Effects of N, P and K on yields of cotton were investigated using data obtained over an 18-year period from a factorial experiment comparing various combinations of the three nutrients. The results clearly indicated a significant and fairly consistent response of cotton to the application of fertilizer nitrogen, but the rate of increase in yield with increased N gradually diminished. The response to P was erratic and to K was negligible. The response to N did not vary with levels of P or K. Whether lack of response to P on the alkaline soils of the Gezira was due to sufficient already available in the soil, or because the added fertilizer was fixed and rendered unavailable to the plant needs further investigation. Lack of response to added K was attributed to the high content of available K already in the Gezira soil.The effect of artificial fertilizers on the yield of cotton has been one of the main themes studied at the Gezira Research Station. The basic responses of cotton to the application of fertilizers were fairly well established from numerous shortterm investigations, in which nitrogenous fertilizers received the greatest attention, which was a natural consequence of the fact that the Gezira soils are inherently low in nitrogen and have shown very high responses to nitrogenous fertilizers. Comparatively less effort has been directed towards the study of other nutrients, to which only a limited response by cotton could be detected, and although numerous reports, over the years, have dealt with the effect of the amount, type, time and method of application of nitrogenous fertilizers, the literature pertinent to other nutrients is still very scanty.Various experiments have also been designed to study the long-term effect of different agronomic factors on the cotton crop, but the NPK experiment has been the only long-term investigation principally devoted to artificial fertilization of cotton. This was initiated in 1941 by F. Crowther, since when it has continued to be operated by various investigators, to measure the direct and cumulative effect of the three major nutrients-nitrogen, phosphorus and potassium-on the yield of cotton and their residual effect on lubia (a legume, Dolichos lablab) which was included in the rotation with cotton. The experiment was also intended to test whether the need for these nutrients changed with time. This paper deals primarily with the effect of the three nutrients on the yield of cotton.Short notes on the annual results of the NPK experiments have appeared in several reports of the Gezira Research Station. Dutta Roy (1955) prepared a note on the experiment in which the method of statistical analysis of data for several seasons was demonstrated, and this note has been a useful guide in the analysis and presentation of data reported in this paper. In the 1951-2 report Fowler, reviewing the results of several years of the experiment, considered that

SUMMARYTrials were made of the performance of batches of forage sorghum and maize, sown at different times of year. The optimum sowing periods of sorghum variety Abu Sabeen and maize variety 113 were found to be February to October and November to January respectively. Of the various climatic factors considered in this study, mean daily temperature was of greatest importance in affecting yield. The overall performance of sorghum was superior to that of maize, probably because of its relatively higher salt tolerance.

The rotation responses of unfertilized cotton were investigated using data obtained over a 28-year period from an experiment comparing ten rotations in various combinations of cotton with fallow and an alternating crop of dura (a sorghum millet) and lubia (a legume).

Summary: Résumé: Zusammenfassung Unrestricted weed growth resulted in serious yield losses (67–78%) in cotton (Gossypium barbadense L.). Hand‐weeding once at 6 weeks after crop sowing was ineffective (48% loss). In plots treated with oxidiazon, cotton yield progressively decreased as applications were made earlier than planting time. Spraying with 1.07 kg ha−1 30 days prior to sowing gave 54–69% less yield than the same dose applied at or within 7 days of sowing. Oxadiazon at sowing gave better weed control than pre‐sowing treatments and required less time for supplementary weeding. Air‐dry weight of weeds as a percentage of the unweeded plots was 74% when the herbicide treatments were made 30 days before sowing, but was only 10% when the herbicide treatments were made at sowing. Chemical analysis of soil samples collected from the treated plots at sowing revealed that 6.5, 74 and 78% of the applied dose was recoverable from plots treated 30, 15 and 7 days before planting. Influence de l'époque d'application de l'oxadiazon sur l'efficacité de l'herbicide en culture de cotonnier au Gezira du Soudan La libre croissance des mauvaises herbes a amené des pertes importantes (67–78%) dans le rendement du coton (Gossypium barbadense L.). Le désherbage manuel 6 semaines après le semis s'est montré inefficace (perte de 48%). Sur des parcelles recevant l'oxadiazon, les rendementsen coton ont diminuéà mesure que les applications préeédaient le semis. Une pulvérisation de 1,07 kg ha−1 30 jours avant le semis a donné un rendement inférieur de 54 a 69%à celui obtenu avec la même dose appliquée pas plus que 7 jours avant le semis. Appliqué au moment du semis, l'oxadiazon a permis une maîtrise des adventices supérieure à celle des traitements de pré‐semis; il a également exigé un désherbage supplémentaire moins onéreux. Lors des traitements 30 jours avant le semis, le poids sec des mauvaises herbes etait 74% de celui des adventices sur les parcelles non‐traitées mais les traitements au moment du semis ont réduit ce chiffre a 10%. Une analyse chimique d'échantillons de terre, prélevées au moment du semis sur les parcelles traitées, a révélé que 6,5%, 74% et 78% de la dose appliquée était récupérable sur les parcelles traitées 30, 15 et 7 jours avant le semis respectivement. Ueber den Einfluss des Zeitpunktes der Behandlung auf die herbizide Wirkung von Oxadiazon in Baumwolle im Sudan (Gezira) Ungehinderte Unkrautentwicklung in Baumwolle (Gossypium barbadense L.) verursacht grosse Ernteverluste (67–78%). Manuelle Unkrautbeseitigung 6 Wochen nach der Aussaat war praktisch wirkungslos (Verlust 48%). Je früher vor der Baumwollsaat die Parzellen mit Oxadiazon behandelt worden waren, deasto mehr nahm der Ernteertrag ab. Eine Behandlung mit 1,07 kg ha−1 30 Tage vor der Saat resulticrte in einem 54–69% geringeren Ertrag, als eine Behandlung mit derselben Dosierung bei der oder innert 7 Tagen nach der Saat. Oxadiazon zur Pflanzzeit appliziert, ergab eine bessere Unkrautbekämpfung als Behandlungen vor der Aussaat und erforderten weniger z...

Summary Studies on the germination of Ischaemum afrum seeds showed that low temperature, presence of glumes and both low and excessive soil moisture contents were conducive to delayed and low germination. The inhibitory effect of the glumes was more pronounced in freshly harvested seeds. Germinability of seeds on the soil surface was poor, but shallow burial in soil increased germination.