CO 2 evolution and chemical constituents of leaves and tubers of potato plants as influenced by organic compost and mineral N-fertilizers applied individually or in different combination rates along with seaweed extract

In field trials carried out during the two successive summer growing seasons of 2008 and 2009 at the experimental farm of the Fac. Agric. , Shebin El-Kome, Minoufiya Univ., Egypt. Potato plants of the cv. Nieta were grown under several Nfertilization regimes, which used at the recommended dose of 120 kg N/fed. as soil addition. Nfertilizers were applied as zoological or botanical compost comparing to inorganic N-fertilizer either individually or in different combination rates along with foliar spray with seaweed extract to examine their effects on CO2 production in the rhizospheric root zone and chemical constituents of leaves and tubers of potato plants. Carbon dioxide production, which is a direct indicator of microbial communities and activities as well as soil enzyme activities, plays an important role in maintaining soil fertility. The results indicated that fertilization with any of the used organic fertilizers namely zoological or botanical compost either each alone or in different combination rates with chemical fertilizer increased significantly CO2 production with more effectiveness for the application of fertilizer mixture of 25 % mineral N + 75 % zoological compost + foliar spray of seaweed extract followed by 50 % mineral N + 50 % zoological compost + foliar spray of seaweed extract then 50 % mineral N + 50 % botanical compost + foliar spray of seaweed extract comparing with unfertilized control and mineral fertilized treatment. All investigated treatments significantly enhanced chlorophyll a, b and total chlorophyll content comparing with check treatment, however the three above-named treatments in descending order gave the highest content of chlorophyll pigments in potato leaves. NPK uptake by potato plants and total carbohydrates accumulation tended to increase significantly as a sequence of the tested organic and inorganic N fertilizers either in individual form or in different combination rates from each compared to the unfertilized treatment control. The greatest values of NPK and total carbohydrates were occurred also in leaves of potato plants fertilized with the above-said treatments. It is worthy to mention that unfertilized control, both organic fertilizers, each of them as a sole source of N, namely 100 % zoological compost and 100 % botanical compost as well as foliar spray with seaweed extract recorded the lowest nitrate accumulation in leaves and tubers of potato plants comparing with mineral fertilization treatment (100 % mineral N), which exerted the highest values of it. The less nitrate content was detected due to using 25 % mineral N + 75 % zoological compost + foliar spray of seaweed extract followed by 50 % mineral N + 50 % zoological compost + foliar spray of seaweed extract then 50 % mineral N + 50 % botanical compost + foliar spray of seaweed extract. Tubers of the plants fed only with organic compost either as zoological or botanical form (100 % zoological compost and (100 % botanical compost), respectively contain the lowest levels of reducing sugars, whereas unfertilized control followed by foliar spray with seaweed extract exerted the highest values, respectively. Concerning to non-reducing and total sugars content in potato tubers, the application 25 % mineral N + 75 % zoological compost + foliar spray of seaweed extract followed by 50 % mineral N + 50 % zoological compost + foliar spray of seaweed extract then 50 % mineral N + 50 % botanical compost + foliar spray of seaweed extract exhibited the highest values of the above-cited compounds, however the lowest ones were occurred in tubers of unfertilized control plants. Starch and total crude protein contents increased significantly by the application of the all studied fertilization treatments compared with the unfertilized control, whereas the greatest values from starch and total protein were recorded in tubers of plants received the fertilization mixture of 25 % mineral N + 75 % zoological compost + foliar spray of seaweed extract followed by 50 % mineral N + 50 % zoological compost + foliar spray of seaweed extract then 50 % mineral N + 50 % botanical compost + foliar spray of seaweed extract. Kew words: Potato, CO2 evolution, organic compost , mineral N-fertilizers, seaweed extract, chemical constituents.