Soil properties and nutrient uptake by rice under different fertigation regimes in rice based cropping systems
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Date
2017-07
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Department of Soil Science & Agricultural Chemistry, BAU, Sabour
Abstract
Nutrient and water management are important for diversifying and intensifying the rainfed rice based cropping systems. A fertigation experiment in split plot design was laid out at the farm of BAC, Sabour in 2014 with three levels of fertigation in main plots (nitrogen levels as fertigation @ 20, 40, and 60 kg ha-1 in rice and irrigation levels @ 200, 300 and 400 mm in post rice crops) and four rice based cropping systems as sub plot treatments (rice followed by either durum wheat, barley, lentil or chickpea). The third year rice crop in the system was used for taking observations on growth and yield, soil physical and chemical parameters and nutrient uptake in terms of N, P and K using standard methods. Fertigation levels and cropping systems can be significant determinants of crop yields. They also have distinct influences on soil conditions and nutrient relations. Most of the significant influences are cyclic, being observable only during a part of the year. Rice grain yield was significantly greater under higher fertigation regimes. Steady state infiltration rate was found higher under rice-legume cropping systems in comparison to any of the rice-cereal cropping systems (i.e. rice-durum wheat and rice-barley) but no influences of fertigation and cropping systems on bulk density were observable. Fertigation regimes and cropping systems can influence the profile penetration resistance.
Maximum water holding capacity of surface soil after the harvest of rabi season crops was significantly greater under the higher fertigation regimes. Soil organic carbon was reduced in rice legume cropping systems, likely because of greater rate of organic matter decomposition under higher nitrogen fixation as well as due to the effect of heterotrophic Rhizobia colonising the legume roots. Nitrogen availability at the start of the rice growing season aka. left over available nitrogen by the rabi season crops in the sub-soil layers was significantly greater in treatments receiving less irrigation during the rabi season. Cropping systems influenced the availability of nitrogen in the soil after rice harvest as a result of differential nitrogen applications and contributions of the preceding crops and followed the trend rice-chickpea < rice - durum wheat < rice-barley = rice-lentil cropping systems. The available nitrogen content in the 15-30 cm and 30-45 cm soil layer was also significantly lower in rice-chickpea cropping system in comparison to other cropping systems.
Before rice crop establishment, the average P availability in the surface soil and at the depth of 15-30 cm in the soil followed the trend rice-lentil > rice-chickpea > rice-durum wheat = rice-barley cropping systems. At the depth of 30-45 cm, rice barley cropping system exhibited statistically lower availability of P in comparison to other cropping systems. This again shows the probable effect of heterotrophic Rhizobia, which act as phosphate solubilizers while consuming soil available nitrogen in decomposing organic matter. Available K was found to be statistically similar across various fertigation regimes and cropping systems.
N fertigation @ 60 kg ha-1 and 40 kg ha-1 demonstrated significantly greater nitrogen uptake by rice grains in comparison to 20 kg ha-1, which is due to significantly greater rice grain yield under these treatments. P content in rice straw was found to be lower with 40 kg ha-1 and 60 kg ha-1 N fertigation compared to 20 kg ha-1 N fertigation because of the dilution effect under greater N application. P uptake by rice grains was significantly greater in rice-lentil and rice-durum wheat cropping systems in comparison to rice-chickpea and rice-barley cropping systems which probably is the result varying rates of P addition and extraction resulting in greater P availability in certain treatments at the start of the season.
K content in rice straw was found to be significantly more in rice- durum wheat cropping system compared to rest three cropping systems. This resulted in low K availability after harvesting of rice in rice -durum wheat cropping system than other cropping systems. K content in rice straw was greater in rice-durum wheat cropping system because of greater application of potassic fertilizer (MOP) cumulated over both rabi and kharif seasons. A significant effect of cropping systems on the internal nutrient use efficiency of P was observed as rice-barley cropping system had significantly greater internal phosphorus use efficiency than the other three cropping systems. The partial factor productivity of applied nutrients was significantly affected by fertigation regimes in case of N, P and K as N fertigation had a negative relation with the partial factor productivity of applied nitrogen but a positive relationship with the partial factor productivity of applied P and K. The phosphorus harvest index was significantly greater when N fertigation was given @ 40 kg ha-1 in comparison to when N fertigation rates were 20 and 60 kg ha-1. Phosphorus harvest index was significantly lower for rice-durum wheat and significantly greater for rice-lentil cropping system in comparison to other systems. The physiological phosphorus and potassium use efficiencies of rice were significantly higher under higher levels of N fertigation.
An analysis of the salient findings and reasoning based on pre-existing literature lead us to the conclusion that fertigation and cropping systems do have significant influences on productivity of rice based cropping systems along with soil physical conditions and nutrient relations in soils and plants. These influences might have resulted from the interactive effects of diverse microbial communities acting under the differential nutrient additions and removals as well as soil profile moisture conditions influencing the root growth, exudation, and decomposition created by the imposed treatments. Most of the influences are not long lasting but their ephemeral nature can be an indicator of the direction of changes expected in the long term. Hence, the decision of fertigation in rainfed rice based ecologies should not only take into consideration the objectives of efficient water and nutrient delivery but also the ecosystem characteristics on a cropping systems basis.
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