Surya P. Bhattarai

Oxygation Unlocks Yield Potentials of Crops in Oxygen‐Limited Soil Environments

Subsurface drip irrigation (SDI) offers well‐documented potential for improving water use efficiency in irrigated agriculture. However, SDI in common with other forms of irrigation is liable to exclude soil air (and therefore oxygen) around the root zone during and following irrigation events, thus reducing root function and crop performance. When SDI is practiced with oxygation (i.e., aerating the rhizosphere by way of the irrigation stream) it could transform the irrigation industry, for it provides a source of oxygen in a root environment that suffers from temporal hypoxia, and occasionally from anoxia. The oxygen is introduced into the irrigation stream by way of the venturi principle, or with solutions of hydrogen peroxide. Oxygation assures optimal root function, microbial activity, and mineral transformations, and leads to enhanced yield and water use efficiency under hypoxic conditions. It also improves plant performance and yield under irrigated conditions previously considered to be satisfactory for crop growth, and offers scope to offset some of the negative impacts of compaction and salinity, related to poor soil aeration, on crop growth. Representing minimal capital investment and recurrent costs, economic returns appear very favorable, as do associated benefits to the environment, measured as reduced drainage, containment of rising water tables, better nutrient use efficiency, and reduced demand by agriculture for irrigation water. The aeration status of irrigated soils deserves more attention than it has received in the past if we wish to unlock yield potential constrained by soil oxygen limitations and effect the yield increases essential to keeping pace with future food (and fibre) demand.

Oxygation enhances growth, gas exchange and salt tolerance of vegetable soybean and cotton in a saline vertisol.

Impacts of salinity become severe when the soil is deficient in oxygen. Oxygation (using aerated water for subsurface drip irrigation of crop) could minimize the impact of salinity on plants under oxygen-limiting soil environments. Pot experiments were conducted to evaluate the effects of oxygation (12% air volume/volume of water) on vegetable soybean (moderately salt tolerant) and cotton (salt tolerant) in a salinized vertisol at 2, 8, 14, 20 dS/m EC(e). In vegetable soybean, oxygation increased above ground biomass yield and water use efficiency (WUE) by 13% and 22%, respectively, compared with the control. Higher yield with oxygation was accompanied by greater plant height and stem diameter and reduced specific leaf area and leaf Na+ and Cl- concentrations. In cotton, oxygation increased lint yield and WUE by 18% and 16%, respectively, compared with the control, and was accompanied by greater canopy light interception, plant height and stem diameter. Oxygation also led to a greater rate of photosynthesis, higher relative water content in the leaf, reduced crop water stress index and lower leaf water potential. It did not, however, affect leaf Na+ or Cl- concentration. Oxygation invariably increased, whereas salinity reduced the K+ : Na+ ratio in the leaves of both species. Oxygation improved yield and WUE performance of salt tolerant and moderately tolerant crops under saline soil environments, and this may have a significant impact for irrigated agriculture where saline soils pose constraints to crop production.

Effects of subsurface drip irrigation rates and furrow irrigation for cotton grown on a vertisol on off-site movement of sediments, nutrients and pesticides

Subsurface drip irrigation can reduce off-farm movements of fertilizers and pollutants and improve the water use efficiency of irrigated agriculture. Here we compared the effects of furrow and subsurface drip at different irrigation rates, based on a percentage of daily crop-evapotranspiration rates (ETc), on run-off and off-site movement of suspended sediment, nutrients and pesticides from cotton crops grown on a vertisol. Our results show that furrow irrigation significantly increased suspended soil loss, of 5.26 t ha−1, compared to that of subsurface drip irrigation at 120% of ETc, of 2.53 tha−1, whereas no erosion was recorded with deficit subsurface drip irrigation. Off-site movement of nitrogen in furrow, of 18.63 kg ha−1, was five times greater than subsurface drip irrigation at 120% ETc. It was much less with 105% ETc (0.37 kg ha−1) and 90% ETc (0.15 kg ha−1), and absent for 75% and 50% of ETc. Phosphorus loss from furrow, of 778 g ha−1, was greater than for the wetter subsurface drip treatments that gave 23 gha−1 for 90% ETc and 19 gha−1 for 120% ETc. No P loss was recorded from drier subsurface drip irrigation rates. Herbicides such as atrazine and diuron were applied in the year prior to the experiment, but considerable amounts were recorded in furrow run-off in both years, but only at 90 and 120% ETc subsurface drip irrigation in the first year. Concentrations of applied herbicide residues in the runoff exceeded the minimum threshold level for 99% species protection and, although the total amount of herbicide movement was higher in furrow, at times the concentration was greater for wetter subsurface drip irrigation run-off. Residues of insecticides, such as endosulphan applied in a previous year and dimethoate applied in the current years, were recorded in runoff from subsurface drip at 120% and furrow irrigation. Their concentrations in each year exceeded minimum threshold level. Subsurface drip irrigation at 75% ETc offered the best trade-off between off-site run-off, erosion and pesticide movement and yield and water use efficiency.

The Response of cotton to subsurface drip and furrow irrigation in a vertisol

The practice and management of subsurface drip irrigation (SDI) on heavy clay soils is poorly understood. Over-irrigation can lead to excessive runoff and drainage, with associated negative environmental consequences. Experiments were conducted in 2001/2002 and 2002/2003 on cotton (Gossypium hirsutum) in a Vertisol in Australia to evaluate the effect of SDI at various application rates on cotton yield and quality, and the results were compared with those for conventional furrow irrigation. Irrigating with SDI that supplied 50 % or 75 % of daily crop evapotranspiration (ETc) maintained a dry upper soil profile throughout the season. SDI at 50 % ETc could potentially capture 250 mm more rain during the season compared to SDI 90 % ETc, and even more than furrow irrigation. However, supplying only 50 % ETc with SDI hastened the maturity of the crop by on average 25 days compared with furrow irrigation and higher SDI rates, fewer bolls were set and yields were lower than in the other treatments. Nevertheless, a shorter season, if yield sacrifice is acceptable, favours logistics when integrating winter crops with summer cotton. It also reduces the number and cost of pesticide sprays and irrigation. Yield plateaued when 75 % or more of daily ETc was supplied by SDI. The two drier treatments (SDI at 50 % and 75 % of ETc) had consistently higher water use efficiencies (WUE) for lint production compared with those of the two wetter SDI treatments (SDI at 90 % and 105/120 % ETc). All SDI treatments were also more efficient in the first year in the use of water for lint production than was furrow irrigation, but improved irrigation management in the form of faster irrigation and reduction of tail water in the second year obviated the advantage of SDI. Irrigation of cotton with SDI at 75 % ETc offered significant benefits in terms of saved irrigation water over wetter SDI treatments, resulted in the highest average WUE for lint production over the two years, and reduced drainage and runoff compared with higher SDI rates and furrow irrigation.

Biochar, Bentonite and Zeolite Supplemented Feeding of Layer Chickens Alters Intestinal Microbiota and Reduces Campylobacter Load

A range of feed supplements, including antibiotics, have been commonly used in poultry production to improve health and productivity. Alternative methods are needed to suppress pathogen loads and maintain productivity. As an alternative to antibiotics use, we investigated the ability of biochar, bentonite and zeolite as separate 4% feed additives, to selectively remove pathogens without reducing microbial richness and diversity in the gut. Neither biochar, bentonite nor zeolite made any significant alterations to the overall richness and diversity of intestinal bacterial community. However, reduction of some bacterial species, including some potential pathogens was detected. The microbiota of bentonite fed animals were lacking all members of the order Campylobacterales. Specifically, the following operational taxonomic units (OTUs) were absent: an OTU 100% identical to Campylobacter jejuni; an OTU 99% identical to Helicobacter pullorum; multiple Gallibacterium anatis (>97%) related OTUs; Bacteroides dorei (99%) and Clostridium aldenense (95%) related OTUs. Biochar and zeolite treatments had similar but milder effects compared to bentonite. Zeolite amended feed was also associated with significant reduction in the phylum Proteobacteria. All three additives showed potential for the control of major poultry zoonotic pathogens.

Effect of industrial hemp (Cannabis sativa L) planting density on weed suppression, crop growth, physiological responses, and fibre yield in the subtropics

Abstract Population density of industrial hemp (Cannabis sativa L.) in the field influences crop growth habit, fibre yield and quality. Therefore, optimization of plant population density is required to control growth and

Benefits of oxygation of subsurface drip-irrigation water for cotton in a Vertosol

Abstract. Australian cotton (Gossypium hirsutum L.) is predominantly grown on heavy clay soils (Vertosols). Cotton grown on Vertosols often experiences episodes of low oxygen concentration in the root-zone, particularly after irrigation events. In subsurface drip-irrigation (SDI), cotton receives frequent irrigation and sustained wetting fronts are developed in the rhizosphere. This can lead to poor soil diffusion of oxygen, causing temporal and spatial hypoxia. As cotton is sensitive to waterlogging, exposure to this condition can result in a significant yield penalty. Use of aerated water for drip irrigation (‘oxygation’) can ameliorate hypoxia in the wetting front and, therefore, overcome the negative effects of poor soil aeration. The efficacy of oxygation, delivered via SDI to broadacre cotton, was evaluated over seven seasons (2005–06 to 2012–13). Oxygation of irrigation water by Mazzei air-injector produced significantly (P < 0.001) higher yields (200.3 v. 182.7 g m–2) and water-use efficiencies. Averaged over seven years, the yield and gross production water-use index of oxygated cotton exceeded that of the control by 10% and 7%, respectively. The improvements in yields and water-use efficiency in response to oxygation could be ascribed to greater root development and increased light interception by the crop canopies, contributing to enhanced crop physiological performance by ameliorating exposure to hypoxia. Oxygation of SDI contributed to improvements in both yields and water-use efficiency, which may contribute to greater economic feasibility of SDI for broadacre cotton production in Vertosols.

Review of Flowering Control in Industrial Hemp

Hemp (Cannabis sativa L.) is a dioecious annual that commences its reproductive cycle when photoperiods are shorter than a critical length. Photoperiod-sensitive varieties grown in low latitudes with short-day lengths tend to produce early flowering, short plants affecting the yield and quality of the fiber. The photoperiodic sensitivity of the crop could be controlled by the activation or deactivation of genes triggered by the change in light duration perceived by photoreceptive pigments. The sexual dimorphism of Cannabis is genetically determined by the XY chromosomal mechanism although sexual morphology is primarily a result of endogenous plant growth regulator levels that fluctuate in response to environmental variables. Occurrence of occasional hermaphroditic flowers and monoecious plants are probably the result of these fluctuations. Understanding the mechanisms of photoperiodicity and sexual inheritance contributes to advances in breeding and crop management that may underpin the expansion of the commercial cultivation of the crop in nontraditional agroecological domains.

Zeolite food supplementation reduces abundance of enterobacteria

According to the World Health Organisation, antibiotics are rapidly losing potency in every country of the world. Poultry are currently perceived as a major source of pathogens and antimicrobial resistance. There is an urgent need for new and natural ways to control pathogens in poultry and humans alike. Porous, cation rich, aluminosilicate minerals, zeolites can be used as a feed additive in poultry rations, demonstrating multiple productivity benefits. Next generation sequencing of the 16S rRNA marker gene was used to phylogenetically characterize the fecal microbiota and thus investigate the ability and dose dependency of zeolite in terms of anti-pathogenic effects. A natural zeolite was used as a feed additive in laying hens at 1, 2, and 4% w/w for a 23 week period. At the end of this period cloacal swabs were collected to sample faecal microbial communities. A significant reduction in carriage of bacteria within the phylum Proteobacteria, especially in members of the pathogen-rich family Enterobacteriaceae, was noted across all three concentrations of zeolite. Zeolite supplementation of feed resulted in a reduction in the carriage of a number of poultry pathogens without disturbing beneficial bacteria. This effect was, in some phylotypes, correlated with the zeolite concentration. This result is relevant to zeolite feeding in other animal production systems, and for human pathogenesis.

The Effects of Different Sowing Times on Maturity Rates, Biomass, and Plant Growth of Industrial Fiber Hemp

Hemp in the Northern hemisphere is planted in April–May under long-day conditions to prevent precocious flowering. In Queensland, Australia, where premature flowering is inevitable, it may be necessary to plant hemp closer to the summer solstice to optimize solar radiation and longer day-length. However, high temperature at that time may limit growth of hemp in the Burnett/Wide Bay region, Queensland, Australia. Field experiment where day length did not exceed 13 h and 40 min, we evaluated effect of five spring/summer sowing times on flowering time, plant growth and yield. Of the five planting dates (15 Sept–PD1, 25 Oct–PD2, 25 Nov–PD3, 16 Dec–PD4, and 23 Jan–PD5), (PD3) stood out as the optimal time of planting. Planting date 3 was significantly later to develop male buds and the first open male flowers. Plant height at harvest was the highest for PD3 (999 mm) compared to all other planting dates. Planting date 3 also yielded highest dry matter (7.8 t ha−1). Yields were well below what would be considered viable in Europe for fiber hemp, but the results of the experiment may be used to indicate potential of seed hemp crop for QLD.