P Demyttenaere

Spatial variability of n fertilizer application and wheat yield

The spatial distribution of two N fertilizer applications (one liquid and one solid) and the yield of winter wheat of a 1 ha field was analyzed at 247 locations. The N fertilizations, as well as their sum, were lognormally distributed, the grain yield showed a normal frequency distribution. Bidirectional semivariograms of all data sets indicated no range of autocorrelation. As a consequence, all data within each set could be considered as being spatially independent for distances larger than the smallest sampling spacing (2.5 m). The semivariograms of the fertilizer applications showed an anisotropic behavior with the largest variability perpendicular to the direction of movement of the spreader. This was caused by strips which had received less, or more, N fertilizer than the intended rate. On the other hand, the theoretical model of the semivariogram of the grain yield could be considered to be an isotropic pure nugget effect, indicating a high degree of spatial homogeneity. This homogeneity results from a yield decline whenever less as well as more than the maximum fertilizer amount was given, as could be concluded out of the yield response curve. The latter, constructed with all 247 measurements, allowed the calculation of the yield loss due to an uneven N fertilizer spreading: 71 kg grain ha−1 at P = 0.09. The number of samples required to estimate the mean value of the N fertilizations and grain yield with a probability of 95% and a precision of 5% was 153, 65 and 9 for the liquid fertilization, the solid fertilization and the grain yield, respectively. These samples could best be located randomly within the field.

Comparison of row and broadcast N application on N efficiency and yield of potatoes

A small rooting depth, a poor root distribution and an inefficient fertilizer application by broadcasting N fertilizers on potatoes result in a restricted N efficiency. Therefore, an application of N fertilizers in the row has potential possibilities to enhance this N efficiency.

Causes and consequences of differences in latent mineral nitrogen residues in the soil profile.

Abstract The latent mineral‐N residue is the smallest required inorganic nitrogen quantity, at the moment that the maximum N‐amount is present in the crop, to obtain optimum yields. These latent mineral‐N residues vary widely between crops, ranging from 25 kg NO3‐N/ha, for cereals and sugar beet, upto more than 100 kg NO3‐N/ha for some leaf vegetables. Different factors are responsible for these variations. For potatoes and some vegetables, a restricted root intensity and distribution result in high latent mineral‐N residues. As a consequence of a shallow rooting pattern, high NO3‐N residues can be found below the rooting zone. For blanching celery, mineral‐N residues of the order of about 200 kg N03‐N/ha between 60 and 120 cm depth are commonly found. Differences in N‐demand near to harvest time are also responsible for variations in latent mineral‐N residues. Due to a low N‐demand at the end of the growing season, low mineral‐N residues are advised for winter cereals and sugar beet. On the contrary, to ...