Leaf-Litter Decomposition in an Oak-Conifer Forest in Himalaya: The Effects of Climate and Chemical Composition

The decomposition rates of certain dominant litter species inan undisturbed oak-conifer forest in the Kumaun Himalaya wereinvestigated by enclosing pre-weighed, newly senesced leavesin litter bags, placing these bags on the forest floor and determiningthe weight loss by recovering the bags at monthly intervals.Among the species examined, Daphne cannabina decomposed fastestand Cupressus torulosa decomposed most slowly. The former took6 months for complete decomposition, while Cupressus torulosadecomposed to about 72 per cent in 18 months. A linear combinationof rainfall and temperature explained 80 per cent of the variabilityin monthly weight loss. The rate of decomposition was also relatedto the initial chemical composition of the litter. Initially,several constituents showed a significant relation with decomposition;these are nitrogen, calcium, water soluble compounds, totalnonstructural carbohydrates, lignin, acid detergent cell wallcomponents and fibre. Of these, lignin and fibre contents showeda negative relation with weight loss while the others were positivelyrelated. As decomposition progressed, only nitrogen, lignin,ADCW and fibre content remained important. With further lapseof time only two constituents, nitrogen and lignin, remainedimportant. Among these the effect of nitrogen declined withtime while that of lignin increased. A linear combination ofnitrogen and lignin explained 59 per cent variability in theannual weight loss.     

Effect of Irrigation, Mulch and Nitrogen on Yield and Composition of Japanese Mint (Mentha arvensis L. subsp. haplocalyx var. piperascens) Oil

Effects of irrigation, mulch and nitrogen on yield and composition of Japanese mini ( Mentha arvensis L. subsp. haplocalyx Briq. var piperascens) oil were studied using a replicated experiment. Two harvests were obtained 120 davs atter planting and 75 davs after the first harvest. Significantly higher drv matter and essential oil yields were obtained with frequent irrigations (50 mm Cumulative Pan Evaporation), application of mulch and Nitrogen. The economic optimum rate of N was 215 Kg ha^-1. The essential oil from the first harvest was richer in menthol (78.8%) than the oil obtained from second harvest (75.2%). Soil moisture extraction was maximum between 15 and 30 cm soil depths. Consumptive use, water use efficiency and moisture use rate-were maximum under higher irrigation levels and mulch application which reflect that more availability of moisture in soil profile with frequent irrigations and application of mulch.     

Ultrastructure of the host-pathogen interface of Peronospora viciae in cultivars of pea which show different susceptibilities

The ultrastructure of interactions of pea downy mildew ( Peronospora viciae ) on the leaves and petioles of two cultivars of pea, Superb and Maro, was examined. Tissue fixed at the time of sporulation (10 days after inoculation) revealed that many of the intercellular hyphae in Maro were showing evidence of partial or complete autolysis. The penetration matrices were enclosed in a thicker layer of callose-like material than in Superb, and many of the haustoria had collapsed, distorted profiles. Analysis of organelles lying close to the extra haustorial membrane revealed fewer associations with endoplasmic reticulum in Superb.     

Long-term conservation agriculture and intensified cropping systems: Effects on growth, yield, water, and energy-use efficiency of maize in northwestern India

Conservation agriculture(CA)-based best-bet crop management practices may increase crop and water productivity, while conserving and sustaining natural resources. We evaluated the performance of rainy season maize during 2014 under an ongoing long-term trial(established in 2008) with three tillage practices, i.e., permanent bed(PB), zero tillage(ZT), and conventional tillage(CT) as main plots, and four intensified maize-based cropping systems, i.e., maize-wheat-mungbean, maize-chickpea-Sesbania(MCS), maizemustard-mungbean, and maize-maize-Sesbania) as subplot treatments. In the seventh rainy season of the experiment, maize growth parameters, yield attributes, yield, and water-and energy-use efficiency were highest at fixed plots under ZT. Maize growth parameters were significantly(P 0.05) superior under ZT and PB compared with CT. Maize yield attributes, including cobs per m~2(7.8), cob length(0.183 m), grain rows per cob(13.8), and grains per row(35.6), were significantly higher under ZT than CT; however, no significant effect of cropping systems was found on maize growth and yield attributes. Zero tillage exhibited the highest maize productivity(4 589 kg ha~(-1)). However, among the cropping systems, MCS exhibited the highest maize productivity(4 582 kg ha~(-1)). In maize, water use was reduced by 80.2–120.9 mm ha-1under ZT and PB compared with CT, which ultimately enhanced the economic water-use efficiency by 42.0% and 36.6%, respectively. The ZT and PB showed a 3.5%–31.8% increase in soil organic carbon(SOC) at different soil depths(0–0.45 m), and a 32.3%–39.9% increase in energy productivity compared with CT. Overall, our results showed that CA-based ZT and PB practices coupled with diversified maize-based cropping systems effectively enhanced maize yield and SOC,as well as water-and energy-use efficiency, in northwestern India.     

Impact of irrigation regimes on regeneration and growth of Prosopis cineraria in arid areas of Indian Thar

An experiment was initiated in 2008 to evaluate the impact of irrigation regimes on germination and growth patterns of seedlings of Prosopis cineraria in the arid areas of Thar, India. Seeds collected from dried pods of P. cineraria were sown in polybags placed in nursery beds. Different irrigation regimes were provided to different beds and data regarding germination and growth were recorded to study natural regeneration. The study revealed that irrigation regimes significantly affected the germination and growth of P. cineraria under nursery conditions. The germination rate declined as the irrigation regime shifted from a daily to a fortnightly basis. Height of the seedlings also declined with a decrease in the intensity of irrigation. Thus, it can be concluded that germination and growth of seedlings of P. cineraria under nursery conditions can be enhanced by providing irrigation at regular intervals.     

Translocation of 2,4-D, asulam and amitrole in water hyacinth

In glasshouse experiments foliar application or ¹⁴C-labelled herbicides to water hyacinth plants at the 4-leaf stage indicated that amilroie transport from the treated leaf blade was faster and greater than 2.4-D. but a little less than asulam. From the treated leaf 14·2, 25·9. 39·7. 44·5 and 51·8% of the recovered ¹⁴CNamitrole was translocated at intervals of 6 h. and 1. 3. 6 and 12 day., respectively. Both xylem and phloem transport of asulam and amitrole was evident, whereas 2.4-D moved only from ‘source to sink’. Movement of the herbicides from the mother to the connected daughter plant or vice versa was dependent upon the size of the latter. Maximum transport of these herbicides in either direction took place at the 2-leaf stage of daughter plants. With any increase or decrease in the number of leaves on daughter plants, the transport of herbicides was reduced. As an exception, daughter plant to mother plant movement of amilroie was maximum at the 1-leaf stage. After extraction, fractionation and TLC separation of foliage applied ¹⁴C-2.4-D 76–4 and 72·1% of the radioactivity was detected in the chloroform phase of the leaf extract at 3 and 6 day intervals, respectively. In another pot culture experiment, it was observed that after spraying the mother plants with 2.4-D-amine at 0–75 kg/ha the connected daughter plants at 1 to 4-leaf stages werckilled if the culture solution was contaminated while spraying, or by dying leaves. When contamination was totally avoided, the connected but unsprayed daughter plants at 3 to 4-feaf stages survived.     

Sheath rot and leaf blight – a new disease of Java citronella caused by Rhizoctonia solani

A new disease of Cymbopogon winterianus , characterized by symptoms of sheath rot and leaf blight, has been observed in the Tarai region of Uttar Pradesh (IN). The pathogen has been isolated and identified as Rhizoctonia solani.     

Effects of isoproturon on photosynthesis in susceptible and resistant biotypes of Phalaris minor and wheat

Wheat (cv. WH-147) and five biotypes of Phalaris minor Retz. (KR-1, H-4, K-2, H-2 and J-1) were treated with isoproturon in controlled environmental conditions to assess their level of resistance. Resistance of P. minor to isoproturon was found in the order of KR-1 > H-4 > K-2 > H-2 = J-1. Compared with the susceptible (S) biotype (H-2), the resistant (R) biotypes (KR-1. H-4 and K-2) of P. minor required 13.0, 4.5 and 2.7 times higher doses of isoproturon for a 50% reduction in growth (GR₅₀) and 2.4 times that of the S biotype (H-2) by wheat. The corresponding figures for KR-1, H-4, K-2 biotypes and wheat were 18, 4.1, 2.4 and 4.6 times based on dry weight reduction. The effect of isoproturon on photosynthesis was studied in vitro using five biotypes of P. minor and in viro with wheat. KR-1 (R) and H-2 (S) biotypes of P. minor. Under in vitro treatment conditions isoproturon inhibited the photosynthesis of all five P. minor biotypes, whereas in vivo the recovery was greater in the R biotype than in the wheat and the S biotype. Effects on chlorophyll fluorescence were also measured in wheat and the KR-1 (R) and H-2 (S) biotypes of P. minor. A 4-h treatment of excised leaves incubaled in isoproluron solution (0.025 and 0.05 mm concentration) resulted in a decreased fluorescence coefficient (F_v F_m ratio in which F_v= variable fluorescence (F_m - F^o): F_m= the maximum fluorescence and F_o= initial fiuorescence) in wheat (Triticum aestivum L.) and both biotypes of P. Minor. The recovery was, however, greater in the R biotype than in wheat and it was completely recovered within 24 h. No recovery was recorded in the case of the S biotype of P. minor and a greater recovery time was required for wheat than the R biotype. The higher dose required for growth inhibition in the R biotype and rapid recovery of oxygen evolution and fluorescence coeflicient under in viro conditions together with the absence of selectivity in vitro suggests that the target site was unaffected. It can be conjectured that resistance to isoproturon is most probably because of enhanced metabolism or sequestration of isoproturon, resulting in decreased target site delivery.