Screening of kenaf (Hibiscus cannabinus L.) genotypes for low temperature requirements during germination and evaluation of feasibility of seed production in Italy

Kenaf (Hibiscus cannabinus L.), an annual plant of the family Malvaceae, with potential use as a non-wood fiber source is a relatively new crop in Italy where it can be used in the manufacture of paper and pulp products. Cultivars differ markedly in their response to daylength, but stem growth generally declines rapidly following the onset of flowering such that under Italian conditions sowing for fiber production has to be carried out early to allow maximum growth before floral initiation. Sowing is generally delayed until soil temperature exceeds 12°C (approximately the middle of May), and therefore it is important to evaluate genetic diversity in response to low temperature during the germination stage to determine which kenaf cultivars are suited to early sowing. These trials screened various lines to identify those able to germinate at low temperature and therefore suitable for early sowing. The lines were also grown to evaluate photoperiodic requirements and seed yield in the trial environment (Experimental Centre of Rottaia, Pisa, central Italy, 43°40′N latitude;10°19′E longitude). In addition, the germination characteristics of seed obtained here were tested at low constant temperature (8°C) and at alternating 20–30°C temperature. Seed belonging to 15 lines – produced in Australia and selected for tolerance to low temperature – showed high germination percentage at 8°C in comparison with Tainung 2, a cultivar sensitive to low temperature and produced in USA (75 and 12% as overall mean of lines and Tainung 2, respectively). Lines differed significantly in their response to temperature both in germination percentage and mean germination time. Lines showed a wide range of duration of vegetative period. Flowering took place from 31 July to 23 August in most lines, and they are therefore considered early-maturing-types. Lines differed in duration of the period from emergence to seed maturity (from 134 to 187 days), in seed yield per plant (from 0.9 to 27.7 g plant⁻¹), and harvest index (from 0.3 to 16.6%). In some lines, flowering occurred in mid-August and seed filling was then not completed due to low air temperature and unfavourable moisture conditions. Seed produced in central Italy had low quality due to more rapid deterioration and susceptibility to fungal pathogens. Sensitivity to low temperature during germination was greater in most lines and germination percentages were considerably lower than for seed produced in north-eastern Australia. Environmental conditions in central Italy appear inadequate for seed production.     

Seed germination response of cuphea to temperature

Cuphea (Cuphea viscosissima Jacq. × C. lanceolata W.T. Aiton; PSR23) is a potential new oilseed crop. Its oil is high in medium-chain fatty acids that are suitable for detergent/cleaner applications and also for cosmetics. The objective of this study was to determine the critical temperatures for cuphea seed germination. To determine the base, maximum, and optimum temperatures for seed germination, mature cuphea seeds were harvested from plants grown at Prosper, ND, in 2004, 2005, and 2006. Seeds were germinated on a temperature-gradient bar varying between 5 and 35 °C. Cumulative germination was calculated for each temperature treatment. Base temperature (T_b) and optimum temperature (T_o) were estimated from the third-order polynomial temperature-response functions for each year. In addition, germination rate per day was used in a linear model to estimate the base temperature below which germination rate was equal to zero (T_b), and the maximum temperature above which germination was equal to zero (T_m). The optimum temperature (T_o) was calculated as the intercept of sub-optimal and supra-optimal temperature-response functions. Through the third-order polynomial temperature-response functions and the sub-optimal/super-optimal intercept approaches, we were able to generate six estimates for each critical value. Estimates of the base temperature for cuphea seed germination ranged between 3.3 and 11 °C, with the most reliable estimates between 6 and 10 °C, similar to many warm-season crops such as corn (Zea mays L.) and sorghum (Sorghum bicolor L.). The optimum temperature for cuphea seed germination ranged between 18.5 and 24 °C with a mean value of 21 °C. The maximum temperature for seed germination ranged 33–38 °C. On this basis, a cuphea planting date after 20 May is recommended for east-central North Dakota.     

The influence of rainfed and limited irrigation conditions and early vs. late plantings on kenaf as a potential industrial crop in the southern High Plains,USA

Kenaf (Hibiscus cannabinus L.) is a nonwoody fiber source with many uses. To evaluate the dry matter yield potential of kenaf at two locations in the southern High Plains of the USA and the effects of late planting/late emergence as a possible replacement for hail damaged cotton, four varieties were grown in 2004 and 2005 at New Mexico State University's Agricultural Science Centers at Clovis, under limited irrigation, and Tucumcari, under rainfed conditions. Each study was a randomized complete block design having four replicates. A year × location interaction existed (P < 0.0469) for kenaf yield largely due to precipitation amount and distribution. Either late planting or late emergence due to low soil moisture at planting significantly reduced yields (3.62 vs. 0.63 Mg ha^?1 for mid-May planting and emergence and early July emergence or planting, respectively, P < 0.0001). Consequently, kenaf would not be suitable for recovering input costs when planted after failure of cotton. The very late maturing variety Gregg had consistently lower numeric yields than Dowling, Everglades 41, and Tainung 2 in all comparisons, with the strongest trend within the emergence date comparison (P < 0.0912). Kenaf varieties should be selected for any location that finish blooming approximately three to four weeks prior to the average first autumn freeze to allow for maximum growth.     

Physiological age index: a new,simple and reliable index to assess the physiological age of seed potato tubers based on haulm killing date and length of the incubation period

Chronological and physiological age of seed tubers have major impacts on potato yields. This paper presents a new, simple and reliable physiological age index (PAI) that considers and reconciles the effects of chronological and physiological age. PAI calculation is based on the haulm killing date of the seed crop (T₀) and the end of the incubation period of seed tubers, measured under standardized conditions. The PAI formula is T₁/T₂, where T₁ is the time from haulm killing date (T₀) to possible planting date and T₂ the time from T₀ to the end of the incubation period. The PAI expresses physiological ageing of seed potato tubers within a range from 0 (for physiologically young) to 1 (old) tubers. To test the PAI existing data were re-evaluated and re-elaborated and specific experiments regarding seed origin and storage conditions for different cultivars were performed during 1994–1999. The PAI proved useful in assessing differences due to differences in growing conditions, cultivar, haulm killing, seed origin and storage system, and pre-planting treatments. For example, for cv. Spunta 6 days after haulm killing the PAI was 0.025 and after 100-storage days the PAI was 0.56, 0.52 and 0.49 for seed tubers stored in heaps in the field, at relatively high temperatures, natural diffuse light and a cold (4°C) and ventilated store, respectively. The PAI is related to ground cover duration and yield of the future crop. For a PAI of 0.55 tuber yield was 55 t ha⁻¹, while for a PAI of 0.80 tuber yield was 40 t ha⁻¹. The PAI is easy to measure, non-invasive, objective, reproducible and reliable and could be used for modelling purposes to describe performance of seed tubers.     

Seed physiological maturity in Cuphea

Cuphea (Cuphea viscosissima Jacq. × C. lanceolata f. silenoides W.T. Aiton, line PSR23) is a new crop being developed in the North Central United States, as an industrial oilseed crop. Cuphea PSR23 seed oil is rich in medium-chain-length fatty acids such as capric acid used to manufacture soaps and detergents. The objective of this research was to determine the time when physiological maturity of cuphea seed is reached and how seed development affects seed moisture, weight, oil content, fatty acid content, germination, and seedling vigor. To evaluate seed development, 2000 cuphea flowers were tagged at anthesis in the field at Prosper, North Dakota in 2004 and 2005. Each flower was tagged when open and the position on the main stem or branch was recorded. Two hundred capsules from the tagged flowers were harvested at 3- to 4-d intervals from 5- to 48-d post anthesis (DPA). Seed weight increased as a function of growing degree days (GDD) and the days from anthesis. Physiological maturity occurred when maximum dry seed weight was attained. Seed weight increases followed the Gompertz function with a R² = 0.90 (2004) and R² = 0.95 (2005). All capsules, regardless of their position on the stem, followed the same growth function for seed weight. The maximum dry seed weight estimated by the Gompertz function was 3.61 for 2004 and 3.58 mg seed⁻¹ for 2005. Physiological maturity estimated with a quadratic function occurred at 38 DPA or 270 GDD in 2004. In 2005, physiological maturity occurred at 26 DPA or 265 GDD. As a visual indicator when the capsules split-open seeds inside that capsule are physiologically mature. Seed moisture decreased from 900 g kg⁻¹ at 37 GDD post anthesis to 450 g kg⁻¹ at 319 GDD post anthesis in 2004; however, in 2005 seed moisture decreased from 850 to 81 g kg⁻¹ at 293 GDD post anthesis. Seed germination increased as seed developed and it was 83% when harvested 234 GDD post anthesis. Oil content increased from 98 g kg⁻¹ at 37 GDD post anthesis to 279 g kg⁻¹ 319 GDD post anthesis. Fatty acid composition varied throughout seed development. Seed development for 111 GDD and greater had more than 66% of capric acid (10:0). Cuphea should be harvested after 265 GDD post anthesis when most capsules on the main stem are split-open, have attained maximum seed weight, germination, seedling vigor, and oil content.     

Large applications of fertilizer N at planting affects seed protein and oil concentration and yield in the Early Soybean Production System

An inverse relationship between soybean [Glycine max (L.) Merr.] seed protein and oil concentration is well documented in the literature. A negative correlation between protein and yield is also often reported. The objective of this study was to determine the effect of high rates of N applied at planting on seed protein and oil. Nitrogen was surface-applied at soybean emergence at rates of 290 kg ha⁻¹ in 2002, 310 kg ha⁻¹ in 2003, and 360 kg ha⁻¹ in 2004. Eight cultivars ranging from Maturity Group II–IV were evaluated under the Early Soybean Production System (ESPS). However, not all cultivars were evaluated in all 3 years. Glyphosate herbicide was used in all 3 years and a non-glyphosate herbicide treatment was applied in 2002. Cultivars grown in 2003 were also evaluated under an application of 21.3 kg ha⁻¹ of Mn. All cultivar, herbicide, and Mn treatments were evaluated in irrigated and non-irrigated environments with fertilizer N (PlusN treatment) or without fertilizer N (ZeroN treatment). When analyzed over all management practices (years, cultivars, herbicide, and Mn treatments), the PlusN treatment resulted in a significant decrease in protein concentration (2.7 and 1.9%), an increase in oil concentration (2.2 and 2.7%), and a decrease in the protein/oil ratio (4.7 and 4.6%) for the irrigated and non-irrigated environments, respectively. However, the overall protein and oil yield increased with the application of fertilizer N at planting (protein: 5.0% irrigated, 12.7% non-irrigated and oil: 9.9% irrigated and 18.9% non-irrigated). These increases were due to the increase in seed yield with the application of large amounts of fertilizer at planting. Additionally, a significant correlation (r = 0.45, P = 0.0001) was found between seed protein concentration and seed yield. No significant correlation was found between seed oil concentration and seed yield. The data demonstrate the inverse relationship between protein and oil and indicate that large amounts of N applied at planting do not change this relationship.     

Cardinal temperatures for germination and early growth of two Lesquerella species

Lesquerella (Lesquerella fendleri) is a potential alternative crop that is being studied for commercial oilseed production. Understanding the minimum temperatures for germination and seedling growth is important for determining potential areas for lesquerella production. The objectives of this study were to determine the cardinal temperatures for germination and seedling growth, and to screen ecotypes for germination and growth characteristics. A temperature gradient table arrangement was used to observe seed germination over a range of temperatures, and time to germination and shoot appearance. Times to 5 mm root length and 5 mm shoot length were also measured to assess cardinal temperatures for seedling survival and growth. Two different species were examined, L. fendleri and a species we refer to as ‘L. pallida aff.’ because it differed from typical L. pallida plants in chromosome number and in oil quality. We concluded that both germination and growth of L. pallida aff. occurred fastest at 22 °C, whereas L. fendleri germinated earlier at 18 °C, but grew faster at 22 °C. L. pallida aff. also had lower germination than L. fendleri over the range studied. Non-dormant seeds of improved lines of L. fendleri had better performance at temperatures above 22 °C than did unimproved accessions. Lines of L. fendleri selected for high oil content and salt tolerance had similar temperature requirements for germination except for improved line WCL-LO3, the current line being used in production. This line had optimal temperatures 6 °C higher for germination and growth than the other improved lines. Accessions of L. fendleri collected from elevations above 2000 m performed better at warmer temperatures, whereas those collected from elevations below 2000 m tended to perform better at cooler temperatures. Dormant seeds of L. fendleri germinated more quickly at low temperatures and had lower base (<3 °C) and optimal (22 °C) temperatures than non-dormant seeds (>7 °C and 28 °C, respectively). We speculate that this partial dormancy trait allows populations of L. fendleri to exploit a wider range of temperature conditions in the wild in order to thrive in extreme environments.     

Rice Drying,Storage and Processing: Effects of Post-Harvest Operations on Grain Quality

Various post-harvest processes of rice are commonly employed, especially during the off-season, to ensure its consumption feasibility, which often affect the grain quality. Different forms of drying, storage and processing of rice are evaluated to identify their effects on grain quality. Microwave drying has emerged as an alternative to the widely-used intermittent-drying and fixed-bed-dryer methods of drying paddy rice. Control of drying-air temperatures (between 40 °C and 60 °C) according to the rice variety can improve quality, especially for exotic varieties. Keeping stored grain in hygroscopic balance, with water content between 11% to 15%, at temperatures between 16 °C and 20 °C and with intergranular relative humidity near 60%, allows 12 months of storage in a controlled environment without significant deterioration. Other innovations, notably the application of artificial refrigeration to grain stored in bulk in vertical cylindrical silos and the use of impermeable packaging for storage, ensure the conservation of grain mass. The different stages and equipments used to obtain polished, brown and parboiled rice result in significant changes in the nutritional value of rice because of the removal of the outermost layers of the grains. Polishing reduces the nutritional value and physical homogeneity of rice. Brown rice retains more bioactive compounds and nutrients because it does not lose the outer layer of the grains in the polishing processes. Parboiled rice, although less nutritious than brown rice, has better grain integrity and milling yield and less loss of nutrients than white rice.     

Pig slurry applications to alfalfa: Productivity,solar radiation utilization,N and P removal

A field study was carried out over 4 years at one site in the Low Po Valley, Northern Italy, to examine the effect of various levels of pig slurry applications on alfalfa (Medicago sativa L.) productivity, solar radiation utilization, and nutrient removal. Treatments consisted of three liquid pig manure rates, estimated to provide in total 300, 450 and 600 kg N ha⁻¹ year⁻¹ (PS300, PS450, PS600, respectively), and one unfertilized control (named as Control). Treatments were applied on the second and third year of crop stand (1994 and 1995), whilst during the subsequent fourth and fifth years of crop stand (1996 and 1997) the residual effects of previous treatments were investigated. Regardless of crop age and year-to-year variability, pig slurry tended to increase annual forage production during the 2 years of fertilization and the subsequent biennium of stand duration. Overall, the forage dry matter production, accumulated over four growing seasons and 17 cuts, was 39 000 kg ha⁻¹ for the Control, 44 500 kg ha⁻¹ (+14%) for PS300, to 49 800 kg ha⁻¹ (+28%) for PS450 and 45 800 kg ha⁻¹ (+17%) for PS600. Nitrogen concentration in shoot dry matter was not influenced by the treatment applied. P concentration, on the other hand, was substantially increased by all three rates of pig slurry application, with an evident residual effect observed during the last 2 years of crop stand. However, the evident increase of P availability, assured by pig slurry fertilization, resulted in most of cases in luxury consumption of P by the crop plant. A strong linear relationship was found between cumulative forage dry matter and accumulated incident global solar radiation. Pig slurry fertilization increased significantly the slope of the regressions with respect to the Control. Since enhanced N and P availability may reduce the carbon costs for sustaining root nodules and symbiotic organisms, it seems likely that the crop plant must gain advantage in terms of dry matter produced per unit of radiation intercepted. However, further research is needed to clarify whether the effect of manure is attributable to improved alfalfa efficiency in converting intercepted solar energy into forage dry matter, to enhanced canopy cover thus higher radiation capture per unit of soil area, or to a combination of both mechanisms.     

First results on evaluation of Arundo donax L. clones collected in Southern Italy

The research of alternative crops for biomass production for energy indicates giant reed (Arundo donax L.), widespread spontaneous plant in Mediterranean regions, among the species at high aptitude for accumulation of biomass. Within the activity of an E.U. programme (CEE FAIR CT 97-2028 “Giant reed (A. donax L.) Network. Improvement, productivity and biomass quality”, germplasm of giant reed were collected to evaluate potential production and the phenotypic and genotypic variability, the heritability in order to selecting the best genotypes.In 1997 and 1998, trials were carried out in Primosole site (Piana of Catania, sea level, 37°25′N latitude; 15°30′E longitude), utilizing rhizomes of 39 clones collected in Sicily and Calabria. The rhizomes were transplanted in springtime. Phenological (date of flowering), biometrical (stem density, stem height, number of nodes per stem, diameter and thickness of stems, weight of fresh and dry biomass of leaves, stems and inflorescence) and productive (yield) data were measured. Harvest were carried out in February 1988 and 1989.Yield of 39 clones studied was, in the average, 10.6 t ha⁻¹ of dry matter in the first year and 22.1 t ha⁻¹ in the second one. The clone no. 4 (Piazza Armerina) and the clone no. 20 (Capo d’Orlando) maintained their high productive aptitude in both years; they yielded respectively, 13.1 and 14.1 t ha⁻¹ in the first year and 34.2 and 26.9 t ha⁻¹ in the second one.The yield results positively correlated to stem density, stem weight and plant height. Four characters: biomass yield, stem weight, stem density and stem height showed a significant variance among clones without significant interaction with year. Among the eleven characters measured only yield, stem weight, stem density and stem height had moderate heritability (h²), comprised between 23 and 48% showing promise for genetic improvement.     

Evapotranspiration,yield, and water-use efficiency responses of Lesquerella fendleri at different growth stages

Lesquerella fendleri (Gray) Wats. is a potential new oilseed crop for the arid southwestern United States. Lesquerella seed oil with similar properties as castor oil is being considered as a domestic replacement for the imported castor oil. Development of new crops with low irrigation needs is of high priority. Because the most critical stage of sensitivity to moisture deficits has not been determined in Lesquerella species, the objectives of this study were: (i) to identify the most critical stage or stages for moisture deficit and, (ii) to determine the effect of moisture deficit on yield, yield components, oil and fatty acid composition. Two-year field studies were conducted at the New Mexico State University, Leyendecker Plant Science Research Center. The experimental design was a randomized complete block. The treatments consisted of (a) T1: Continuous favorable soil moisture [irrigated at 50% soil water depletion (SWD)]. (b) T2: Moisture stress (75% SWD) from establishment to initial flowering with no stress from flowering to final harvest (50% SWD). (c) T3: No stress imposed from establishment to initial flowering (50% SWD) followed by stress to final harvest (75% SWD). (d) T4: Moisture stress (75% SWD) from establishment to final harvest. The amount of water applied ranged from 810 to 729 mm for the first year, and 810 to 625 mm for the second year. Seed weight per plant and number of pods per plant were generally higher when water availability was maintained at or above 50% SWD throughout the growing season. Neither seed number per pod nor seed size was influenced by irrigation treatments. Lesquerella was more sensitive to water availability during flowering and seed development as a greater loss in seed yield occurred when irrigation was delayed to 75% SWD during that stage of development. Seed yield and dry matter production from the 2 year field studies were closely related to the seasonal cumulative evapotranspiration. For each millimeter of evapotranspiration, seed yield increased from 1.8 kg ha⁻¹ mm in 1994–1995 to 1.3 kg ha⁻¹ mm for 1995–1996. The dry matter production increased 13.4 kg ha⁻¹ for each mm increase in seasonal evapotranspiration during 1994–1995. This relationship was a second order polynomial with an R² of 0.86 during 1995–1996. The WUE_gr and WUE_dm were highest under the most favorable water availability conditions for growth and seed development. Delaying irrigation to 75% SWD throughout the crop growth period resulted in the lowest oil content. Lesquerolic acid content was not affected by irrigation during both the growing seasons.     

Productivity and residual effects of legumes in rice-based cropping systems in a warm-temperate environment: I. Legume biomass production and N fixation

Field experiments were conducted to investigate the performance of temperate legume species in rice-based cropping systems in a warm-temperate environment in Nepal. Over the period 1994–1996, various legume species were grown during the winter season (October–May) in the Kathmandu valley (27° N, 1350 m asl) with the aim of evaluating their biomass production and N fixation. A wide range of legume species including food, feed and green manure crops proved to be very well adapted to the winter growing conditions in this environment. The cultivation of temperate legume crops therefore, constitutes an alternative to traditional cropping practices such as growing wheat or leaving the land fallow. The temperate species appeared to capitalise on generally favourable growing conditions such as long growing season, low pest and disease pressure, high radiant energy receipt and cool night temperatures. However, performance varied greatly between species and years. Total dry matter yields ranged from 2 to 20 t ha⁻¹ obtained with lentil (Lens culinaris Medic) and bitter lupin (Lupinus mutabilis), respectively. Highest seed yields were produced by fababean (Vicia faba) (5 t ha⁻¹) and field pea (Pisum sativum var. arvense) (3 t ha⁻¹) in the first season. Nitrogen yields and quantities of N fixed ranged from 18 to 481 kg ha⁻¹ and from 0 to 463 kg ha⁻¹, respectively. Large amounts of N were fixed by species such as fababean, Persian clover (Trifolium resupinatum) and bitter lupin. Early sowing in autumn was shown to be beneficial for some crops such as fababean, vetch (Vicia benghalensis) and Persian clover. In these cases, it is, therefore, important to reduce the turn-around interval after rice. Further research is required to fully determine the potential of temperate legume species in these environments with particular emphasis given to the identification of the most adapted cultivars and to reduce the need for irrigation of these winter crops.     

Root growth,soil water content and yield of barley under different tillage systems on two soils in semiarid conditions

An experiment was conducted on two soils in a semiarid area in the Spain’s Ebro valley. Soil A was a Fluventic Xerochrept of 120 cm depth and Soil B was a Lithic Xeric Torriorthent of 30 cm depth. Three tillage systems were compared in Soil A: subsoiler tillage, minimum tillage and no-tillage, and two (minimum tillage and no-tillage) in Soil B. The experiment was repeated for 5 years on Soil A and 3 years on Soil B. Root length density, volumetric water content and dry matter were measured at important developmental stages. Yield was determined at harvest. In Soil A, root length density and volumetric water content were significantly greater for no-tillage than for subsoiler or minimum tillage (up to 1.4 cm cm⁻³ and 5%, respectively), mainly in the upper part of the soil profile. At lower depths, differences as great as 0.8 cm cm⁻³ and 6% were also found. Mean yield (4 years) was similar between no-tillage (3608 kg ha⁻¹) and minimum tillage (3508 kg ha⁻¹), and significantly smaller for subsoiler tillage (3371 kg ha⁻¹). In Soil B, no differences were observed between tillage systems for volumetric water content. Significant interactions between tillage and year were found for root length density, dry matter and yield. Mean yield (3 years) was not significantly different for minimum tillage (1806 kg ha⁻¹) and no-tillage (1867 kg ha⁻¹). The results in Soil A showed that surface conditions are of major importance in the water content of the soil and determined the differences among tillage systems. No-tillage favoured greater and deeper water accumulation in the soil profile and greater root growth. This makes this system potentially better for years of low rainfall. In Soil B no tillage system proved to be better because of the low water-holding capacity of this soil (56 mm).     

Seed quality as affected by nitrogen during true potato seed production and moisture conditions during storage

The objective was to investigate the effects of moisture conditions in storage at 21 C (± 3) on true potato seed (TPS) germination and seedling vigor. The influence of supplemental nitrogen (N) during seed production on these effects was also studied. One set of TPS was stored exposed to ambient humid (> 80% RH) air; the other was stored dry (sealed with silica gel). Germination tests were performed at 7, 11, and 14 months of seed storage. Seedling vigor tests were made at 14, 20, and 23 months. The rate of germination was mostly affected by the moisture conditions during storage. Seed stored dry germinated faster than TPS stored in humid ambient air. The rate of germination increased with time in storage and the percentage of germination was always high (≥ 95%) in dry seed produced with high N. Seedling vigor was mostly affected by N treatments during seed production. High-N seed had a much higher rate and percentage of emergence and seedling dry-weight levels than low-N seed, particularly when stored dry. Seedling vigor criteria decreased with time in storage in low-N seed; in high-N seed, the rate of emergence increased and the percentage of emergence was always high (≥ 95%). In conclusion, the TPS should be produced with high N and stored dry for sowing under unfavorable conditions.     

Model predictions of winter rainfall effects on N dynamics of winter wheat rotation following legume cover crop or fallow

Winter rainfall in a Mediterranean region varies from year to year. Both release of inorganic N from soil organic matter (SOM) or a legume cover crop (LCC) and subsequent nitrate movement in the soil profile are strongly affected by winter rainfall, through its effects on soil water status and on vertical flux. N accumulation of a LCC also varies over years due to weather effects on growth. Thus, these two factors need to be taken into account for efficient use of SOM-N and LCC-N in a wheat (Triticum aestivum L.) rotation. To determine how winter weather might affect the performance of wheat-fallow rotations that include an LCC grown and incorporated during the fallow year, we used the CERES-wheat model and a 46-season weather record to simulate N dynamics of 2-year unfertilized and irrigated winter-LCC wheat systems with high LCC (236 kg N ha⁻¹) or low LCC (118 kg N ha⁻¹) inputs. Unfertilized and fertilized fallow-wheat controls were also simulated. Within a given LCC input value, coefficients of variation for total seasonal N supply (the sum of predicted wheat N uptake, N leaching and inorganic soil N at wheat maturity) over years were <15%, despite the fluctuating winter rainfall (CV 48%). Average N leaching was predicted to be highest in the high LCC input system (108 kg N ha⁻¹), followed by the low LCC input system (86 kg N ha⁻¹) and midseason-intensive and planting-intensive fertilized wheat-fallow systems (82 and 72 kg N ha⁻¹, respectively), and least in the unfertilized wheat-fallow system (54 kg N ha⁻¹). N leaching exceeded 100 kg N ha⁻¹ in 4, 20, 16, 18, and 29 seasons out of 46 seasons, respectively, in the unfertilized and planting-intensive and midseason-intensive fertilized wheat-fallow rotations and in wheat rotations with low and high LCC inputs. There was no difference in predicted wheat yield among the four systems with N inputs from fertilizer or LCC, but yield was lower in the unfertilized wheat-fallow rotation. If the goal of use of LCC was to attain the same yield level as high LCC input or fertilized wheat system while diminishing the risk of N leaching, the low LCC input case met this goal in the short term. However, a simple balance sheet using the model showed that the N balance of the low LCC input system was −147 kg N ha⁻¹ season⁻¹, if we assumed 50% of LCC-N was derived from atmospheric fixation. The low-LCC-input system could therefore fail to maintain inherent soil N fertility in the long term unless nearly 100% LCC-N was derived from fixation.     

Submergence tolerance and yield performance of lowland rice as affected by agronomic management practices in eastern India

Rice is subjected to excessive waterlogging and flash-flooding on large areas in south and south-east Asia. Besides cultivars, submergence tolerance of plants is influenced by various agronomic practices. A field experiment was conducted at Cuttack, India during 1994–1995 to study the effect of method of stand establishment (direct seeding and transplanting), vigour of seed (low and high-density) or seedlings (N-fertilized and unfertilized), plant population (normal and 50% more) and N fertilizer (single basal and split application) on yield performance of lowland rice under conditions of natural submergence and simulated flash-flooding (impounding up to 90 ± 3 cm depth for 10 days at vegetative stage). Flooding reached a maximum depth of 80 cm in 1994 and 52 cm in 1995 under natural submergence. The crop performance was better in 1994 due to timely sowing in dry soil and delayed accumulation of water (43 days after sowing) than in 1995 when sowing was done late in saturated soil followed by early water accumulation (28 days after sowing). Grain yield of rice decreased by 30.0–33.6% due to simulated flash-flooding compared with natural submergence, and by 21.4–33.1% due to transplanting in July compared with direct seeding in May-end/early June. The yield of direct-sown crop increased by using high-density seed of 22.9–23.0 mg weight (5.2–9.0%), higher seed rate of 600 m⁻² (2.2–2.3%) and basal fertilization at 40 kg N ha⁻¹ (19.4–25.7%) compared with low-density seed (19.4–20.1 mg), 400 seed m⁻² and no N, respectively. The yield of transplanted crop increased by using N-fertilized seedlings of 0.49–1.65 g weight (29.5–38.5%), higher number of seedlings at 155 m⁻² (3.5–16.7%) and basal fertilization at 40 kg N ha⁻¹ (31.9–32.5%) compared with unfertilized seedlings (0.19–0.79 g), 115 seedlings m⁻² and no N. Split application of 40 kg N ha⁻¹ — 50% each at basal and top dressing (105–115 days of growth after flash-flooding) — improved yield significantly (10.1–13.1%) over single basal application under simulated flash-flooding, but not under natural submergence conditions. Regression analysis indicated that relative contribution of various factors in increasing grain yield was in order: N fertilizer > seed density > seed m⁻² in direct-sown rice, and N fertilizer > seedlings m⁻² > seedling dry weight in transplanted rice. It was concluded that grain yield of flood-prone lowland rice can be increased by establishing the crop early through direct seeding using high-density seed and basal N fertilization.     

Analysis of cold tolerance in sorghum under controlled environment conditions

Grain sorghum (Sorghum bicolor (L.) Moench) originated in the semi-arid tropics and is generally sensitive to low-temperature stress. Early planting and use of minimum tillage necessitate the development of sorghum hybrids with early season cold tolerance. Genetic variability for cold tolerance exists in sorghum and has been detected by early planting under field conditions and by analysis of seeds and plants under growth chamber conditions. There is limited information on the efficiency of evaluating cold tolerance under growth chamber conditions and the relationship with field performance. The objectives of this study were to quantify the variability of cold tolerance in commercial hybrid seed lots under growth chamber conditions, to exam different components of cold tolerance and their relationships, and to evaluate the consistency of lab test results with data from field tests. Thirty commercial hybrid seed lots were evaluated by growing the entries under 15/10, 13/10, 11/8, and 25/20 °C day/night temperature in a 13/11 h cycle in a growth chamber. Traits measured included emergence percentage, emergence index, shoot and root dry weight, seedling height, and vigor score. Significant genotypic differences were detected for all traits. Correlations among the traits were significant and favorable, which confirmed that simultaneous improvement of these traits should be possible. The same seed lots were also evaluated in a soil-free plate-based assay, in which percent germination, and shoot and root elongation of the seed lots grown in dark at 15 °C were measured. Results from both laboratory tests, soil-based and plate-based, were correlated with data collected in a field study, which was conducted to evaluate cold tolerance of commercial sorghum hybrids at Manhattan, Hesston, Bellville, and Garden City, KS in 1998 and 1999. Single-trait correlations between lab and field studies were significant. Differentiation based on rank-summation index of common traits, rank-summation index correlations and the overlap of best entries, further provided strong support of the efficiency of predicting and identifying elite hybrids using growth chamber assays.     

Maximizing yields in rice–groundnut cropping sequence through integrated nutrient management

Integrated use of organic and inorganic fertilizers can improve crop productivity and sustain soil health and fertility. The present research was conducted to study the effects of application of green manures [sesbania (Sesbania aculeate Poiret) and crotalaria (Crotalaria juncea L.)] and farmyard manure on productivity of rice (Oryza sativa L.) and its residual effects on subsequent groundnut (Arachis hypogaea L.) crop. Rice and groundnut crops were grown in sequence during rainy and post-rainy seasons with and without green manure in combination with different fertilizer and spacing treatments under irrigated conditions. The results showed that application of green manures sesbania and crotalaria at 10 t ha⁻¹ to rice compared to no green manure application significantly increased grain yield of rice by 1.6 and 1.1 t ha⁻¹, and pod yields of groundnut crop succeeding rice by 0.25 and 0.16 t ha⁻¹, respectively. There was no significant difference between the application of crotalaria or farmyard manure at 10 t ha⁻¹ on grain yields of rice, but pod yields of subsequent groundnut crop were greater with application of green manure. There was no significant effect of different spacing 20×15,15×15,15×10 cm² (333 000; 444 000; 666 000 plant ha⁻¹, respectively) on grain yield of rice. Pod yields of groundnut were significantly greater with closer spacing 15×15 cm² (444 000 plants ha⁻¹) as compared to spacing of 30×10 cm² (333 000 plants ha⁻¹). Maximum grain of rice was obtained by application of 120:26:37 kg NPK ha⁻¹ in combination with green manures, whereas maximum pod yield of groundnut was obtained by residual effect of green manure applied to rice and application of 30:26:33 kg NPK ha⁻¹ in combination with gypsum applied to groundnut crop.     

Foliar sprays of concentrated urea at maturity of pigeonpea to induce defoliation and increase its residual benefit to wheat

The pigeonpea (Cajanus cajan (L.) Millsp.) crop retains appreciable amounts of green foliage even after reaching physiological maturity, which if allowed to defoliate, could augment the residual benefit of pigeonpea to the following wheat (Triticum aestivum L.) in a pigeonpea–wheat rotation. The effect of addition of leaves present on mature pigeonpea crop to the soil was examined on the following wheat during the 1999/2000 growing season at Patancheru (17°4′N, 78°2′E) and during the 2001–2003 growing seasons at Modipuram (29°4′N, 77°8′E). At Patancheru, an extra-short-duration pigeonpea cultivar ICPL 88039 was defoliated manually and using foliar sprays of 10% urea (30 kg/ha) and compared with a millet (Pennisetum glaucum (L.) R.Br.) crop, naturally senesced leaf residue and no-leaf residue controls. At Modipuram, the effect of 10% urea spray treatment on mature ICPL 88039 was compared with the unsprayed control. At both locations, the rainy season crops were followed by a wheat cultivar UP 2338 at four nitrogen levels applied in a split plot design, which at Patancheru were 0, 30, 90 and 120 kg N ha⁻¹ and at Modipuram 0, 60, 120 and 180 kg N ha⁻¹. At Patancheru, urea spray added 0.5 t ha⁻¹ of extra leaf litter to the soil within a week without significantly affecting pigeonpea yield. This treatment, however, increased mean wheat yield by 29% from 2.4 t ha⁻¹ in the no-leaf residue pigeonpea or pearl millet plots to 3.1 t ha⁻¹. At Modipuram, the foliar sprays of urea added more leaf litter to the soil than at Patancheru. Here, increase in subsequent wheat yield due to additional pigeonpea leaf litter was 7–8% and net profit 21% more than in the unsprayed control. The addition of pigeonpea leaf litter to the soil resulted in a saving of 40–60 kg N for the following wheat crops in both the environments. The results demonstrated that pigeonpea leaf litter could play an important role in the fertilizer N economy in wheat. The urea spray at maturity of the standing pigeonpea crop significantly improved this contribution in increasing wheat yield, the effect of which was additional to the amount of urea used for inducing defoliation. The practice, if adopted by farmers, may enhance sustainability of wheat production system in an environmentally friendly way, as it could reduce the amount of fertilizer N application to soil and enhance wheat yield.     

Long-term effects of inorganic and organic fertilizer sources on yield and nutrient accumulation of lowland rice

Deceleration in rice (Oryza sativa L.) yield over time under fixed management conditions is a concern for countries like Bangladesh, where rice is the primary source of calories for the human population. Field experiments were conducted from 1990 to 1999 on a Chhiata clay loam soil (Hyperthermic Vertic Endoaquept) in Bangladesh, to determine the effect of different doses of chemical fertilizers alone or in combination with cow dung (CD) and rice husk ash (ash) on yield of lowland rice. Two rice crops—dry season rice (December–May) and wet season rice (July–November) were grown in each year. Six treatments—absolute control (T₁), one-third of recommended fertilizer doses (T₂), two-thirds of recommended fertilizer doses (T₃), full doses of recommended fertilizers (T₄), T₂+5 t CD and 2.5 t ash ha⁻¹ (T₅) and T₃+5 t CD and 2.5 t ash ha⁻¹ (T₆) were compared. The CD and ash were applied on dry season rice only. The 10-year mean grain yield of rice with T₁ was 5.33 t ha⁻¹ per year, while the yield with T₂ was 6.86 t ha⁻¹ per year. Increased fertilizer doses with T₃ increased the grain yield to 8.07 t ha⁻¹ per year, while the application of recommended chemical fertilizer doses (T₄) gave 8.87 t ha⁻¹ per year. The application of CD and ash (T₅ and T₆) increased rice yield by about 1 t ha⁻¹ per year over that obtained with chemical fertilizer alone (T₂ and T₃, respectively). Over 10 years, the grain yield trend with the control plots was negative, but not significantly, both in the dry and wet seasons. Under T₃ through T₆, the yield trend was significantly positive in the dry season, but no significant trend was observed in the wet season. The treatments, which showed positive yield trend, also showed positive total P uptake trend. Positive yield trends were attributed to the increasing P supplying power of the soil.