Nitrogen Recovery in Single- and Multiple-harvested Direct-seeded Broccoli Trials

Abstract

Abstract Broccoli ( Brassica olerica L. var. italica ) and corn ( Zea mays L.) N-treated adjacent plots had essentially the same initial Ν content. Extractable inorganic Ν to a depth of 60 cm (N at 28 to 48 kg·ha -1 ) was considerably less than the Ν taken up into the total above-ground parts of the crop (N at 118 to 157 kg·ha -1 ); thus, both crops depended on mineralization of soil Ν for their growth. Although broccoli and corn had the same total demand for Ν as shown by total uptake, only broccoli responded to Ν application. Since corn required Ν over a longer period of time (116 days) than broccoli (90 days), the net mineralization rate of soil Ν [0.8 to 1.0 kg·ha -1 (per day)] matched approximately the average Ν uptake rate over the whole season [1.1 to 1.2 kg·ha -1 (per day)] in the corn trial. Net Ν mineralization rate [-0.1 to 1.4 kg·ha -1 (per day)] tended to be less than the average Ν uptake rate by broccoli (1.3 to 3.1 kg·ha -1 (per day)], resulting in the response to Ν applied. Slightly more downward movement of inorganic Ν occurred in the 1982 than in the 1979 broccoli trial. This coincided with slightly higher precipitation in 1982 particularly late in the growing season. By using path coefficient analyses, it was found that several plant variables were consistently correlated with horticultural yield, but the nature of the relationship was not consistent from year to year, suggesting that slightly different mechanisms contributed to the yield effect each year but that the net result was similar.