A monoammónium-foszfát és a diammónium-foszfát hatásának tanulmányozása mikrotenyészedény kísérletben ¹⁵N stabil izotópjelzéssel.
2. A MAP és DAP hatása a talajok N tartalmára, az N formák változásaira.

Latkovics Györgyné¹, Füleky György², Tolner László²

¹MTA Talajtani és Agrokémiai Kutató Intézete, Budapest
²Agrártudományi Egyetem, Talajtani és Agrokémiai Tanszék, Gödöllő, H-2103, Hungary

ABSTRACT

Micro-pot experiments set up to examine the effects of ¹⁵N-labelled mono- and diammonium phosphate gave convincing proof that different N fertilizers increased the dry matter yield of ryegrass and the N quantities taken up the plants to differing extents. The effectiveness of the various N fertilizers was influenced greatly by soil properties. In the present experiment this effect was most obvious on two sandy soils (calcareous sand and sandy brown forest soil with thin interstratified layers of colloid and sesquioxide accumulation), since these gave the lowest values for parameters expressing the efficiency of the N sources. The differences between the effects of the N fertilizers were also greatest on these soils. The effect of DAP was lower than that of the other two N compounds, possibly due to loss of N in the gaseous state.
Soil analyses carried out at the end of the experiment indicated that the total N content of the soils and the quantity of bound NH₄-N rose as a result of treatments. The smallest increase was observed for soils rich in nitrogen, while the greatest increase was recorded for the sandy brown forest soil with thin interstratified layers of colloid and sesquioxide accumulation. Averaged over the soils, the total N quantity increased by 6.7, 7.4 and 6.5 % in the MAP, DAP and ammonium nitrate treatments, respectively.
Averaged over the soils, MAP and DAP resulted in a 16.0 % rise in the bound NH₄-N contents of the soils. This figure was 9.9 % for ammonium nitrate. Compared to the control, the treatments caused the most pronounced increase in the mineral N content of the soils and in the quantities of NO₃-N and exchangeable NH₄-N in the soils, which increased many times. This increase in the two N forms varied according to the soil, being in close correlation with the pH and nitrification of the soil and with environmental aspects of plant N uptake.
The quantities of ¹⁵N fertilizer active agent calculated using the difference method indicate that, with the exception of the two sandy soils, 55.1-63.8 % of the nitrogen introduced onto the soil was identified as surplus nitrogen in the soil or in the plants.
Calculations of ¹⁵N quantities arising from ¹⁵N compounds in the soil and plants show that 69.8 % of MAP nitrogen, 61.4% of ammonium nitrate N and 53.9 % of DAP nitrogen could be demonstrated in the system, though these values varied considerably from one soil to the other. These results draw attention to the importance of N losses in the gaseous state.
The data also indicate that the various types and extents of correlation between N fertilizers and soil properties are closely connected with the transformation of sources into the soil.