The biofertilizers used for rice crops are Azospirillum, phosphobacteria, blue-green algae, Azolla and mycorhizae.
Methods of application of biofertilizers:
Application of Azospirillum Bacteria:
Uses:
Application of Blue-Green Algae:
Blue-green algae (BGA) can also be artificially cultured.
Beds sized 20 x 2 m are prepared in a ploughed land banded on all sides and water is let into the field to a height of 10 cm and maintained at 2–5 cm depth. Then, 5 kg of algal inoculum with 100 g of lime are sprinkled for one cent plot (1 cent = 0.01 acre). After 30 days, without drainage of water, the plot is dried and, hence, an algal mat settles over the soil. Drying, it peels off like flakes and is collected and distributed for rice field application at a rate of 10 kg/ha, 10 days after transplanting.
Otherwise, algal flakes can be powdered, mixed with 25 kg of farmyard manure and 25 kg of soil and can be broadcasted. At the time of application, a thin film of water is to be maintained.
Uses:
Application of Azolla:
Azolla can be multiplied by constructing nurseries with 10 cm deep standing water and adding superphosphate at 8 kg/ha of P2O5 in small plots. Inoculation can be done at 8 kg/m2. Azolla can be used immediately after harvest.
It can be applied as green manure prior to rice planting or can be grown as a dual crop with rice. About 10 tons of fresh Azolla per hectare is equivalent to 30 kg/ha of N.
Uses:
Application of Phosphobacteria:
This is applied at the same dose in the same manner as Azospirillum. Bacteria like Bacillus megatherium var. phosphaticum, Pseudomonas fluorescens, fungi like Pencillium digitatum, Aspergillus niger have been found to have a strong phosphate-dissolving ability.
Uses: 25 to 50 of the recommended phosphorus can be reduced depending upon the native phosphorus content of the soil.
Biofertilizers could offer an opportunity to increase rice yields, productivity and resource use efficiency. Moreover, the increasing availability of biofertilizers in many countries and regions and the sometimes aggressive marketing brings ever more farmers into contact with this technology. However, rice farmers get little advice on biofertilizers and their use from research or extension because so little is known on their usefulness in rice.
The study of Nino Paul Meynard Banayo et al. tested different biofertilizers in an irrigated lowland rice system in the Philippines during four seasons. In all four seasons and across the biofertilizer treatments, the grain yield increased with increasing the amounts of applied biofertilizer. However, this increase was not always statistically significant and the yield increase varied considerably between seasons.
Generally, low yields in that season were due to a typhoon that caused considerable damage through flooding of the experimental field and lodging of the crop. For this reason, the crop was harvested prematurely by about 1 week, which further reduced the attainable yields. The grain yields in the other three experimental seasons were similar. The biofertilizer achieving the highest average grain yields across all four inorganic fertilizer treatments and in all four seasons was BN (Azospirillum lipoferum, A. brasilense). Statistically significant interactions between biofertilizer treatment and inorganic fertilizer treatment could not be detected in any season (at p ≤ 0.05), suggesting that the effect of the biofertilizer was independent of the inorganic fertilizer rate. However, there was a trend towards higher yield increases due to biofertilizer use at low to medium inorganic fertilizer rates. This trend was most obvious for the BN biofertilizer, whereas the performance of the BS (Trichoderma parceramosum, T. pseudokoningii and a UV-irradiated strain of T. harzianum) and BG (rhizobacteria) biofertilizers was less consistent.
The grain yield increase due to biofertilizer use ranged from 200 to 300 kg/ha for the best biofertilizers, when the BN treatment had an almost 800 kg/ha better grain yield than the control. In relative terms, the seasonal yield increase across the fertilizer treatments was between 5% and 18% for the BN biofertilizer, for the BS (Trichoderma parceramosum, T. pseudokoningii and a UV-irradiated strain of T. harzianum) biofertilizer (up to 24% for individual treatment combinations), and between 1% and 9% for the BG (rhizobacteria) biofertilizer (up to 28% for individual treatment combinations). For the calculation of the relative yield increase, only average values could be compared and no statistical analysis could be conducted.
The tested biofertilizers did increase the grain yield significantly, and especially the BN biofertilizer did so consistently. Even in seasons in which no significant effect could be detected due to the yield variability between plots, the grain yield with biofertilizer was usually better than that without it. The seasonal yield increase across fertilizer treatments was between 5% and 18% for the BN biofertilizer, which is within the 5–30% range reported for Azospirillum inoculums and non-rice crops.
Similarly, the observed yield increase for the Trichoderma-based BS (3–13%) was close to the 15–20% rice yield increase described by the trend of yield increases between the different inorganic fertilizer treatments, which was not so clear across seasons but the yield increases were often lower at higher inorganic fertilizer rates. The absolute grain yield increases due to biofertilizer were usually below 0.5 t/ha. The study was conducted to evaluate the effect of different biofertilizers on the grain yield of lowland rice and to investigate possible interaction effects with different inorganic fertilizer amounts.
The results showed significant yield increases for all products tested in some seasons but the most consistent results were achieved by the Azospirillum-based biofertilizer. In most cases, the observed grain yield increases were not huge (0.2 to 0.5 t/ha) but could provide substantial income gains, given the relatively low costs of all biofertilizers tested. The positive effect of the tested biofertilizers was not limited to low rates of inorganic fertilizers and some effect was still observed at grain yields up to 5 t/ha.
However, the trends in our results seem to indicate that the use of biofertilizers might be most helpful in low- to medium-input systems. The results achieved can already be used to specify better advice for farmers on biofertilizer use in lowland rice, but several important questions remain. In particular, biofertilizers need to be evaluated under conditions with abiotic stresses typical for most low- to medium-input systems (e.g. under drought or low soil fertility) and with a range of germplasm because their effect might also depend on the variety used. More upstream-oriented research would be needed to better understand the actual mechanisms involved, which, in turn, could also contribute to making the best use of biofertilizers in rice-based systems.
The study of Achieves of Agronomy and Soil Science testing selected strains of Azotobacter, Acetobacter, Azospirillum and Pseudomonas on two varieties of cotton (American H1098 and Desi HD123) continuously for two years (2000–2001 and 2001–2002) under field conditions. These two varieties of cotton are genetically different. HD123 is a Desi cotton variety, which is diploid, with less nutrient uptake and lower susceptibility to pests. H1098 is a tetraploid American cotton variety, which has high nutrient uptake ability and is highly susceptible to pests.
As cotton is a summer crop and the temperature in the summer rises up to 48 °C, the selected cultures were mostly high temperature tolerant. Azotobacter has the property of forming cysts. This enables it to survive at high temperatures. Several reports have suggested that PGPRs (plant-growth-promoting rhizobacteria) also stimulate plant growth by facilitating the uptake of minerals such as N, P, K and other important micronutrients (Barea et al., 1976; Dobbelaere et al., 2003). This uptake is suggested to be due to a general increase in the volume of the root system. Higher amounts of IAA effect the seed emergence of wheat primarily because of the production of growth regulators by bacteria.
Better performance is attributed to the high temperature tolerance of some cultures during the cotton crop season. It is also due to the better proliferation, survival, ability to fix more nitrogen, antifungal properties of the inoculant strains and growth-promoting substances which are also likely to contribute to the beneficial effects on crops. The Azotobacter strains used in this investigation have also been tested for the above-mentioned properties and it has been observed that they have the ability to excrete ammonia, produce IAA, siderophores, have antifungal properties and are capable of fixing nitrogen.
Higher seed yield, plant growth and survival of the bio-inoculants may be attributed to many factors, most important being the favourable influence exerted by root exudates, which contain acids, organic acids, carbohydrates and growth hormones like indole acetic acid. IAA synthesized by bacteria is taken up by the plants and can stimulate cell proliferation. Nitrogen fixation and solubilization of insoluble phosphate also contribute significantly to plant growth. Phosphate solubilizers can exert considerable influence on nutrient uptake.
Therefore, the use of phosphate-solubilizing, IAA-producing Azotobacter chroococcum may augment the efficiency of applied and native P2O5 by reducing fixation by the soil fraction. Therefore, selection of isolates with high temperature tolerance, phosphate solubilization, phytohormone production and high nitrogen fixation has expanded the possibilities of applying free-living nitrogen fixers to cereals and other non-legume crops. Our studies suggest that microbial inoculants can be used as an economic input to increase crop productivity and lower the fertilizer level along with harvesting more nutrients from the soil. However, a lot of research work is still left to be done on aspects of phytohormone production and increased nutrient uptake, which is an important parameter in plant–microbe interactions.
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