Effect of the inorganic soil nitrogen level on fertilizer nitrogen requirements by spring barley grown on regularly manured soils
1990
Mattsson, L. (Sveriges Lantbruksuniv., Uppsala (Sweden). Inst. foer Markvetenskap)
In a series with 39 annual field experiments during the years 1982-1985 the effects of the level of soil mineral N down to 90 cm depth on fertilizer N responses in barley were investigated. Rates of N corresponding to 0, 30, 60, 90, 120, 150 and 180 kg ha-1 in Nitro chalk were broadcast prior to sowing. The experimental sites were distributed all over Sweden and were situated on fields that commonly received manure in the rotation. A significant correlation between the increase in grain yield and content of soil mineral N was demonstrated. A multiple linear regression model including a linear and a quadratic effect of fertilizer N and an interaction between soil mineral N and fertilizer N explained 64% of the variation between sites. Economical optimum rates of fertilizer N were calculated to be reduced or increased by 0.73 kg ha-1 as the soil mineral N within 0-90 cm depth increased or decreased by 1 kg ha-1. In spite of the significant effects, a considerable variation in the relationships were observed for soil mineral N values in the interval 20-100 kg ha-1. This makes the fertilizer predictions uncertain. The possibility of more accurate fertilizer predictions when soil mineral N values are high were discussed. Primarily, analysis of soil mineral N should be performed when high values are to be expected.
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