Nitrogen Immobilization by Congo Grass Roots Impairs Cotton Initial Growth

Abstract

In crop-livestock integration systems the presence of both grass roots in the soil and straw on the surface can temporarily immobilize nitrogen. This study examined the persistence of grass residues in the system as well as their effects on cotton response to N when grown after Congo grass (Brachiaria ruziziensis, Syn. Urochloa ruziziensis). Congo grass was grown in pots with soil. Next, cotton was grown in the same pots without residues, with whole plant residues (Congo grass roots and shoots) or root residues (grass roots) and fertilized with N as ammonium nitrate. Congo grass and cotton roots were separated using stable carbon isotope fractioning. Congo grass roots showed higher C/N ratio than shoots, losing 14% of its mass after 45 days and increasing soil N immobilization. The lower N availability resulted in N deficient and shorter cotton plants with lower dry matter yields. Nevertheless, the application of 80 to 120 mg kg -1 of N compensated the immobilization by the soil microorganisms, allowing cotton to show normal growth. When Congo grass is present in the cropping system, the effects of the decaying roots on soil N dynamics and availability are more important than those of the straw left on the soil surface.

Enhanced Plant Rooting and Crop System Management for Improved N Use Efficiency

“…Under no-till, the straw on the soil surface does not compete directly with the next crop for N, but root residues may impose some harm by immobilizing N. Cotton growth and N uptake were decreased when cropped in the presence of ruzigrass roots (Echer et al, 2012), and Rosolem et al (2012), by separating cotton roots from ruzigrass roots using C isotope fractioning, found that ruzigrass roots had high C/N ratios and had lost only 14% of its initial mass 45 days after termination, increasing soil N immobilization. The N returning from the straw on the soil surface was not enough to meet plant demand, which resulted in deficient cotton plants that required from 80 to 120 mg kg À1 of N to compensate for the immobilization.…”

Cover plants in second crop: nutrients in straw and cotton yield in succession

“…Trop., Goiânia, v. 53, e75032, 2023 Despite the higher dry matter yield in 2015 (Table 2) in the intercropping of C. spectabilis with U. ruziziensis, the yield and height of the cotton plants in succession were in the intermediate group, probably because of the lower amount of N (85 kg ha -1 ) in the higher dry matter contribution. Therefore, the soil N may have been immobilized, causing deficiency in the cotton plants, as reported by Rosolem et al (2012a).…”

Manejo Da Adubação Nitrogenada Antecipada Na Cultura Do Milho Cultivado Para Silagem Em Sucessão À Gramíneas Forrageiras E Cultura Do Feijão

“…Echer et al (2012) avaliando crescimento inicial do algodoeiro e absorção de nutrientes cultivada sobre resíduos de planta inteira, parte aérea e raiz de U. ruziziensis, observaram menor crescimento e teor de N na folha da cultura, quando esta foi cultivada sobre o sistema radicular da U. ruziziensis, atribuindo estas respostas a imobilização do N promovida pelos sistema radicular da U. ruziziensis. Em complemento a este trabalho de Echer et al (2012), Rosolem et al (2012) avaliaram cultivo de algodoeiro em vaso, sem resíduo (somente o solo), resíduos vegetais de U. ruziziensis planta inteira (parte aérea e raiz) e resíduos de raiz U. ruziziensis, em interação com adubação nitrogenada, e concluíram que a presença de raízes de U. ruziziensis, que possui baixa taxa de decomposição, alto conteúdo de suberina/lignina e elevada relação C/N, promoveram a imobilização temporária do N no solo e, consequentemente, repercutiram em menor absorção de N e produção de matéria seca pela planta de algodão. Entretanto, os autores salientam a importância da adubação nitrogenada via fertilizante para amenizar a imobilização do N no estádio inicial de desenvolvimento da cultura, quando esta é cultivada em sucessão a gramíneas forrageiras.…”