Studies on planting pattern and phosphate fertilization of sole and mixed stands of pigeonpea

ANCHA SRINIVASAN AND l.P.S. AHLAWAT

Division of Agronomy, Indian Agricultural Research Institute, New Delhi-110 012

A modification in the planting geometry of the base crop with recommended plant population would make intercropping more feasible and often remunerative (De et al., 1978). Very few attempts have been made to find out the requirements of fertilizers especially phosphorus in intercropping systems involving short duration pigeonpea (Cajanus cajan (L.) Millsp.) and various intercrops. A field experiment was, therefore, conducted at the Indian Agricultural Research Institute, New Delhi in 1982 to study the effect of planting geometry and phosphate fertilization in sole and intercropped pigeonpea. The soil was sandy loam of 8.l pH containing 0.04% total N, 9.8 kg/ha available P and 166.7 kg/ha available K. Treatments comprised two planting patterns (uniform rows at 60 cm and paired rows at 30/90 cm) and three intercropping systems (sole pigeonpea, pigeonpea + green gram and pigeonpea + sorghum) as main plots and four rates of phosphorus (0, 30, 60 and 90 kg P2O5/ha) as sub-plots replicated thrice in split-plot design.

Pigeonpea (UPAS 12O) and intercrops (green gram, PS-l6 and sorghum, CSH 6) were sown on 1 July, l982. A basal dose of 2O kg N/ha was applied at sowing. An additional dose of 30 kg N/ha was top-dressed by the side of sorghum rows in pigeonpea + sorghum intercropping system 3O DAS. The plant density of intercrops in paired row pattern was kept 50 per cent higher than uniform row pattern by raising three and one row respectively.

Planting pattern had no effect on yield attributes, grain yield and nutrient uptake by pigeonpea (Table 1 and Fig. 1). Paired row pattern recorded relatively higher yield and nutrient uptake by intercrops as compared with uniform row pattern possibly owing to higher plant density/unit area and in-built energy harvest mechanism. The total production in terms of pigeonpea equivalent and total nitrogen and phosphorus uptake in the system as a unit, however, remained unaffected. Intercropping adversely affected yield, yield parameters and nutrient uptake by pigeonpea (Table 1 and Fig. 1). The three systems were in the following order, sole pigeonpea > pigeonpea + greengram > pigeonpea + sorghum. Tall growing sorghum intercrop offered relatively more competition for light and nutrients than green gram and the active growth period of sorghum coincided exactly with that of pigeonpea resulting in lower yields and nutrient uptake by pigeonpea. The extra-early (120 days) variety of pigeonpea used in the present study could not compensate for the setback caused by the competition due to intercropping of green gram which occupied the land for about two months in the crop season.

Pigeonpea intercropped with green gram recorded the highest pigeonpea equivalent (16.1 q/ha) followed by sole pigeonpea (15.0 q/ha) and pigeonpea + sorghum intercropping system (10.4 q/ha). Nitrogen and phosphorus uptake by pigeonpea were adversely affected by intercropping, the effect being more conspicuous in and pigeonpea + sorghum system. Pigeonpea intercropped with green gram recorded markedly higher total nitrogen uptake than sole pigeonpea and pigeonpea + sorghum, with the latter two being at par. All the three systems differed significantly in respect of phosphorus uptake. Sorghum intercrop made major contribution to nutrient uptake in pigeonpea + sorghum system since the growth and grain yield of pigeonpea were drastically reduced in this system.

Yield and yield components of pigeonpea and pigeonpea equivalent increased with increasing levels of phosphorus up to 60 kg P2O5/ha (Table 1). The positive response to phosphorus could be attributed to low phosphorus status of the soil. The uptake of nitrogen and phosphorus by pigeonpea and the total uptake by the system showed a consistent increase with increasing rates of phosphorus up to 90 kg P2O5/ha (Fig. 1). Similar trend was also noticed in case of intercrops. The improvement in nutrient uptake by phosphorus application could be assigned to better plant growth leading to higher dry matter yields and increased nutrient content.

The interaction effect of intercropping systems and phosphorus on grain yield of pigeonpea and pigeonpea equivalent indicated that comparable yields of pigeonpea were obtained with 30 kg P2O5/ha in sole pigeonpea and with 60 kg P2O5/ha in pigeonpea + greengram (Table 2). Further, sole pigeonpea had higher yields than pigeonpea intercropped with greengram at all rates of phosphorus except 90 kg P2O5/ha, where both of them were at par. In terms of pigeonpea equivalent, sole pigeonpea and pigeonpea + greengram showed favorable response up to 6O kg P2O5/ha only, while it increased with increasing rates of phosphorus up to 9O kg P2O5/ha in pigeonpea + sorghum system.

The relationship between grain yield of pigeonpea or pigeonpea equivalent and the rates of phosphorus was quadratic. The regression equations computed are given in Table 3.

The optimum dose of phosphorus was relatively higher in intercropping systems since it involved more plants per unit area. Pigeonpea + green gram system showed relatively better response to applied phosphorus both in terms of gram yield of pigeonpea and its equivalent.

The fertility status in terms of total nitrogen and available potash at harvest remained unaffected of various treatments (Table 1). Plots of sole pigeonpea had higher available phosphorus than those of pigeonpea intercropped with sorghum probably due to a higher requirement of this nutrient by both components in the latter system. The phosphorus status of soil showed gradual improvement with every increment of applied phosphorus attributable to its solubilization by legume roots and residual amount of applied phosphorus.

REFERENCE

DE, R., Gupta, R.S., Singh, S.P., Pal, M., Singh, S.N., Sharma, R.N. and Kaushik, S.K. (1978). Inter-planting of maize, sorghum, and pearl millet with short duration legumes. Indian J. agric. sci. 48: 132-137.