Microclimatic profiles in soybean- pearl millet intercropping systems

A field experiment was conducted during kharif season of 2003-2004 at research farm of department of Agril Meteorology, CCS HAU, Hisar located at 29º102 N lat75º462 E. long and 215.2 m above the MSL The experiment comprising eight treatments was laid out in a RBD with three replications. The crop was sown as rain fed in the last week of June. The temperature and relative humidity profiles were measured at four phenophases using Assmann’s psychrometer. Air temperature profiles in all treatments were inverse throughout the day in comparison to the bare field. Relative humidity was higher in the crop canopy than above crop canopy in all the treatments but after harvest of pearl millet, the slope was less than that in the earlier growth phase. Leaf area index, dry biomass accumulation, test weight, yield and harvest index were reported for all the treatments.

Oilseeds form the second largest agricultural commodity after cereals in India, sharing 14 per cent of the country's gross cropped area and accounting for nearly 5 per cent of the gross national product and 10 per cent of value of agricultural products. India ranks fifth in the world in soybean production (50.9 lakh tones), however productivity in India (1008 kg ha -1 ) is one of the lowest compared to 2140 kg ha -1 in the world (Hegde2000). The microclimate of the crop is primarily determined by the manner in which radiant energy is portioned into different fluxes. Microclimatic profiles in soybean sole and intercropped with pearl millet under different planting systems are reported.
Dry and wet bulb temperatures were measured at different phenophases from 0800 to 1600 hours at ground, 50, 100, and 200 cm height using hand held clock spring type Assmann's psychrometer. The relative humidity was calculated using psychrometeric table. The temperature and relative humidity profiles were drawn for four phenological stages of the crop to reflect the crop microclimate.
Three randomly selected plants from each plot were cut from the surface and leaves were removed for recording leaf area by leaf area meter (LICOR 3000) and leaf area index was calculated. The same plants along with pods were also used for dry matter observation. Sun dried samples were dried in oven at 70 0 C temperature till constant weight was attained and expressed as mean dry weight (g plant -1 ). The plants per square meter, pods per plant, seed per pod, grain yield (kg ha --1 ), test weight of soybean (100 seeds) and Pearl millet (1000 seeds) were recorded at the time of harvest.

Temperature profiles
The microclimate of crop stands was largely influenced by air temperature within and above the canopy temperature profiles were drawn at four phenophases depicted in figure 1 to 4 (upper). At all phases the profiles indicated that temperature inside the canopy was lower than that above the canopy in all the treatments (i.e. temperature profiles showed an inversion throughout the day) But slope of the air temperature profiles was greater at vegetative stage than that of later growth phase of crops. There was no notable difference found in temperature profiles of different treatments. Hence only temperature profiles of T 1 , T 2 , T 4 and bare field are shown here.
The temperature variation from bottom to top of canopy could have resulted partly because of the transpirational cooling occurring inside the canopy and partly because of the reduced transmission of solar radiation to the bottom of the canopy. Similar results were reported by Niwas (1986) for brassica, Baldocchi et al. (1983) for soybean and Shivdeva (1986) for Gram + Raya intercropping.

Relative humidity profiles
Relative humidity was higher in the crop canopy than above it in all the treatments throughout the crop duration but after the harvesting of pearl millet, the slope is less than those in the earlier growth phase, figure 1, 2, 3 and 4(lower). Relative humidity profiles were lapse inside the crop canopy throughout the day but profiles were nearly isohumic at 0800 hrs and 1600 hours in most of the treatments. The relative humidity under crop field was higher than that above Table 1: Effect of sole and intercropping systems on leaf area index (LAI), accumulated dry matter (g plant -1 ), grain yield (kg ha -1 ), test weight and harvest index the bare soil by 10 to 20 per cent. These results are in close agreement with the results of Shrinivas (1984) for rice. Niwas (1986) also reported the same result for brassica.

Growth and yield
Maximum leaf area index accumulated dry matter, grain yield, test weight and harvest indices of both soybean and pearl millet for all treatments are depicted in Table 1.Soybean recorded significantly higher (LAI) accumulated dry matter in the case of T 4 while test weight and harvest index showed non significant difference among the various treatments. Pearl millet produced significantly higher LAI and accumulated dry matter in T 6 (soybean + pearl millet, 4:1) whereas T 2 recorded significantly highest yield over all other treatments. Harvest index of Pearl millet was significantly lower in T 2 . the significant higher LAI and dry matter for pearl millet in T 6 was partly due to low plant density as soybean: Pearl millet ratio was 4:1. Joshi et al (1999) reported that planting of soybean and pigeonpea in alternate paired rows (30 cm) gave highest land equivalent ratio (1.69) due to minimum competition between crops. soybean in T 4 was due to lower intra species competition, availability of more space and better utilization of natural resources than other treatments. Pearl millet produced significantly higher LAI and accumulated dry matter in T 6 (soybean + pearl millet, 4:1) whereas T 2 recorded significantly highest yield over all other treatments. Harvest index of Pearl millet was significantly lowest inT 2 whereas test weight showed non significant difference among various treatments. The significant higher LAI and dry matter for pearl millet in T 6 was due to low plant density as soybean: Pearl millet ratio was 4:1 and also due to lower competition with short stature and slow growing nature of soybean Joshi et al (1999) again revealed that planting of soybean and pigeon pea in alternate paired rows (30 cm) gave highest land equivalent ratio (1.69) due to minimum competition between crops.