Corn response to phosphorus, sulfur and potassium fertilization

Flavio H. Gutiérrez Boem1, Gustavo Ferraris2, Pablo Prystupa1 and Fernando Salvagiotti3
1 College of Agronomy, University of Buenos Aires, Av. San Martín 4453, (1417) Buenos Aires, Argentina, Ph. 54-11-4524-8076
2 National Institute of Agricultural Technology (INTA), EEA Oliveros, Ruta 11 km 353, (2206) Oliveros, Santa Fe, Argentina, Ph. 54-3476-498010
3 National Institute of Agricultural Technology (INTA), EEA Pergamino, CC31, (2700) Pergamino, Buenos Aires, Argentina, Ph. 54-2477-431250

Justification
Early works have shown yield increases of corn due to phosphorus fertilization within the rolling Pampa (Senigagliesi et al., 1984). Since then, soil phosphorus levels in the Pampas have decreased due to low rates of fertilization and intensifying crop over cattle production. Farmers have shown an increasing concern about soil fertility and crops response to fertilization. The use of P fertilizers in corn has increased in the last years (García, 2001).
More recently, several researchers have observed yield increases due to sulfur fertilization in the same region (southern Santa Fe and northern Buenos Aires) (Cordone et al., 2001; Gonzalez Montaner and Di Napoli, 2000; 2002; Pedrol et al., 2001; Thomas et al., 2001).
Phosphorus and Sulfur deficiencies may not occur as isolated events. They may appear at the same site, as both are related to long cropping history with low use of fertilizers. Little work have been done on P and S interaction effects on corn growth and yield.
Corn yield is mainly determined by the number of grains per unit area. The number of grains is strongly associated with the crop growth rate during a critical period of 40 days centered on silking (Andrade, 1995). Dry matter accumulation during this period depends on intercepted radiation and radiation use efficiency. Plenet et al. (2000) in France observed that P fertilization increased intercepted radiation without affecting radiation use efficiency. We could not find any study about the effects of sulfur nutrition on radiation interception and use.

Objectives
Six field experiments will be carry out to: a- determine crop response to P and S fertilization, b- quantify fertilization effects on yield-formation mechanisms, and c- detect K deficiencies.

Experimental Design
Six field experiments will be carried out in the center-north of the province of Buenos Aires, and in the south of the province of Santa Fe. Each experiment will have 5 treatments with 4 replications in a randomized complete block design. Plot size will be 15 m by 8 rows. Treatments will be: 1- Control, 2- P (30 kg P ha-1), 3- S (15 kg S ha-1), 4- P and S, 5- P, S, and K (150 kg K ha-1). The first 4 treatments constitute a factorial design with two levels of both, P and S.
We plan to measure crop development, radiation interception, air temperature, soil water content and to take plant and soil samples at several dates during the crop cycle. Plant material will be used to determine leaf area, biomass, crop growth rate around silking, grain yield, yield components (grain number and size). Data collected will be statistically analyzed by ANOVA. The experimental design allows us to test interactions between P and S, and P and K.