Recent progress in cassava agronomy research in India

Cassava is an important crop in India, with an area of 289,000 ha and production of 5.6 million t of fresh roots in 1991. It is mainly cultivated in Kerala, Tamil Nadu, Andhra Pradesh and in the Northeastern states. A large variation in cassava consumption exists between urban and rural areas in India. About 70% of cassava production in Kerala is used for food. In Tamil Nadu, however, only 25% is used for human consumption, while the rest is used for industrial utilization, mainly for starch production. About 17% of cassava production in the country is used for animal feed. Cassava is used in industry for production of starch, sago, liquid glucose, dextrin, vitamin C, gums and high-fructose syrup. Earlier agronomy research concentrated on the development of cultural practices and soil fertility management for cassava grown in monoculture. Recently, research has focused on the development of cassava-based cropping systems, soil fertility management with emphasis on micronutrients and bio-fertilizers (especially VA-mycorrhiza), low-input technology, water management and production practices for non-traditional areas. Short-duration cassava cultivars were shown to produce higher root yields at closer spacing of 75x75 cm, while for cassava grown under coconuts a plant population of 8000/ha was found to be optimum. Under intercropping with groundnut or cowpea the paired-row cassava system performed best. In acid infertile soils in Kerala, continuous cropping of cassava with application of only NPK chemical fertilizers resulted in a depletion of Ca, Mg, Cu and Zn in the soil. From the study on interrelationships of cations the optimum doses of K, Ca and Mg were found to be 146 kg K^O, 56 kg Ca and 37 kg Mg/ha. Incorporation of ZnSO at 12.5 kg/ha increased the root yield 12%. An NPK application of 50:62:62 kg/ha was sufficient for the cassava-ground nut intercropping system if the haulms of groundnut were turned back into the soil. For cassava grown under coconut an NPK rate of 50:50:100 kg/ha gave higher net returns. For rice-cassava sequential cropping on paddy soils the P application rate to cassava could be reduced to 25 kg P O /ha. In calcareous soils of Tamil Nadu short duration cassava cultivars performed better at lower levels of NPK (75:25:75 kg/ha). Application of a liquid NPK fertilizer at the rate of 8-8-8 kg/ha was equally effective as the same rate applied in solid form. Inoculation of VA mycorrhiza (VAM) enhanced the dry matter production, root yield and uptake of P, Cu and Zn in cassava. For successful field inoculation a nursery techniquewas developed. To realize the production potential of high-yielding cassava, the application of NPK at 150:100:150 kg/ha and supplementary irrigation at an IW/CPE ratio of 1 were found necessary. In cassava-groundnut intercropping systems, supplementary irrigation during drought periods at 25 mm/week enhanced the yield of both crops. Studies on effects of subsoil moisture on cassava showed that a shallow water table (around 40 cm from the surface) depressed root yields

Progress in agronomy research in India

Nutritional studies of cassava have shown that in high-P acid laterite soils, there was no response to P application during four years of consecutive cropping. In low-P soil, even though cassava initially responded to 100 kg P2O5/ha, the response gradually declined. The optimum economic dose of P for cassava in acid laterite soil is about 45 kg P2O5/ha. Studies on the NPK requirement of a short duration variety of cassava in a rice-based cropping system, showed that there was a response to the application of 100 kg each of N and K2O/ha, but no significant response to P. In upland rice fields the sequential cropping of vegetable cowpea and cassava can eliminate the need for FYM application by incorporating the crop residue of vegetable cowpea before planting cassava. Application of N and K had a significant effect on root yield of short-duration (7 months) lines of cassava, CI-649 and CI-731, up to 75 kg N/ha and 100 kg K2O/ha. Studies conducted by Kerala Agric. Univ. have shown that up to 50% of the KC1 requirement of cassava can be substituted by sodium chloride (NaCl) without any deleterious effect on crop yield. Another study revealed that under partial shade of adult coconut palms (76% PAR), rainfed cassava (cv Sree Visakham) yielded 77 % of that grown in the open. Transplanting of rooted cassava cuttings, inoculated with the VA-mycorrhizal fungus (VAMF) Glomus microcarpum var. microcarpum, was found to enhance the total dry matter and root yield, besides increasing the concentration of micronutrients like Cu and Zn in the leaves. Mass inoculation with VAMF in farmers' fields by planting rooted infected cuttings showed that 70% of the farmers were convinced that they could obtain a higher yield of roots using this practice. The present practice of planting cassava is to plant stakes directly in the field with the onset of pre-monsoon rains. In this practice, the uncertainty of rainfall may cause poor establishment. In order to overcome this, cassava stakes are first planted in a nursery at a very close spacing of 4.5 x 4.5 cm so as to accommodate about 500 stakes/m2. Uprooting is easiest when a saw dust media is used in the nursery. Root yield was not affected by the time of uprooting and transplanting in the field between 15 and 25 days, but beyond that age there was a significant reduction in root yield. This technique can be effectively used when short duration varieties are grown under rainfed conditions in areas where rainfall is limited to 4 to 5 months per year. The plants are first raised in a nursery for 25 days and then transplanted in the field with the onset of rains