In North Dakota, adoption of conservation tillage practices has resulted in an accumulation of crop residue remaining on the soil surface. North Dakota producers receive a nitrogen credit for long-term no-till but due to previous crop residue this credit may not be realistic for providing partial nutrient needs to subsequent crops in a cool environment with a short growing season. Our objectives were to evaluate the N mineralization potential of common crop residues to determine whether crop residue accumulation in no-till systems can provide sufficient nitrogen quantities needed for subsequent crops. Three lab incubation studies were conducted to provide N mineralization insights for individual crop residues, crop residues over several simulated growing seasons, and crop residue in diversified cropping systems. Differences in soil texture, surface application versus incorporation of residue, freeze and thaw cycles and combinations of residues were all factors examined. Results indicated that crop residue decomposition and N release from the residue treatments generally immobilized N but were not significantly different from the bare soil for nearly all studies. The only exception observed was for the forage radish cover crop which showed the potential to improve soil N mineralization in select three-year rotations. Findings of these studies show that most wide C:N ratio crop residues will immobilize soil N in a no-till system under ideal conditions (i.e. moisture, temperature, and residue particle size). These findings suggestion that a fertilizer N credits may require reevaluation and take into consideration soil moisture with validated data to support the fertilizer N credit.

A greenhouse pot study was conducted on three soils with varying clay contents to establish K critical value at -3 and -1/3 bar soil moisture levels. Four K fertilizer treatments (0, 0.07, 0.14, and 0.3 g/pot) replicated three times were arranged in a complete randomized block design. The Cate-Nelson graphical procedure revealed that K critical values for corn and soybeans were not equal at the two designated moisture levels. The corresponding percentage yield however was higher at -1/3 bars for corn and at -3 bars for soybean. Statistical regression analysis showed that there was a minor response in plant tissue K to changes in soil test K at both soil moisture levels. The ANOVA at 0.05 significance level showed the observed data were consistent with the null hypothesis that there was no significant difference between plant percentage yield and the increasing K fertilizer application rates at the two moisture levels.