLD and total root length. In most of the soil layers ICC 4958 had superior RLD over ICCV 10. Soil moisture went below wilting point at flowering to pod-filling stages (late December to February), which was the rapid growth phase of the crop, where maximum water and nutrients are needed. Only a marginal response to the light irrigation was recorded. Among the genotypes Annigeri produced the highest seed yield and HI. Phosphorus application increased the HI. At pod filling stage, roots were found down to 90 cm depth. Average N and P uptake by chickpea plants were around 35 kg N ha1 and 3 kg P ha1.
The fourth experiment was carried out during November to March, 1999-2000, in the HBT of Bangladesh .The experiment was designed to further quantify and confirm the effect of P fertilizer and irrigation on the root system development, growth dynamics of aerial parts, nutrient uptake (N and P) and yield of chickpea genotype Annigeri. From this experiment it was evident that for nonirrigated chickpea applied P is more important for root proliferation compared to irrigated chickpea. Irrigation markedly promoted root growth in upper soil layers (0-15 cm depth). Root dry weight decreased exponentially with depth irrespective of soil moisture regime. Roots were found down to 105 cm depth at the pod-filling stage. Chickpea RLD was less in the HBT than at ICRISAT due to high bulk density of the soil. Optimum soil moisture minimizes the effect of applied P, as soil moisture facilitated the availability of soil-P to plants.