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Present study was carried out at the research farm of ICAR-Central Tuber Crops Research Institute, Thiruvananthapuram, Kerala during 3 summer seasons of 2016–17, 2017–18 and 2018–19 to assess the crop water requirement of upland taro (Colocasia esculenta L. Schott) and to arrive at a suitable irrigation schedule under humid tropical conditions of Kerala. The experiment was conducted in randomized block design (RBD), with 7 treatments as 5 levels of drip irrigation, [50% (I1), 75% (I2), 100% (I3), 125% (I4) and 150% (I5) of the crop evapotranspiration, ETc], furrow irrigation and a rainfed crop with 3 replications. Crop water requirement was calculated as same as crop evapotranspiration (ETc) assuming that there is no other water losses. Pooled analysis of the data collected for three seasons indicated that, I3, drip irrigation at ETc 100% is optimum for achieving maximum cormel yield and optimum water productivity. The optimal water requirement for upland taro was observed as 610–628 mm, including effective rainfall, based on the crop, soil and climatic parameters. The information will support the farmers to develop irrigation plans in advance during summer season, and for ensuring effective usage of irrigation water in water scarce areas, in this era of climate change.

An experiment was laid out in split-plot design with three replications. Main and sub plots consisted of drip irrigation [I1- at 80% of cumulative pan evaporation (CPE) during 1-270 days after planting (DAP), I2-at 100% of CPE during 1-90 DAP + at 80% of CPE during 91-270 DAP and I3-at 100% of CPE during 1-270 DAP] and fertigation (F1-N-P2O5-K2O 100-90-100 kg/ha, F2-N-P2O5-K2O 120-90-120 kg/ha, F3-N-P2O5-K2O 140-90-140 kg/ha and F4- N-P2O5-K2O 160-90-160 kg/ha) treatments respectively. The drip irrigation treatments I1(F2) and I2(F2) saved 17.3% (690 m3/ha) and 7.8% (310 m3/ha) irrigated water over surface flood irrigation at same level of fertilizer application (N-P2O5-K2O 120-90-120 kg/ha) (check). Electricity consumption saved 104 (17.4%) and 47 (7.9%) kWh/ha by adopting drip irrigation levels I1(F2) and I2(F2), respectively over check. The system productivity with the application of N-P2O5-K2O 100-90-100 kg/ha (F1) along with drip irrigation at I2 was comparable with check which indicated a net saving of N-K2O 20-20 kg/ha. The net income from drip irrigated greater yam (Dioscorea alata L.) + maize (Zea mays L.) under I1(F2) and I2(F2) was about 9 100 and 62 100 ₹/ha higher than the crop cultivated with surface flood irrigation (check), respectively. Greater system productivity in the treatments I2F4 (31.8%) and I2F3 (29.9%) over check indicated fertilizer responsiveness under drip fertigation. Considering environmental and economical impact, the partial deficit drip irrigation and fertigation treatment I2F3 could be the best for greater yam+maize intercropping system.

Consumer awareness regarding the impacts of high-input chemical intensive conventional agriculture on the soil, environment and human health has spurred the growth of organic agriculture systems. Organic agriculture ensures sustainable production, safe food and environmental conservation. It is estimated that more than 95% of organic production is based on crop varieties that were bred for the conventional high-input sector. Such varieties lack important traits required under organic and low-input production conditions. There is dearth of information on the response of varieties to organic management. Field experiments were conducted for two years during 2010 and 2011 at the Central Tuber Crops Research Institute, Thiruvananthapuram, to compare the growth, yield and quality performance of five elephant foot yam [Amorphallus paeoniifolius (Dennst.) Nicolson] varieties (Peerumade local, Gajendra, Sree Padma, Vegetable and Fruit Promotion Council Keralam (VFPCK) local and Sree Athira) and soil physicochemical and biological properties under organic vs conventional systems in split plot design. Varieties × production systems interaction was not significant for most of the variables. The elite as well as the local varieties responded equally well to both the systems with average corm yields of 27.72 tonnes/ha under organic and 28.55 tonnes/ha under conventional practice. The var. Gajendra responded well to organic management producing higher yield (+10%). The other varieties had lower yield losses (-2.5-15.0%) under the organic system. The corms of the varieties had slightly higher dry matter, sugar, P, K and Fe contents under organic system. The varieties also exerted similar effects on soil physicochemical and biological properties, when tested under organic and conventional management. However, Gajendra and Sree Padma effected significantly higher organic C status under organic management due to greater biomass addition on account of their innate robust plant type. In general, there was significant improvement in soil pH and bacterial count, slight lowering of bulk density and particle density, improvement in water holding capacity, secondary and micronutrient status, N fixers and dehydrogenase enzyme activity in the organic system.

Cassava (Manihot esculenta Crantz) is an important food crop of India cultivated in an area of 228 000 ha for food, feed and fuel, contributes to food security, equity, poverty alleviation and environmental protection. This study examined the projected climatic changes in the major cassava growing environments of India and also calibrated and evaluated the EcoCrop model to study the impact of 2030 climate on cassava climate suitability in the major growing environments of India. The current climate and future climate projections of 22 GCMs from the SRES-A1B emission scenario were used for the study. The projected change in annual mean temperature and total annual precipitation in the major growing areas ranged from 0.9 to 1.2ºC and from 6.8 to 112.4 mm, respectively. The calibrated data were used to drive the EcoCrop model to find out the suitability of current and future climatic conditions. The change in suitability for all the 22 GCMs used was calculated on pixel basis and the mean suitability change indicate that cassava is actually positively impacted in the current growing areas of India with -2.2 to 15% changes in climate suitability. This study concluded that cassava is potentially highly resilient to future climatic changes and it can become a future crop in India, where other crops would fail due to climate change.

Elephant foot yam [Amorphophallus paeoniifolius (Dennst.) Nicolson] is an important tuber crop grown in many parts of India for its starchy corm and the average yield of this crop is far below the potential productivity of 100 tonnes/ha. One of the reasons attributed to the lower yield is the imbalanced application of essential plant nutrients. Site specific nutrient management (SSNM) is the application of plant nutrients based on the soil and crop need, yield target and developed with the aid of models such as QUEFTS. This paper gives the result of four year study conducted to calibrate and validate the QUEFTS model for elephant foot yam cultivation and the development of SSNM zonation maps and secondary and micronutrient fortified customised fertilizers for the crop in major growing environments of India. Data collected from different field experiments conducted in major elephant foot yam-production regions of India during 1968 to 2011 were used to calibrate the model. The derived parameters of minimum and maximum accumulation of N (130 and 460), P (900 and 2100) and K (100 and 170) are proposed as standard borderline values in the QUEFTS model for elephant foot yam. A linear increase in corm yield was suggested by the model with N, P and K uptakes of 3.97, 0.71, and 7.05 kg N, P and K/1 000 kg corm. The average NPK ratio in total plant dry matter was 5.56:1:9.88. Based on these results, the model was calibrated using historical data as well as by conducting field experiments. It can be observed that fertilizer best management practices by SSNM resulted in an average actual corm yield of 33.45 tonnes/ha, whereas, the model predicted a yield of 35 tonnes/ha. The results of the study showed good agreement between predicted and measured corm yields during the four years, which indicated that the calibrated model can be used to improve NPK fertilizer recommendations for elephant foot yam in India. Based on the results and using soil fertility maps and agro ecological unit maps, SSNM zonation maps and secondary and micronutrient fortified customised fertilizers were developed for major elephant foot yam growing environments of India.

Cassava (Manihot esculenta Crantz) is an important subsidiary food and industrial raw material in the tropics. Considering the importance of the crop, an on farm experiment was conducted to study the effect of NPK fertilizer rate and biocontrol agents (Trichoderma and Pseudomonas fluorescens) and biofertilizers (Azospirillum, AM fungi and phosphorus solubilising bacteria) on soil chemical, biochemical and microbial biomass carbon in cassava growing Vertisols of Tamil Nadu during 2008 and 2009. The study was conducted in split plot design with two levels of NPK fertilizer as main plot treatments and eight microbial inoculations as subplot treatments. Azospirillum with Trichoderma (170.58 kg/ha), AM fungi with Trichoderma (57.85 kg/ha) and Trichoderma alone (473.70 kg/ha) significantly increased available nitrogen, phosphorus and exchangeable potassium by reducing the amount of NPK. Pseudomonas fluorescens with Trichoderma at 50 per cent recommended NPK rate increases the available iron in soil. The AM fungi with Trichoderma significantly increased available manganese and zinc compared to other inoculations at 50 per cent recommended NPK rate. Azospirillum with Trichoderma at the recommended NPK rate increased the urease enzyme activity (835.21 mg urea hydrolysed/g soil/h) compared to other treatments. The soil application of all cultures at 50 per cent recommended NPK rate increased soil dehydrogenase and b glucosidase enzyme activities. Interaction effect showed significantly higher microbial biomass carbon in AM fungi with Trichoderma at 50 per cent recommended NPK rate (3792.45 µg/g soil) and was on par with soil application of all cultures at 100 per cent and 50 per cent recommended rate. In general microbial inoculations at 50 per cent recommended rate gave on par or significantly higher results compared to uninoculated control at recommended NPK rate.