Nitrogen and phosphorus soil-test calibration studies in the Chaouia region of Morocco.
1988
Soltanpour P.N. | El Gharous M. | Azzaoui A. | Abdelmonem M.
A series of on-farm factorial N and P studies for use in soil test calibration were initiated in the fall of 1985 to determine the critical level of NaHCO3-extractable P for wheat crops grown in soils of the Chaouia region in the province of Settat, Morocco; the effect of previous crop, yield level, initial soil nitrate, and N mineralization potential on the N requirement of wheat crops grown in the region; and the efficiency of banding as compared with broadcasting superphosphate. Three different soil types were selected based on their potential productivity, namely shallow (rendolls), moderately deep (calcixerolls), and deep (chromoxererts and their intergrades). The previous crops were wheat or barley and legumes in all soils, weedy fallow in shallow soils, and corn in deep soils. The details of experimental methods are given elsewhere (Soltanpour 1987). No interaction between applied N and P fertilizers on the yield of wheat was observed. In 1985-86, rainfall was 300 mm with an excellent distribution. In 1986-87, rainfall was 200 mm for calcixeroll and chromoxerert sites and 240 mm for the rendoll site. The distribution in the later year was poor. The results showed that for rendolls no nitrogen fertilization was required when wheat followed a legume crop or weedy fallow, but about 30 kg/ha was required after cereals. In these shallow soils, N uptake or yield was not related to residual soil NO3-N, probably because of variability in soil depth or other factors. Nitrogen uptake in check plots was well correlated with soil NO3-N in 20-, 40-, and 60-cm profiles of calcixerolls and chromoxererts indicating the importance of a NO3-N soil test. Relative yield was a linear function of nitrate content in the soil profile. For a grain yield of 2 t/ha, 18, 31, and 50 kg NO3-N/ha was required in 0-20, 0-40, and 0-60 cm profiles. An N model based on critical level of NO3-N in the profile, soil NO3-N, apparent efficiencies of fertilizer N and soil NO3-N yield goal and previous crop was developed and will be verified under farmers' conditions of management.
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